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Routing Information Protocol
Routing Information Protocol. The Routing Information Protocol (RIP) is one of the oldest distance-vector routing protocols which employ the hop count as a routing metric. RIP prevents routing loops by implementing limit on the number of hops allowed in a path from source to destination.
What is RIP Protocol?
The Routing Information Protocol (RIP) is one of the oldest distance-vector routing protocols which employ the hop count as a routing metric. RIP prevents routing loops by implementing limit on the number of hops allowed in a path from source to destination. The maximum number of hops allowed for RIP is 15, which limits the size of networks that RIP can support. A hop count of 16 is considered an infinite distance and the route is considered unreachable. RIP implements the split horizon, route poisoning and holddown mechanisms to prevent incorrect routing information from being propagated.
Originally, each RIP router transmitted full updates every 30 seconds. In the early deployments, routing tables were small enough that the traffic was not significant. As networks grew in size, however, it became evident there could be a massive traffic burst every 30 seconds, even if the routers had been initialized at random times. It was thought, as a result of random initialization, the routing updates would spread out in time, but this was not true in practice. Sally Floyd and Van Jacobson showed in 1994 that, without slight randomization of the update timer, the timers synchronized over time.
In most networking environments, RIP is not the preferred choice for routing as its time to converge and scalability are poor compared to EIGRP, OSPF, or IS-IS. However, it is easy to configure, because RIP does not require any parameters unlike other protocols.
What is meant by routing in computer networks?
Which protocol is the Internet based on?
Limitations Of Routing Information
The hop count cannot exceed 15, or routes will be dropped.
Most RIP networks are flat. There is no concept of areas or boundaries in RIP networks (but aggregation is possible).
Variable Length Subnet Masks are not supported by RIP version 1 (which is obsolete).
RIP has slow convergence and count to infinity problems.
Timers in Routing Information
The routing information protocol uses the following timers as part of its operation:
Update Timer
Invalid Timer
Flush Timer
Holddown Timer
Update Timer
The update timer controls the interval between two gratuitous Response Messages. By default the value is 30 seconds. The response message is broadcast to all its RIP enabled interface.
Invalid Timer
The invalid timer specifies how long a routing entry can be in the routing table without being updated. This is also called as expiration Timer. By default, the value is 180 seconds. After the timer expires the hop count of the routing entry will be set to 16, marking the destination as unreachable.
Flush Timer
The flush timer controls the time between the route is invalidated or marked as unreachable and removal of entry from the routing table. By default the value is 240 seconds. This is 60 seconds longer than Invalid timer. So for 60 seconds the router will be advertising about this unreachable route to all its neighbours. This timer must be set to a higher value than the invalid timer.
Hold-down Timer
The hold-down timer is started per route entry, when the hop count is changing from lower value to higher value. This allows the route to get stabilized. During this time no update can be done to that routing entry. This is not part of the RFC 1058. This is Cisco's implementation. The default value of this timer is 180 seconds.
Versions
There are three versions of the Routing Information Protocol: RIPv1, RIPv2, and RIPng.
RIP version 1
The original specification of RIP, defined in RFC 1058, was published in 1988 and uses classful routing. The periodic routing updates do not carry subnet information, lacking support for variable length subnet masks (VLSM). This limitation makes it impossible to have different-sized subnets inside of the same network class. In other words, all subnets in a network class must have the same size. There is also no support for router authentication, making RIP vulnerable to various attacks.
RIP version 2
Due to the deficiencies of the original RIP specification, RIP version 2 (RIPv2) was developed in 1993 and last standardized in 1998.[4] It included the ability to carry subnet information, thus supporting Classless Inter-Domain Routing (CIDR). To maintain backward compatibility, the hop count limit of 15 remained. RIPv2 has facilities to fully interoperate with the earlier specification if all Must Be Zero protocol fields in the RIPv1 messages are properly specified. In addition, a compatibility switch feature allows fine-grained interoperability adjustments.
In an effort to avoid unnecessary load on hosts that do not participate in routing, RIPv2 multicasts the entire routing table to all adjacent routers at the address 224.0.0.9, as opposed to RIPv1 which uses broadcast. Unicast addressing is still allowed for special applications.
(MD5) authentication for RIP was introduced in 1997.
RIPv2 is Internet Standard STD56 (which is RFC 2453).
Route tags were also added in RIP version 2. This functionality allows a distinction between routes learned from the RIP protocol and routes learned from other protocols.
RIPng
RIPng (RIP next generation), defined in RFC 2080, is an extension of RIPv2 for support of IPv6, the next generation Internet Protocol. The main differences between RIPv2 and RIPng are:
Support of IPv6 networking.
While RIPv2 supports RIPv1 updates authentication, RIPng does not. IPv6 routers were, at the time, supposed to use IPsec for authentication.
RIPv2 encodes the next-hop into each route entry, RIPng requires specific encoding of the next hop for a set of route entries.
RIPng sends updates on UDP port 521 using the multicast group FF02::9.
RIPv1 Operation
RIP defines two types of messages.
Request Message
When a RIP router comes online, it sends a broadcast Request Message on all of its RIP enabled interfaces. All the neighbouring routers which receive the Request message respond back with the Response Message containing their Routing table. The Response Message is also gratuitously sent when the Update timer expires. On receiving the Routing table, the router processes each entry of the routing table as per the following rules
If there are no route entries matching the one received then the route entry is added to the routing table automatically, along with the information about the router from which it received the routing table.
If there are matching entries but the hop count metric is lower than the one already in its routing table, then the routing table is updated with the new route.
If there are matching entries but the hop count metric is higher than the one already in its routing table, then the routing entry is updated with hop count of 16 (infinite hop). The packets are still forwarded to the old route. A Holddown timer is started and all the updates for that from other routers are ignored. If after the Holddown timer expires and still the router is advertising with the same higher hop count then the value is updated into its routing table. Only after the timer expires, the updates from other routers are accepted for that route.
What is an Internet protocol?
The Internet Protocol (IP) is the principal communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet.
IP has the task of delivering packets from the source host to the destination host solely based on the IP addresses in the packet headers. For this purpose, IP defines packet structures that encapsulate the data to be delivered. It also defines addressing methods that are used to label the datagram with source and destination information.
Historically, IP was the connectionless datagram service in the original Transmission Control Program introduced by Vint Cerf and Bob Kahn in 1974; the other being the connection-oriented Transmission Control Protocol (TCP). The Internet protocol suite is therefore often referred to as TCP/IP.
The first major version of IP, Internet Protocol Version 4 (IPv4), is the dominant protocol of the Internet. Its successor is Internet Protocol Version 6 (IPv6).
Functions
The Internet Protocol is responsible for addressing hosts and for routing datagrams (packets) from a source host to a destination host across one or more IP networks. For this purpose, the Internet Protocol defines the format of packets and provides an addressing system that has two functions: Identifying hosts and providing a logical location service.
Datagram construction
Sample encapsulation of application data from UDP to a Link protocol frame
Each datagram has two components: a header and a payload. The IP header is tagged with the source IP address, the destination IP address, and other meta-data needed to route and deliver the datagram. The payload is the data that is transported. This method of nesting the data payload in a packet with a header is called encapsulation.
IP addressing and routing
IP addressing entails the assignment of IP addresses and associated parameters to host interfaces. The address space is divided into networks and subnetworks, involving the designation of network or routing prefixes. IP routing is performed by all hosts, as well as routers, whose main function is to transport packets across network boundaries. Routers communicate with one another via specially designed routing protocols, either interior gateway protocols or exterior gateway protocols, as needed for the topology of the network.
IP routing is also common in local networks. For example, many Ethernet switches support IP multicast operations. These switches use IP addresses and Internet Group Management Protocol to control multicast routing but use MAC addresses for the actual routing.
Security
During the design phase of the ARPANET and the early Internet, the security aspects and needs of a public, international network could not be adequately anticipated. Consequently, many Internet protocols exhibited vulnerabilities highlighted by network attacks and later security assessments. In 2008, a thorough security assessment and proposed mitigation of problems was published. The Internet Engineering Task Force (IETF) has been pursuing further studies.
What is meant by routing in computer networks?
IP Routing
IP Routing is an umbrella term for the set of protocols that determine the path that data follows in order to travel across multiple networks from its source to its destination. Data is routed from its source to its destination through a series of routers, and across multiple networks. The IP Routing protocols enable routers to build up a forwarding table that correlates final destinations with next hop addresses.
These protocols include:
BGP (Border Gateway Protocol)
IS-IS (Intermediate System - Intermediate System)
OSPF (Open Shortest Path First)
RIP (Routing Information Protocol)
When an IP packet is to be forwarded, a router uses its forwarding table to determine the next hop for the packet's destination (based on the destination IP address in the IP packet header), and forwards the packet appropriately. The next router then repeats this process using its own forwarding table, and so on until the packet reaches its destination. At each stage, the IP address in the packet header is sufficient information to determine the next hop; no additional protocol headers are required.
The Internet, for the purpose of routing, is divided into Autonomous Systems (ASs). An AS is a group of routers that are under the control of a single administration and exchange routing information using a common routing protocol. For example, a corporate intranet or an ISP network can usually be regarded as an individual AS. The Internet can be visualized as a partial mesh of ASs. An AS can be classified as one of the following three types.
A Stub AS has a single connection to one other AS. Any data sent to, or received from, a destination outside the AS must travel over that connection. A small campus network is an example of a stub AS.
A Transit AS has multiple connections to one or more ASs, which permits data that is not destined for a node within that AS to travel through it. An ISP network is an example of a transit AS.
A Multihomed AS also has multiple connections to one or more ASs, but it does not permit data received over one of these connections to be forwarded out of the AS again. In other words, it does not provide a transit service to other ASs. A Multihomed AS is similar to a Stub AS, except that the ingress and egress points for data traveling to or from the AS can be chosen from one of a number of connections, depending on which connection offers the shortest route to the eventual destination. A large enterprise network would normally be a multihomed AS.
An Interior Gateway Protocol (IGP) calculates routes within a single AS. The IGP enables nodes on different networks within an AS to send data to one another. The IGP also enables data to be forwarded across an AS from ingress to egress, when the AS is providing transit services.
Routes are distributed between ASs by an Exterior Gateway Protocol (EGP). The EGP enables routers within an AS to choose the best point of egress from the AS for the data they are trying to route.
The EGP and the IGPs running within each AS cooperate to route data across the Internet. The EGP determines the ASs that data must cross in order to reach its destination, and the IGP determines the path within each AS that data must follow to get from the point of ingress (or the point of origin) to the point of egress (or the final destination).
Which protocol is the Internet based on?
TCP/IP
In the two decades since their invention, the heterogeneity of networks has expanded further with the deployment of Ethernet, Token Ring, Fiber Distributed Data Interface (FDDI), X.25, Frame Relay, Switched Multimegabit Data Service (SMDS), Integrated Services Digital Network (ISDN), and most recently, Asynchronous Transfer Mode (ATM). The Internet protocols are the best proven approach to internetworking this diverse range of LAN and WAN technologies.
The Internet Protocol suite includes not only lower-level specifications, such as Transmission Control Protocol (TCP) and Internet Protocol (IP), but specifications for such common applications as electronic mail, terminal emulation, and file transfer. Figure 1 shows the TCP/IP protocol suite in relation to the OSI Reference model. Figure 2 shows some of the important Internet protocols and their relationship to the OSI Reference Model. For information on the OSI Reference model and the role of each layer, please refer to the document Internetworking Basics.
The Internet protocols are the most widely implemented multivendor protocol suite in use today. Support for at least part of the Internet Protocol suite is available from virtually every computer vendor.
TCP/IP Technology
This section describes technical aspects of TCP, IP, related protocols, and the environments in which these protocols operate. Because the primary focus of this document is routing (a layer 3 function), the discussion of TCP (a layer 4 protocol) will be relatively brief.
TCP
TCP is a connection-oriented transport protocol that sends data as an unstructured stream of bytes. By using sequence numbers and acknowledgment messages, TCP can provide a sending node with delivery information about packets transmitted to a destination node. Where data has been lost in transit from source to destination, TCP can retransmit the data until either a timeout condition is reached or until successful delivery has been achieved. TCP can also recognize duplicate messages and will discard them appropriately. If the sending computer is transmitting too fast for the receiving computer, TCP can employ flow control mechanisms to slow data transfer. TCP can also communicates delivery information to the upper-layer protocols and applications it supports. All these characteristics makes TCP an end-to-end reliable transport protocol. TCP is specified in RFC 793 leavingcisco.com.
Figure 1 – TCP/IP Protocol Suite in Relation to the OSI Reference Model
Figure 2 – Important Internet Protocols in Relation to the OSI Reference Model
Refer to the TCP section of Internet Protocols for more information.
IP
IP is the primary Layer 3 protocol in the Internet suite. In addition to internetwork routing, IP provides error reporting and fragmentation and reassembly of information units called datagrams for transmission over networks with different maximum data unit sizes. IP represents the heart of the Internet Protocol suite.
Note: The term IP in the section refers to IPv4 unless otherwise stated explicitly.
IP addresses are globally unique, 32-bit numbers assigned by the Network Information Center. Globally unique addresses permit IP networks anywhere in the world to communicate with each other.
An IP address is divided into two parts. The first part designates the network address while the second part designates the host address.
The IP address space is divided into different network classes. Class A networks are intended mainly for use with a few very large networks, because they provide only 8 bits for the network address field. Class B networks allocate 16 bits, and Class C networks allocate 24 bits for the network address field. Class C networks only provide 8 bits for the host field, however, so the number of hosts per network may be a limiting factor. In all three cases, the left most bit(s) indicate the network class. IP addresses are written in dotted decimal format; for example, 34.0.0.1. Figure 3 shows the address formats for Class A, B, and C IP networks.
Figure 3 – Address Formats for Class A, B, and C IP Networks
IP networks also can be divided into smaller units called subnetworks or "subnets." Subnets provide extra flexibility for the network administrator. For example, assume that a network has been assigned a Class A address and all the nodes on the network use a Class A address. Further assume that the dotted decimal representation of this network's address is 34.0.0.0. (All zeros in the host field of an address specify the entire network.) The administrator can subdivide the network using subnetting. This is done by "borrowing" bits from the host portion of the address and using them as a subnet field, as depicted in Figure 4.
Figure 4 – "Borrowing" Bits
If the network administrator has chosen to use 8 bits of subnetting, the second octet of a Class A IP address provides the subnet number. In our example, address 34.1.0.0 refers to network 34, subnet 1; address 34.2.0.0 refers to network 34, subnet 2, and so on.
The number of bits that can be borrowed for the subnet address varies. To specify how many bits are used to represent the network and the subnet portion of the address, IP provides subnet masks. Subnet masks use the same format and representation technique as IP addresses. Subnet masks have ones in all bits except those that specify the host field. For example, the subnet mask that specifies 8 bits of subnetting for Class A address 34.0.0.0 is 255.255.0.0. The subnet mask that specifies 16 bits of subnetting for Class A address 34.0.0.0 is 255.255.255.0. Both of these subnet masks are pictured in Figure 5. Subnet masks can be passed through a network on demand so that new nodes can learn how many bits of subnetting are being used on their network.
Figure 5 – Subnet Masks
Traditionally, all subnets of the same network number used the same subnet mask. In other words, a network manager would choose an eight-bit mask for all subnets in the network. This strategy is easy to manage for both network administrators and routing protocols. However, this practice wastes address space in some networks. Some subnets have many hosts and some have only a few, but each consumes an entire subnet number. Serial lines are the most extreme example, because each has only two hosts that can be connected via a serial line subnet.
As IP subnets have grown, administrators have looked for ways to use their address space more efficiently. One of the techniques that has resulted is called Variable Length Subnet Masks (VLSM). With VLSM, a network administrator can use a long mask on networks with few hosts and a short mask on subnets with many hosts. However, this technique is more complex than making them all one size, and addresses must be assigned carefully.
Of course in order to use VLSM, a network administrator must use a routing protocol that supports it. Cisco routers support VLSM with Open Shortest Path First (OSPF), Integrated Intermediate System to Intermediate System (Integrated IS-IS), Enhanced Interior Gateway Routing Protocol (Enhanced IGRP), and static routing. Refer to IP Addressing and Subnetting for New Users for more information about IP addressing and subnetting.
On some media, such as IEEE 802 LANs, IP addresses are dynamically discovered through the use of two other members of the Internet protocol suite: Address Resolution Protocol (ARP) and Reverse Address Resolution Protocol (RARP). ARP uses broadcast messages to determine the hardware (MAC layer) address corresponding to a particular network-layer address. ARP is sufficiently generic to allow use of IP with virtually any type of underlying media access mechanism. RARP uses broadcast messages to determine the network-layer address associated with a particular hardware address. RARP is especially important to diskless nodes, for which network-layer addresses usually are unknown at boot time.
Routing in IP Environments
An "internet" is a group of interconnected networks. The Internet, on the other hand, is the collection of networks that permits communication between most research institutions, universities, and many other organizations around the world. Routers within the Internet are organized hierarchically. Some routers are used to move information through one particular group of networks under the same administrative authority and control. (Such an entity is called an autonomous system.) Routers used for information exchange within autonomous systems are called interior routers, and they use a variety of interior gateway protocols (IGPs) to accomplish this end. Routers that move information between autonomous systems are called exterior routers; they use the Exterior Gateway Protocol (EGP) or Border Gateway Protocol (BGP). Figure 6 shows the Internet architecture.
Figure 6 – Representation of the Internet Architecture
Routing protocols used with IP are dynamic in nature. Dynamic routing requires the software in the routing devices to calculate routes. Dynamic routing algorithms adapt to changes in the network and automatically select the best routes. In contrast with dynamic routing, static routing calls for routes to be established by the network administrator. Static routes do not change until the network administrator changes them.
IP routing tables consist of destination address/next hop pairs. This sample routing table from a Cisco router shows that the first entry is interpreted as meaning "to get to network 34.1.0.0 (subnet 1 on network 34), the next stop is the node at address 54.34.23.12":
R6-2500# show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
34.0.0.0/16 is subnetted, 1 subnets
O 34.1.0.0 [110/65] via 54.34.23.12, 00:00:51, Serial0
54.0.0.0/24 is subnetted, 1 subnets
C 54.34.23.0 is directly connected, Serial0
R6-2500#
As we have seen, IP routing specifies that IP datagrams travel through an internetwork one router hop at a time. The entire route is not known at the outset of the journey. Instead, at each stop, the next router hop is determined by matching the destination address within the datagram with an entry in the current node's routing table. Each node's involvement in the routing process consists only of forwarding packets based on internal information. IP does not provide for error reporting back to the source when routing anomalies occur. This task is left to another Internet protocol—the Internet Control Message Protocol (ICMP).
ICMP performs a number of tasks within an IP internetwork. In addition to the principal reason for which it was created (reporting routing failures back to the source), ICMP provides a method for testing node reachability across an internet (the ICMP Echo and Reply messages), a method for increasing routing efficiency (the ICMP Redirect message), a method for informing sources that a datagram has exceeded its allocated time to exist within an internet (the ICMP Time Exceeded message), and other helpful messages. All in all, ICMP is an integral part of any IP implementation, particularly those that run in routers.
What is Routing table
In computer networking a routing table, or routing information base (RIB), is a data table stored in a router or a networked computer that lists the routes to particular network destinations, and in some cases, metrics (distances) associated with those routes. The routing table contains information about the topology of the network immediately around it. The construction of routing tables is the primary goal of routing protocols. Static routes are entries made in a routing table by non-automatic means and which are fixed rather than being the result of some network topology "discovery" procedure.
Basics
A routing table uses the same idea that one does when using a map in package delivery. Whenever a node needs to send data to another node on a network, it must first know where to send it. If the node cannot directly connect to the destination node, it has to send it via other nodes along a proper route to the destination node. Most nodes do not try to figure out which route(s) might work; instead, a node will send an IP packet to a gateway in the LAN, which then decides how to route the "package" of data to the correct destination. Each gateway will need to keep track of which way to deliver various packages of data, and for this it uses a Routing Table. A routing table is a database which keeps track of paths, like a map, and allows the gateway to provide this information to the node requesting the information.
With hop-by-hop routing, each routing table lists, for all reachable destinations, the address of the next device along the path to that destination: the next hop. Assuming that the routing tables are consistent, the simple algorithm of relaying packets to their destination's next hop thus suffices to deliver data anywhere in a network. Hop-by-hop is the fundamental characteristic of the IP Internetwork Layer and the OSI Network Layer.
The primary function of a router is to forward a packet toward its destination network, which is the destination IP address of the packet. To do this, a router needs to search the routing information stored in its routing table.
A routing table is a data file in RAM that is used to store route information about directly connected and remote networks. The routing table contains network/next hop associations. These associations tell a router that a particular destination can be optimally reached by sending the packet to a specific router that represents the "next hop" on the way to the final destination. The next hop association can also be the outgoing or exit interface to the final destination.
The network/exit-interface association can also represent the destination network address of the IP packet. This association occurs on the router's directly connected networks.
A directly connected network is a network that is directly attached to one of the router interfaces. When a router interface is configured with an IP address and subnet mask, the interface becomes a host on that attached network. The network address and subnet mask of the interface, along with the interface type and number, are entered into the routing table as a directly connected network. When a router forwards a packet to a host, such as a web server, that host is on the same network as a router's directly connected network.
A remote network is a network that is not directly connected to the router. In other words, a remote network is a network that can only be reached by sending the packet to another router. Remote networks are added to the routing table using either a dynamic routing protocol or by configuring static routes. Dynamic routes are routes to remote networks that were learned automatically by the router, using a dynamic routing protocol. Static routes are routes to networks that a network administrator manually configured.
Difficulties with routing tables
The need to record routes to large numbers of devices using limited storage space represents a major challenge in routing table construction. In the Internet, the currently dominant address aggregation technology is a bitwise prefix matching scheme called Classless Inter-Domain Routing (CIDR).
Contents of routing tables
The routing table consists of at least three information fields:
the network id: i.e. the destination subnet
cost/metric: i.e. the cost or metric of the path through which the packet is to be sent
next hop: The next hop, or gateway, is the address of the next station to which the packet is to be sent on the way to its final destination
Depending on the application and implementation, it can also contain additional values that refine path selection:
quality of service associated with the route. For example, the U flag indicates that an IP route is up.
links to filtering criteria/access lists associated with the route
interface: such as eth0 for the first Ethernet card, eth1 for the second Ethernet card, etc.
Routing tables are also a key aspect of certain security operations, such as unicast reverse path forwarding (uRPF). In this technique, which has several variants, the router also looks up, in the routing table, the source address of the packet. If there exists no route back to the source address, the packet is assumed to be malformed or involved in a network attack, and is dropped.
Shown below is an example of what the table above could look like on an average computer connected to the internet via a home router:
The column Network Destination and Netmask together describe the Network id as mentioned earlier. For example, destination 192.168.0.0 and netmask 255.255.255.0 can be written as network id 192.168.0.0/24.
The Gateway column contains the same information as the Next hop, i.e. it points to the gateway through which the network can be reached.
The Interface indicates what locally available interface is responsible for reaching the gateway. In this example, gateway 192.168.0.1 (the internet router) can be reached through the local network card with address 192.168.0.100.
Finally, the Metric indicates the associated cost of using the indicated route. This is useful for determining the efficiency of a certain route from two points in a network. In this example, it is more efficient to communicate with the computer itself through the use of address 127.0.0.1 (called “localhost”) than it would be through 192.168.0.100 (the IP address of the local network card).
Forwarding Table
Routing tables are generally not used directly for packet forwarding in modern router architectures; instead, they are used to generate the information for a smaller forwarding table. A forwarding table contains only the routes which are chosen by the routing algorithm as preferred routes for packet forwarding. It is often in a compressed or pre-compiled format that is optimized for hardware storage and lookup.
This router architecture separates the Control Plane function of the routing table from the Forwarding Plane function of the forwarding table. This separation of control and forwarding provides uninterrupted performance.
How to Login Cisco Router
A. All routers have a built-in web-based setup page that allows you to customize settings and set up advanced properties.
Note: Before you access the web-based setup page of the router, make sure the router is powered on and the computer is wired to one of the Ethernet ports on the router, for example, 1, 2, 3 or 4.
Complete these steps:
Open a web browser such as Internet Explorer.
Go to the Address bar and enter the IP Address of your router then press Enter. For example,
192.168.15.1 is the default IP of most VOIP routers.
If the IP address of the router has been changed, type the IP address of the router in the Address bar instead.
The IP address of the router can be changed by these factors:
If you run the setup CD of the router
If you change it on the web-based setup page of the router
If you forgot the IP address of the router, you can try one of these steps:
Check the IP address of the router.
Press the Reset button at the back of the router for 30 seconds.
This procedure resets your router to factory defaults. Any settings on the router are erased. The IP address of the router will be 192.168.15.1 and the password is admin after you reset it.
A new window prompts for a User name and Password. Type admin for User name and Password, since admin is the default user name password, and then click OK.
If the password of the router has been changed, type the new password of the router in the Password field instead.
The password of the router can be changed by these factors:
If you run the setup CD of the router.
If you change it on the web-based setup page of the router.
Cisco Career Certifications
We offer five levels of network certification: Entry, Associate, Professional, Expert and Architect, the highest level of accreditation within the Cisco Career Certification program.
Not sure which certification to pursue? Explore the Career Guide.
Entry Certifications
Both the CCENT and the CCT certifications serve as starting points for individuals interested in starting a career as a networking professional.
CCENT
CCT
Associate Certifications
The Associate level of Cisco Certifications can begin directly with CCNA for network installation, operations and troubleshooting or CCDA for network design. Think of the Associate Level as the foundation level of networking certification.
CCDA
CCNA Cloud
CCNA Collaboration
CCNA Cyber Ops
CCNA Data Center
CCNA Industrial
CCNA Routing and Switching
CCNA Security
CCNA Service Provider
CCNA Wireless
Professional Certifications
The Professional level is an advanced level of certification that shows more expertise with networking skills. Each certification covers a different technology to meet the needs of varying job roles.
CCDP
CCNP Cloud
CCNP Collaboration
CCNP Data Center
CCNP Routing and Switching
CCNP Security
CCNP Service Provider
CCNP Wireless
Expert Certifications
The Cisco Certified Internetwork Expert (CCIE) certification is accepted worldwide as the most prestigious networking certification in the industry.
CCDE
CCIE Collaboration
CCIE Data Center
CCIE Routing and Switching
CCIE Security
CCIE Service Provider
CCIE Wireless
Architect Certification
Cisco Certified Architect is the highest level of accreditation achievable and recognizes the architectural expertise of network designers who can support the increasingly complex networks of global organizations and effectively translate business strategies into evolutionary technical strategies.
CCAr
Routing Information Protocol. The Routing Information Protocol (RIP) is one of the oldest distance-vector routing protocols which employ the hop count as a routing metric. RIP prevents routing loops by implementing limit on the number of hops allowed in a path from source to destination.
What is RIP Protocol?
The Routing Information Protocol (RIP) is one of the oldest distance-vector routing protocols which employ the hop count as a routing metric. RIP prevents routing loops by implementing limit on the number of hops allowed in a path from source to destination. The maximum number of hops allowed for RIP is 15, which limits the size of networks that RIP can support. A hop count of 16 is considered an infinite distance and the route is considered unreachable. RIP implements the split horizon, route poisoning and holddown mechanisms to prevent incorrect routing information from being propagated.
Originally, each RIP router transmitted full updates every 30 seconds. In the early deployments, routing tables were small enough that the traffic was not significant. As networks grew in size, however, it became evident there could be a massive traffic burst every 30 seconds, even if the routers had been initialized at random times. It was thought, as a result of random initialization, the routing updates would spread out in time, but this was not true in practice. Sally Floyd and Van Jacobson showed in 1994 that, without slight randomization of the update timer, the timers synchronized over time.
In most networking environments, RIP is not the preferred choice for routing as its time to converge and scalability are poor compared to EIGRP, OSPF, or IS-IS. However, it is easy to configure, because RIP does not require any parameters unlike other protocols.
What is meant by routing in computer networks?
Which protocol is the Internet based on?
Limitations Of Routing Information
The hop count cannot exceed 15, or routes will be dropped.
Most RIP networks are flat. There is no concept of areas or boundaries in RIP networks (but aggregation is possible).
Variable Length Subnet Masks are not supported by RIP version 1 (which is obsolete).
RIP has slow convergence and count to infinity problems.
Timers in Routing Information
The routing information protocol uses the following timers as part of its operation:
Update Timer
Invalid Timer
Flush Timer
Holddown Timer
Update Timer
The update timer controls the interval between two gratuitous Response Messages. By default the value is 30 seconds. The response message is broadcast to all its RIP enabled interface.
Invalid Timer
The invalid timer specifies how long a routing entry can be in the routing table without being updated. This is also called as expiration Timer. By default, the value is 180 seconds. After the timer expires the hop count of the routing entry will be set to 16, marking the destination as unreachable.
Flush Timer
The flush timer controls the time between the route is invalidated or marked as unreachable and removal of entry from the routing table. By default the value is 240 seconds. This is 60 seconds longer than Invalid timer. So for 60 seconds the router will be advertising about this unreachable route to all its neighbours. This timer must be set to a higher value than the invalid timer.
Hold-down Timer
The hold-down timer is started per route entry, when the hop count is changing from lower value to higher value. This allows the route to get stabilized. During this time no update can be done to that routing entry. This is not part of the RFC 1058. This is Cisco's implementation. The default value of this timer is 180 seconds.
Versions
There are three versions of the Routing Information Protocol: RIPv1, RIPv2, and RIPng.
RIP version 1
The original specification of RIP, defined in RFC 1058, was published in 1988 and uses classful routing. The periodic routing updates do not carry subnet information, lacking support for variable length subnet masks (VLSM). This limitation makes it impossible to have different-sized subnets inside of the same network class. In other words, all subnets in a network class must have the same size. There is also no support for router authentication, making RIP vulnerable to various attacks.
RIP version 2
Due to the deficiencies of the original RIP specification, RIP version 2 (RIPv2) was developed in 1993 and last standardized in 1998.[4] It included the ability to carry subnet information, thus supporting Classless Inter-Domain Routing (CIDR). To maintain backward compatibility, the hop count limit of 15 remained. RIPv2 has facilities to fully interoperate with the earlier specification if all Must Be Zero protocol fields in the RIPv1 messages are properly specified. In addition, a compatibility switch feature allows fine-grained interoperability adjustments.
In an effort to avoid unnecessary load on hosts that do not participate in routing, RIPv2 multicasts the entire routing table to all adjacent routers at the address 224.0.0.9, as opposed to RIPv1 which uses broadcast. Unicast addressing is still allowed for special applications.
(MD5) authentication for RIP was introduced in 1997.
RIPv2 is Internet Standard STD56 (which is RFC 2453).
Route tags were also added in RIP version 2. This functionality allows a distinction between routes learned from the RIP protocol and routes learned from other protocols.
RIPng
RIPng (RIP next generation), defined in RFC 2080, is an extension of RIPv2 for support of IPv6, the next generation Internet Protocol. The main differences between RIPv2 and RIPng are:
Support of IPv6 networking.
While RIPv2 supports RIPv1 updates authentication, RIPng does not. IPv6 routers were, at the time, supposed to use IPsec for authentication.
RIPv2 encodes the next-hop into each route entry, RIPng requires specific encoding of the next hop for a set of route entries.
RIPng sends updates on UDP port 521 using the multicast group FF02::9.
RIPv1 Operation
RIP defines two types of messages.
Request Message
When a RIP router comes online, it sends a broadcast Request Message on all of its RIP enabled interfaces. All the neighbouring routers which receive the Request message respond back with the Response Message containing their Routing table. The Response Message is also gratuitously sent when the Update timer expires. On receiving the Routing table, the router processes each entry of the routing table as per the following rules
If there are no route entries matching the one received then the route entry is added to the routing table automatically, along with the information about the router from which it received the routing table.
If there are matching entries but the hop count metric is lower than the one already in its routing table, then the routing table is updated with the new route.
If there are matching entries but the hop count metric is higher than the one already in its routing table, then the routing entry is updated with hop count of 16 (infinite hop). The packets are still forwarded to the old route. A Holddown timer is started and all the updates for that from other routers are ignored. If after the Holddown timer expires and still the router is advertising with the same higher hop count then the value is updated into its routing table. Only after the timer expires, the updates from other routers are accepted for that route.
What is an Internet protocol?
The Internet Protocol (IP) is the principal communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet.
IP has the task of delivering packets from the source host to the destination host solely based on the IP addresses in the packet headers. For this purpose, IP defines packet structures that encapsulate the data to be delivered. It also defines addressing methods that are used to label the datagram with source and destination information.
Historically, IP was the connectionless datagram service in the original Transmission Control Program introduced by Vint Cerf and Bob Kahn in 1974; the other being the connection-oriented Transmission Control Protocol (TCP). The Internet protocol suite is therefore often referred to as TCP/IP.
The first major version of IP, Internet Protocol Version 4 (IPv4), is the dominant protocol of the Internet. Its successor is Internet Protocol Version 6 (IPv6).
Functions
The Internet Protocol is responsible for addressing hosts and for routing datagrams (packets) from a source host to a destination host across one or more IP networks. For this purpose, the Internet Protocol defines the format of packets and provides an addressing system that has two functions: Identifying hosts and providing a logical location service.
Datagram construction
Sample encapsulation of application data from UDP to a Link protocol frame
Each datagram has two components: a header and a payload. The IP header is tagged with the source IP address, the destination IP address, and other meta-data needed to route and deliver the datagram. The payload is the data that is transported. This method of nesting the data payload in a packet with a header is called encapsulation.
IP addressing and routing
IP addressing entails the assignment of IP addresses and associated parameters to host interfaces. The address space is divided into networks and subnetworks, involving the designation of network or routing prefixes. IP routing is performed by all hosts, as well as routers, whose main function is to transport packets across network boundaries. Routers communicate with one another via specially designed routing protocols, either interior gateway protocols or exterior gateway protocols, as needed for the topology of the network.
IP routing is also common in local networks. For example, many Ethernet switches support IP multicast operations. These switches use IP addresses and Internet Group Management Protocol to control multicast routing but use MAC addresses for the actual routing.
Security
During the design phase of the ARPANET and the early Internet, the security aspects and needs of a public, international network could not be adequately anticipated. Consequently, many Internet protocols exhibited vulnerabilities highlighted by network attacks and later security assessments. In 2008, a thorough security assessment and proposed mitigation of problems was published. The Internet Engineering Task Force (IETF) has been pursuing further studies.
What is meant by routing in computer networks?
IP Routing
IP Routing is an umbrella term for the set of protocols that determine the path that data follows in order to travel across multiple networks from its source to its destination. Data is routed from its source to its destination through a series of routers, and across multiple networks. The IP Routing protocols enable routers to build up a forwarding table that correlates final destinations with next hop addresses.
These protocols include:
BGP (Border Gateway Protocol)
IS-IS (Intermediate System - Intermediate System)
OSPF (Open Shortest Path First)
RIP (Routing Information Protocol)
When an IP packet is to be forwarded, a router uses its forwarding table to determine the next hop for the packet's destination (based on the destination IP address in the IP packet header), and forwards the packet appropriately. The next router then repeats this process using its own forwarding table, and so on until the packet reaches its destination. At each stage, the IP address in the packet header is sufficient information to determine the next hop; no additional protocol headers are required.
The Internet, for the purpose of routing, is divided into Autonomous Systems (ASs). An AS is a group of routers that are under the control of a single administration and exchange routing information using a common routing protocol. For example, a corporate intranet or an ISP network can usually be regarded as an individual AS. The Internet can be visualized as a partial mesh of ASs. An AS can be classified as one of the following three types.
A Stub AS has a single connection to one other AS. Any data sent to, or received from, a destination outside the AS must travel over that connection. A small campus network is an example of a stub AS.
A Transit AS has multiple connections to one or more ASs, which permits data that is not destined for a node within that AS to travel through it. An ISP network is an example of a transit AS.
A Multihomed AS also has multiple connections to one or more ASs, but it does not permit data received over one of these connections to be forwarded out of the AS again. In other words, it does not provide a transit service to other ASs. A Multihomed AS is similar to a Stub AS, except that the ingress and egress points for data traveling to or from the AS can be chosen from one of a number of connections, depending on which connection offers the shortest route to the eventual destination. A large enterprise network would normally be a multihomed AS.
An Interior Gateway Protocol (IGP) calculates routes within a single AS. The IGP enables nodes on different networks within an AS to send data to one another. The IGP also enables data to be forwarded across an AS from ingress to egress, when the AS is providing transit services.
Routes are distributed between ASs by an Exterior Gateway Protocol (EGP). The EGP enables routers within an AS to choose the best point of egress from the AS for the data they are trying to route.
The EGP and the IGPs running within each AS cooperate to route data across the Internet. The EGP determines the ASs that data must cross in order to reach its destination, and the IGP determines the path within each AS that data must follow to get from the point of ingress (or the point of origin) to the point of egress (or the final destination).
Which protocol is the Internet based on?
TCP/IP
In the two decades since their invention, the heterogeneity of networks has expanded further with the deployment of Ethernet, Token Ring, Fiber Distributed Data Interface (FDDI), X.25, Frame Relay, Switched Multimegabit Data Service (SMDS), Integrated Services Digital Network (ISDN), and most recently, Asynchronous Transfer Mode (ATM). The Internet protocols are the best proven approach to internetworking this diverse range of LAN and WAN technologies.
The Internet Protocol suite includes not only lower-level specifications, such as Transmission Control Protocol (TCP) and Internet Protocol (IP), but specifications for such common applications as electronic mail, terminal emulation, and file transfer. Figure 1 shows the TCP/IP protocol suite in relation to the OSI Reference model. Figure 2 shows some of the important Internet protocols and their relationship to the OSI Reference Model. For information on the OSI Reference model and the role of each layer, please refer to the document Internetworking Basics.
The Internet protocols are the most widely implemented multivendor protocol suite in use today. Support for at least part of the Internet Protocol suite is available from virtually every computer vendor.
TCP/IP Technology
This section describes technical aspects of TCP, IP, related protocols, and the environments in which these protocols operate. Because the primary focus of this document is routing (a layer 3 function), the discussion of TCP (a layer 4 protocol) will be relatively brief.
TCP
TCP is a connection-oriented transport protocol that sends data as an unstructured stream of bytes. By using sequence numbers and acknowledgment messages, TCP can provide a sending node with delivery information about packets transmitted to a destination node. Where data has been lost in transit from source to destination, TCP can retransmit the data until either a timeout condition is reached or until successful delivery has been achieved. TCP can also recognize duplicate messages and will discard them appropriately. If the sending computer is transmitting too fast for the receiving computer, TCP can employ flow control mechanisms to slow data transfer. TCP can also communicates delivery information to the upper-layer protocols and applications it supports. All these characteristics makes TCP an end-to-end reliable transport protocol. TCP is specified in RFC 793 leavingcisco.com.
Figure 1 – TCP/IP Protocol Suite in Relation to the OSI Reference Model
Figure 2 – Important Internet Protocols in Relation to the OSI Reference Model
Refer to the TCP section of Internet Protocols for more information.
IP
IP is the primary Layer 3 protocol in the Internet suite. In addition to internetwork routing, IP provides error reporting and fragmentation and reassembly of information units called datagrams for transmission over networks with different maximum data unit sizes. IP represents the heart of the Internet Protocol suite.
Note: The term IP in the section refers to IPv4 unless otherwise stated explicitly.
IP addresses are globally unique, 32-bit numbers assigned by the Network Information Center. Globally unique addresses permit IP networks anywhere in the world to communicate with each other.
An IP address is divided into two parts. The first part designates the network address while the second part designates the host address.
The IP address space is divided into different network classes. Class A networks are intended mainly for use with a few very large networks, because they provide only 8 bits for the network address field. Class B networks allocate 16 bits, and Class C networks allocate 24 bits for the network address field. Class C networks only provide 8 bits for the host field, however, so the number of hosts per network may be a limiting factor. In all three cases, the left most bit(s) indicate the network class. IP addresses are written in dotted decimal format; for example, 34.0.0.1. Figure 3 shows the address formats for Class A, B, and C IP networks.
Figure 3 – Address Formats for Class A, B, and C IP Networks
IP networks also can be divided into smaller units called subnetworks or "subnets." Subnets provide extra flexibility for the network administrator. For example, assume that a network has been assigned a Class A address and all the nodes on the network use a Class A address. Further assume that the dotted decimal representation of this network's address is 34.0.0.0. (All zeros in the host field of an address specify the entire network.) The administrator can subdivide the network using subnetting. This is done by "borrowing" bits from the host portion of the address and using them as a subnet field, as depicted in Figure 4.
Figure 4 – "Borrowing" Bits
If the network administrator has chosen to use 8 bits of subnetting, the second octet of a Class A IP address provides the subnet number. In our example, address 34.1.0.0 refers to network 34, subnet 1; address 34.2.0.0 refers to network 34, subnet 2, and so on.
The number of bits that can be borrowed for the subnet address varies. To specify how many bits are used to represent the network and the subnet portion of the address, IP provides subnet masks. Subnet masks use the same format and representation technique as IP addresses. Subnet masks have ones in all bits except those that specify the host field. For example, the subnet mask that specifies 8 bits of subnetting for Class A address 34.0.0.0 is 255.255.0.0. The subnet mask that specifies 16 bits of subnetting for Class A address 34.0.0.0 is 255.255.255.0. Both of these subnet masks are pictured in Figure 5. Subnet masks can be passed through a network on demand so that new nodes can learn how many bits of subnetting are being used on their network.
Figure 5 – Subnet Masks
Traditionally, all subnets of the same network number used the same subnet mask. In other words, a network manager would choose an eight-bit mask for all subnets in the network. This strategy is easy to manage for both network administrators and routing protocols. However, this practice wastes address space in some networks. Some subnets have many hosts and some have only a few, but each consumes an entire subnet number. Serial lines are the most extreme example, because each has only two hosts that can be connected via a serial line subnet.
As IP subnets have grown, administrators have looked for ways to use their address space more efficiently. One of the techniques that has resulted is called Variable Length Subnet Masks (VLSM). With VLSM, a network administrator can use a long mask on networks with few hosts and a short mask on subnets with many hosts. However, this technique is more complex than making them all one size, and addresses must be assigned carefully.
Of course in order to use VLSM, a network administrator must use a routing protocol that supports it. Cisco routers support VLSM with Open Shortest Path First (OSPF), Integrated Intermediate System to Intermediate System (Integrated IS-IS), Enhanced Interior Gateway Routing Protocol (Enhanced IGRP), and static routing. Refer to IP Addressing and Subnetting for New Users for more information about IP addressing and subnetting.
On some media, such as IEEE 802 LANs, IP addresses are dynamically discovered through the use of two other members of the Internet protocol suite: Address Resolution Protocol (ARP) and Reverse Address Resolution Protocol (RARP). ARP uses broadcast messages to determine the hardware (MAC layer) address corresponding to a particular network-layer address. ARP is sufficiently generic to allow use of IP with virtually any type of underlying media access mechanism. RARP uses broadcast messages to determine the network-layer address associated with a particular hardware address. RARP is especially important to diskless nodes, for which network-layer addresses usually are unknown at boot time.
Routing in IP Environments
An "internet" is a group of interconnected networks. The Internet, on the other hand, is the collection of networks that permits communication between most research institutions, universities, and many other organizations around the world. Routers within the Internet are organized hierarchically. Some routers are used to move information through one particular group of networks under the same administrative authority and control. (Such an entity is called an autonomous system.) Routers used for information exchange within autonomous systems are called interior routers, and they use a variety of interior gateway protocols (IGPs) to accomplish this end. Routers that move information between autonomous systems are called exterior routers; they use the Exterior Gateway Protocol (EGP) or Border Gateway Protocol (BGP). Figure 6 shows the Internet architecture.
Figure 6 – Representation of the Internet Architecture
Routing protocols used with IP are dynamic in nature. Dynamic routing requires the software in the routing devices to calculate routes. Dynamic routing algorithms adapt to changes in the network and automatically select the best routes. In contrast with dynamic routing, static routing calls for routes to be established by the network administrator. Static routes do not change until the network administrator changes them.
IP routing tables consist of destination address/next hop pairs. This sample routing table from a Cisco router shows that the first entry is interpreted as meaning "to get to network 34.1.0.0 (subnet 1 on network 34), the next stop is the node at address 54.34.23.12":
R6-2500# show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
34.0.0.0/16 is subnetted, 1 subnets
O 34.1.0.0 [110/65] via 54.34.23.12, 00:00:51, Serial0
54.0.0.0/24 is subnetted, 1 subnets
C 54.34.23.0 is directly connected, Serial0
R6-2500#
As we have seen, IP routing specifies that IP datagrams travel through an internetwork one router hop at a time. The entire route is not known at the outset of the journey. Instead, at each stop, the next router hop is determined by matching the destination address within the datagram with an entry in the current node's routing table. Each node's involvement in the routing process consists only of forwarding packets based on internal information. IP does not provide for error reporting back to the source when routing anomalies occur. This task is left to another Internet protocol—the Internet Control Message Protocol (ICMP).
ICMP performs a number of tasks within an IP internetwork. In addition to the principal reason for which it was created (reporting routing failures back to the source), ICMP provides a method for testing node reachability across an internet (the ICMP Echo and Reply messages), a method for increasing routing efficiency (the ICMP Redirect message), a method for informing sources that a datagram has exceeded its allocated time to exist within an internet (the ICMP Time Exceeded message), and other helpful messages. All in all, ICMP is an integral part of any IP implementation, particularly those that run in routers.
What is Routing table
In computer networking a routing table, or routing information base (RIB), is a data table stored in a router or a networked computer that lists the routes to particular network destinations, and in some cases, metrics (distances) associated with those routes. The routing table contains information about the topology of the network immediately around it. The construction of routing tables is the primary goal of routing protocols. Static routes are entries made in a routing table by non-automatic means and which are fixed rather than being the result of some network topology "discovery" procedure.
Basics
A routing table uses the same idea that one does when using a map in package delivery. Whenever a node needs to send data to another node on a network, it must first know where to send it. If the node cannot directly connect to the destination node, it has to send it via other nodes along a proper route to the destination node. Most nodes do not try to figure out which route(s) might work; instead, a node will send an IP packet to a gateway in the LAN, which then decides how to route the "package" of data to the correct destination. Each gateway will need to keep track of which way to deliver various packages of data, and for this it uses a Routing Table. A routing table is a database which keeps track of paths, like a map, and allows the gateway to provide this information to the node requesting the information.
With hop-by-hop routing, each routing table lists, for all reachable destinations, the address of the next device along the path to that destination: the next hop. Assuming that the routing tables are consistent, the simple algorithm of relaying packets to their destination's next hop thus suffices to deliver data anywhere in a network. Hop-by-hop is the fundamental characteristic of the IP Internetwork Layer and the OSI Network Layer.
The primary function of a router is to forward a packet toward its destination network, which is the destination IP address of the packet. To do this, a router needs to search the routing information stored in its routing table.
A routing table is a data file in RAM that is used to store route information about directly connected and remote networks. The routing table contains network/next hop associations. These associations tell a router that a particular destination can be optimally reached by sending the packet to a specific router that represents the "next hop" on the way to the final destination. The next hop association can also be the outgoing or exit interface to the final destination.
The network/exit-interface association can also represent the destination network address of the IP packet. This association occurs on the router's directly connected networks.
A directly connected network is a network that is directly attached to one of the router interfaces. When a router interface is configured with an IP address and subnet mask, the interface becomes a host on that attached network. The network address and subnet mask of the interface, along with the interface type and number, are entered into the routing table as a directly connected network. When a router forwards a packet to a host, such as a web server, that host is on the same network as a router's directly connected network.
A remote network is a network that is not directly connected to the router. In other words, a remote network is a network that can only be reached by sending the packet to another router. Remote networks are added to the routing table using either a dynamic routing protocol or by configuring static routes. Dynamic routes are routes to remote networks that were learned automatically by the router, using a dynamic routing protocol. Static routes are routes to networks that a network administrator manually configured.
Difficulties with routing tables
The need to record routes to large numbers of devices using limited storage space represents a major challenge in routing table construction. In the Internet, the currently dominant address aggregation technology is a bitwise prefix matching scheme called Classless Inter-Domain Routing (CIDR).
Contents of routing tables
The routing table consists of at least three information fields:
the network id: i.e. the destination subnet
cost/metric: i.e. the cost or metric of the path through which the packet is to be sent
next hop: The next hop, or gateway, is the address of the next station to which the packet is to be sent on the way to its final destination
Depending on the application and implementation, it can also contain additional values that refine path selection:
quality of service associated with the route. For example, the U flag indicates that an IP route is up.
links to filtering criteria/access lists associated with the route
interface: such as eth0 for the first Ethernet card, eth1 for the second Ethernet card, etc.
Routing tables are also a key aspect of certain security operations, such as unicast reverse path forwarding (uRPF). In this technique, which has several variants, the router also looks up, in the routing table, the source address of the packet. If there exists no route back to the source address, the packet is assumed to be malformed or involved in a network attack, and is dropped.
Shown below is an example of what the table above could look like on an average computer connected to the internet via a home router:
The column Network Destination and Netmask together describe the Network id as mentioned earlier. For example, destination 192.168.0.0 and netmask 255.255.255.0 can be written as network id 192.168.0.0/24.
The Gateway column contains the same information as the Next hop, i.e. it points to the gateway through which the network can be reached.
The Interface indicates what locally available interface is responsible for reaching the gateway. In this example, gateway 192.168.0.1 (the internet router) can be reached through the local network card with address 192.168.0.100.
Finally, the Metric indicates the associated cost of using the indicated route. This is useful for determining the efficiency of a certain route from two points in a network. In this example, it is more efficient to communicate with the computer itself through the use of address 127.0.0.1 (called “localhost”) than it would be through 192.168.0.100 (the IP address of the local network card).
Forwarding Table
Routing tables are generally not used directly for packet forwarding in modern router architectures; instead, they are used to generate the information for a smaller forwarding table. A forwarding table contains only the routes which are chosen by the routing algorithm as preferred routes for packet forwarding. It is often in a compressed or pre-compiled format that is optimized for hardware storage and lookup.
This router architecture separates the Control Plane function of the routing table from the Forwarding Plane function of the forwarding table. This separation of control and forwarding provides uninterrupted performance.
How to Login Cisco Router
A. All routers have a built-in web-based setup page that allows you to customize settings and set up advanced properties.
Note: Before you access the web-based setup page of the router, make sure the router is powered on and the computer is wired to one of the Ethernet ports on the router, for example, 1, 2, 3 or 4.
Complete these steps:
Open a web browser such as Internet Explorer.
Go to the Address bar and enter the IP Address of your router then press Enter. For example,
192.168.15.1 is the default IP of most VOIP routers.
If the IP address of the router has been changed, type the IP address of the router in the Address bar instead.
The IP address of the router can be changed by these factors:
If you run the setup CD of the router
If you change it on the web-based setup page of the router
If you forgot the IP address of the router, you can try one of these steps:
Check the IP address of the router.
Press the Reset button at the back of the router for 30 seconds.
This procedure resets your router to factory defaults. Any settings on the router are erased. The IP address of the router will be 192.168.15.1 and the password is admin after you reset it.
A new window prompts for a User name and Password. Type admin for User name and Password, since admin is the default user name password, and then click OK.
If the password of the router has been changed, type the new password of the router in the Password field instead.
The password of the router can be changed by these factors:
If you run the setup CD of the router.
If you change it on the web-based setup page of the router.
Cisco Career Certifications
We offer five levels of network certification: Entry, Associate, Professional, Expert and Architect, the highest level of accreditation within the Cisco Career Certification program.
Not sure which certification to pursue? Explore the Career Guide.
Entry Certifications
Both the CCENT and the CCT certifications serve as starting points for individuals interested in starting a career as a networking professional.
CCENT
CCT
Associate Certifications
The Associate level of Cisco Certifications can begin directly with CCNA for network installation, operations and troubleshooting or CCDA for network design. Think of the Associate Level as the foundation level of networking certification.
CCDA
CCNA Cloud
CCNA Collaboration
CCNA Cyber Ops
CCNA Data Center
CCNA Industrial
CCNA Routing and Switching
CCNA Security
CCNA Service Provider
CCNA Wireless
Professional Certifications
The Professional level is an advanced level of certification that shows more expertise with networking skills. Each certification covers a different technology to meet the needs of varying job roles.
CCDP
CCNP Cloud
CCNP Collaboration
CCNP Data Center
CCNP Routing and Switching
CCNP Security
CCNP Service Provider
CCNP Wireless
Expert Certifications
The Cisco Certified Internetwork Expert (CCIE) certification is accepted worldwide as the most prestigious networking certification in the industry.
CCDE
CCIE Collaboration
CCIE Data Center
CCIE Routing and Switching
CCIE Security
CCIE Service Provider
CCIE Wireless
Architect Certification
Cisco Certified Architect is the highest level of accreditation achievable and recognizes the architectural expertise of network designers who can support the increasingly complex networks of global organizations and effectively translate business strategies into evolutionary technical strategies.
CCAr
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