Foundation Topics


Configuring EIGRP

The commands for EIGRP are consistent with the other IP routing protocols. Although IP routing is on automatically, the chosen routing protocol must be configured and the participating interfaces must be identified.

EIGRP allows for variable-length subnet mask (VLSM) and, therefore, summarization, because the mask is sent in the update packets. Although summarization is automatic, EIGRP summarizes at the IANA or major network boundary. To summarize within the IANA number, it must be manually configured. Unlike OSPF, which can summarize only at the area border router (ABR), EIGRP can summarize not only at any router, but also at any interface on any router.


EIGRP has evolved over the past few years . It is essential that, in a practical situation, you research the commands and configuration for the IOS software code level that is installed in your network.

This section covers the following:

  • Required commands for configuring EIGRP

  • Optional commands for EIGRP

  • Optional EIGRP commands specific to WANs

Required Commands for Configuring EIGRP

The router needs to understand how to participate in the EIGRP network. Therefore, it requires the following:

  • The EIGRP process The routing protocol needs to be started on the router.

  • The EIGRP autonomous system number All routers sharing routing updates and participating in the larger network must be identified as part of the same autonomous system. A router will not accept an update from a router configured with a different autonomous system number.

  • Participating router interfaces The router might not want to have all its interfaces to send or receive EIGRP routing updates. A classic example is a dialup line to a remote office. If there is only one subnet at the remote office, it would be more efficient to use default and static route commands, because any updates would dial the line.

By default (unless the setup script is used), there is no IP routing protocol running on the Cisco router. This is not true of other protocols, however. If an IPX network address is configured on an interface, for example, the IPX RIP process will be automatically started.

To configure EIGRP as the routing protocol, the following command syntax is used:

 Router(config)#  router eigrp   autonomous-system-number  

Although EIGRP has been turned on, it has no information about how to operate . The connected networks that are to be sent in the EIGRP updates and the interfaces that participate in the EIGRP updates must be defined. If the EIGRP information is not specified, the process with insufficient configuration will never start.


Most versions of the IOS software do not offer an error message when the configuration is incomplete, which can make troubleshooting more difficult. Refer to the section titled "Verifying the EIGRP Operation," later in this chapter for more information.

The following command syntax shows the use of the network command prior to Cisco IOS release 12.0(4)T:

 Router(config-router)#  network   network-number  

The network command in EIGRP plays a similar role to that of the network command in RIP or IGRP. Like OSPF, in which it is possible to identify the specific address of an interface, the network command for EIGRP can be stated with a mask option, allowing you to identify which interfaces are to run EIGRP. However, it is important to remember that EIGRP does not use areas. The ability to define the network mask was introduced in Cisco IOS release 12.04 (T).


A common error is to configure the network command with an inappropriate wildcard mask when you are confused as to which class of address is being used. Be sure to identify the correct wildcard mask to avoid the situation in which EIGRP only runs on some, if any, of the interfaces.

The new syntax is as follows :

 Router(config-router)#  network   network-number  [  wildcard-network-mask  ] Router(config-router)#  no network   network-number  [  wildcard-network-mask  ] 

The following syntax illustrates the use of the network command (the router has two Ethernet interfaces):

 Router(config)#  interface e1  Router(config-if)#  ip address  ! Router(config)#  interface e2  Router(config-if)#  ip address  

The following command indicates that EIGRP will run on interface e1 only:

 Router(config)#  router eigrp 100  Router(config-router)#  network  

In versions prior to the IOS release 12.04 (T), the network command acted differently. As soon as the first part of the command was configured, the operating system corrected the address to the Internet or major (classful) network number. In this case, example network would be connected to, which would include both e1 and e2.

After the network has been defined to EIGRP, it identifies the interfaces directly connected to the routers that share that network address. In some instances, it is not a good idea to have EIGRP updates running across certain interfaces, for example, links connecting to stub routers or to another routing protocol or autonomous system. Before 12.04(T), you would prevent EIGRP from sending updates through an interface by issuing the passive-interface command.

When a passive interface is created, it prevents Hellos from being sent between routers. This means that the routers cannot become neighbors, which results in no routing updates being either sent or received. However, the address of the interface is sent in updates out of nonpassive interfaces.

The passive interface allows the network address to be connected to stub routers (a typical frame relay hub-and-spoke configuration). The Ethernet network on the other side of the stub router might be included into the routing tables and propagated throughout the network, without using resources on the Ethernet link or on the router.

Once the interfaces on the router that are participating in the EIGRP domain using the network command are identified, the following happens:

  • Updates are received on the interface.

  • Updates are sent out the interfaces.

  • The network are advertised out all EIGRP interfaces.

  • If appropriate, the Hello protocol is propagated.

Optional Commands for Configuring EIGRP

The optional commands are used to tune the way EIGRP works within your network. They should be used in reference to the design of the network and its technical requirements.

This section considers the following optional EIGRP commands described in Table 14-2.

Table 14-2. Optional Commands for Configuring EIGRP



no auto-summary

Turns off auto summary, allowing the configuration of manual summarization.

ip summary-address

Manual configuration of summarization.

eigrp stub

Configures a stub router.


Configures unequal load balancing over multiple routes.

ip hello-interval eigrp autonomous-system-number seconds

Changes the number of seconds between Hellos.

ip hold-time eigrp autonomous-system-number seconds

Changes the length of time before a route is considered dead because the neighbor has not sent a Hello within the required time.


Changes the bandwidth setting on an interface, which affects the EIGRP metric calculation and the amount of EIGRP traffic that is sent through the interface.


Changes the amount of the bandwidth that EIGRP traffic can use. The default is 50%.

Summarization with EIGRP

Summarization in EIGRP solves the same scaling issues seen in other networks. The difference in the configuration between EIGRP and OSPF is that the OSPF is summarized only at the area boundary. Because EIGRP does not use the concept of areas, summarization can be configured on any router interface in the network. Consideration of where to summarize is determined by the hierarchical structure of the network. If summarization is not configured, EIGRP will automatically summarize at the class boundary.


Other chapters in this book have dealt with summarization in detail. For the sake of brevity, only those details related specifically to EIGRP are conveyed here. For more information about summarization, refer to Chapter 8, "Using OSPF Across Multiple Areas," and the sections "Design Considerations in Multiple Area OSPF" and "Summarization" in particular.

Summarization has advantages for EIGRP above and beyond the benefit of smaller routing tables, as explained in Chapter 13, "Using EIGRP in Enterprise Networks." Summarization reduces the amount of resources needed by both the network and the routers within the network. The reduced routing tables speed up the lookup when forwarding data that is process switched. Summarization also reduces the scope of the queries sent out by a router. If a router has no feasible successor, it queries its neighbor for an alternative route. If the neighbor has no route to offer, the query is forwarded on until a route is found or the search is exhausted. If summarization has been configured, the route that is being queried might have been summarized, and thus the query will end. Thus, summarization can limit the scope of the query, because when a subnet is hidden in summarization, a reply of unknown network will be returned to the router that can purge the route from the databases.

There are two commands for summarization with EIGRP: no auto-summary and ip summary-address eigrp autonomous-system-number address mask . The first command, no auto-summary , disables the automatic summarization. This command applies to the entire router. With no auto-summary configured, information on all the known subnets is sent out of every interface. If there are slow serial interfaces or congested links, these links could become overwhelmed. The solution is to configure the ip summary-address eigrp command on all interfaces, which in turn demands careful deployment of addresses.

Manual summarization is configured at the interface level, as shown here:

 Router(config)#  interface S0  Router(config-if)#  ip summary-address eigrp   autonomous-system-number address mask  
Stub Routers

IOS software release 12.0 made it possible for you to configure a remote router as an EIGRP stub router. A stub router is typically used on small capacity routers in a hub-and-spoke WAN environment. The stub router in EIGRP is similar to the concept of On Demand Routing (ODR) described in Chapter 1, "IP Routing Principles." ODR is used in similar situations but has no routing protocol configured on the stub router. ODR uses CDP to maintain connectivity between the stub routers and core router sending a default route to the stub. Stub routers in EIGRP networks use EIGRP to send limited information between the stub and the core routers.

As in ODR, the router in an EIGRP network has no other neighbors and accesses the network through a distribution layer router. It is not necessary, therefore, for this remote router to have a complete routing table that may overwhelm its limited resources. The remote router needs only a default route to the distribution router that can serve all its needs.

Another reason to configure the remote router as a stub is to lend a hand to the rest of the network. If a query is sent to a remote router, the delays involved can result in the path being Stuck in Active (SIA). If the stub configuration has been applied, the router responds to queries as inaccessible, thus limiting the scope of the query range and preventing SIA from occurring.

The following command structure shows the syntax of the eigrp stub command:

 Router(config-router)#  eigrp stub  [  receive-only   connected   static   summary  ] 

Table 14-3 explains the syntax of this command.

Table 14-3. The eigrp stub Command Syntax and Description




(Optional) Sets the router as a receive-only neighbor


(Optional) Advertises connected routes


(Optional) Advertises static routes


(Optional) Advertises summary routes

Figure 14-1 shows a group of routers connected over WAN links. These routers are stub routers because they have no other networks connected to them.

Figure 14-1. The eigrp stub Router Command


Example 14-1 is the configuration for Router B in Figure 14-1.

Example 14-1. The EIGRP Stub Router Command
 RouterB(config)#  router eigrp 100  RouterB(config-router)#  network  RouterB(config-router)#  eigrp stub  
Load Balancing in EIGRP

EIGRP automatically load balances across links of equal cost. Whether the traffic is sent on a per-destination or round- robin basis depends on the internal switching within the router. It is possible to configure EIGRP to load balance across unequal-cost paths using the variance command.

The variance command allows the administrator to identify the metric scope for including additional paths by the use of a multiplier parameter. The command structure follows:

 Router(config-router)#  variance   multiplier  

The multiplier argument is the metric value used for load balancing. It can be a value from 1 to 128. The default is 1, which means equal-cost load balancing.

Example 14-2 shows the configuration of the variance command.

Example 14-2. The variance Command
 RouterB(config)#  router eigrp 100  RouterB(config-router)#  network  RouterB(config-router)#  variance 2  

If the variance number is higher than the default of 1, the EIGRP process multiplies the best ( lowest ) cost or metric value for a path by the number stated as the variance multiplier. All paths to the same destination that have metrics within this new range are now included in load balancing. The amount of traffic sent over each link is proportional to the metric for the path.

For example, the route to Network A in Figure 14-2 has four paths to it from Router F, and the best path gave a metric value of 10. The available routes shown in Figure 14-2 reflect these paths:

F to E to A = 30

F to D to B = 15

F to C to B = 15

F to C to G = 10

Figure 14-2. Including Unequal Paths in Load Balancing



Only those paths that are in the topology table as feasible successor (FS) are eligible to be included in the variance command. Also, the example and figure shown are highly simplified for the purpose of explanation.

If the variance command was configured with a variance, or multiplier, of 2, the best metric is 10 * 2 = 20. Any route with a metric of 20 or better will be placed in the routing table.

These paths would all load-balance traffic from Router F to Network A:

F to D to B = 15

F to C to B = 15

F to C to G = 10

One-and-a-half packets would be sent across the path F to C to G for every one packet sent across the other two available paths.

The router rounds the number of packets to be sent to 2 packets, giving a traffic ratio of 3:2.

Tuning the EIGRP Process

There are many ways to tune a network, including load balancing across multiple paths, summarizing routes, and reducing the frequency of the update timers. There is, however, a trade-off between reducing the resources required to maintain the network and the stability of the network. The fewer Hellos that are sent out, for instance, the longer the network might take to notice a failure, and convergence of the network would be delayed. When the network does not have an accurate understanding of the available routes, the router cannot forward packets with any confidence.

The Hello timer and the receipt of ACKs are particularly important because EIGRP sends out incremental updates. The process sends updates only when a failure is seen or to advertise a new network, which makes it important to have a reliable and immediate method of noticing the link has died. Hence, reliable transport protocol (RTP) for EIGRP was created. Furthermore, it is the responsibility of the neighbor to first notice and then inform the rest of the network through an update that the network is no longer available.

You can configure the Hello timer, but you must consider how changing such a fundamental element impacts the accurate running of EIGRP. The hold timer indicates how long a route is held without a Hello being heard before the route is deemed to be no longer in existence. Both the Hello timer and the hold timer are discussed in the next sections.

The Hello Interval Timer

Tuning the Hello interval directly affects the ability of the network to notice a change in the state of a neighbor. Only after a router's interface is recognized as being down, or the router has failed to hear from a neighbor after a proscribed amount of time, does the router declare the neighbor dead and take the necessary action to update the routing table and the rest of the network.

For these reasons, the ip hello-interval eigrp command is typically used to decrease the time between Hellos to ensure that the network is more stable and converges more quickly. Although this increases the amount of bandwidth consumed, it is a minimal cost. This command becomes very useful in WANs, particularly when nonbroadcast multiaccess (NBMA) clouds are used. EIGRP treats both Frame Relay and Switched Multimegabit Data Service (SMDS) as NBMA technologies, resulting in Hello timers that assume a low bandwidth medium (less than T1 speeds) and that set the timer to 60 seconds by default.

The command to change how often the Hellos are sent to neighbors is as follows:

 Router(config-if)#  ip hello-interval eigrp   autonomous-system-number seconds  

The autonomous system number identifies the EIGRP process to the autonomous system.

The number of seconds to wait between each Hello is configured at the end of the command. An example of this configuration follows:

 Router(config)#  interface Serial 0  Router(config-if)#  ip hello-interval eigrp 100 10  

The defaults for Hello packet timers are as follows:

  • High bandwidth links (every 5 seconds):

    - Broadcast media, such as Ethernet, Token Ring, and FDDI

    - Point-to-point serial links, such as PPP or HDLC leased circuits, Frame Relay point-to-point subinterfaces, and ATM

    - Point-to-point subinterfaces

    - High bandwidth (greater than T1) multipoint circuits, such as ISDN PRI and Frame Relay

  • Low bandwidth links (every 60 seconds):

    - Multipoint circuits T1 bandwidth or slower, such as Frame Relay multipoint interfaces, ATM multipoint interfaces, and ATM

    - Switched virtual circuits and ISDN BRIs

The Hold Timer

The holdtime is how long the router waits without hearing a Hello from the neighbor before pronouncing it unavailable. The holdtime is three times that of the Hello timer by default, but changing the rate at which EIGRP sends Hello packets does not automatically change the holdtime. The hold timer must be changed manually using the ip hold-time eigrp command. The command syntax follows:

 Router(config-if)#  ip hold-time eigrp   autonomous-system-number seconds  

The following example shows the syntax in context:

 Router(config)#  interface ethernet 0  Router(config-if)#  ip hold-time eigrp 100 30  
Optional EIGRP Commands over WANs

There are always particular design and configuration issues concerning WANs. With WANs, more than at any other point in the network, you are likely to deal with limited resources. Therefore, it is with WAN topologies that you will use the bandwidth and bandwidth-percent commands, because they determine the link resources allocated to EIGRP updates and are used to calculate the metrics assigned to routes.

A perennial concern of network administrators is the amount of bandwidth used for overhead traffic. Administrators want to minimize the amount of network control traffic sent through the network to maximize the bandwidth available for user data. One of the major benefits of both EIGRP and OSPF is that they send as little network traffic as possible. This has the advantages of decreasing the convergence time of the network and ensuring that the network traffic that is sent arrives at the destination.

EIGRP Defaults in Bandwidth Utilization

EIGRP will not use more than 50 percent of the stated bandwidth on a link for its own routing traffic. The bandwidth command used on the interfaces of a Cisco router allows the default settings on links to work as intended, by stating the actual bandwidth of the link. This is often necessary on serial links because the default bandwidth is 1.544 Mbps or a T1. If in reality the link is 56 kbps, it is easy to see how EIGRP could saturate the link. EIGRP allows itself to use up to 50 percent of a T1 link (772 kbps), far exceeding the real bandwidth of the line. This could mean not only dropping data packets because of congestion but also dropping EIGRP packets. This will cause confusion in the network, not to mention miscalculated routes, retransmission, and user frustration as the network slows.

Other technologies, such as OSPF and SMDS on a Cisco router use the bandwidth value to make decisions. You need to ensure that the bandwidth stated is indeed the speed of the link. When you issue the show interface command, the configured bandwidth of the link will be shown along with a field identifying the load on the line. The load is the amount of traffic sent out of the interface, proportional to the bandwidth of the link, in which the bandwidth is the stated bandwidth and not the actual speed of the physical interface.


If it is necessary to artificially lower the bandwidth using the bandwidth command, this should be done in consideration of the other network applications.

The bandwidth is a logical construct whose value can have wide-reaching implications on the function of your network. It does not affect the actual speed of the link. In fact, it is practical to configure the bandwidth command only on serial lines, where the speed of the link will vary considerably. The following section provides further guidelines from Cisco on bandwidth configuration.

Rules in Configuring Bandwidth over an NBMA Cloud

EIGRP works well over all WAN environments, including point-to-point and NBMA such as Frame Relay, X25, or ATM. The NBMA topology can include either point-to-point subinterfaces or an NBMA hybrid, which is a combination of point-to-point and multipoint configurations.

Cisco identifies three rules that you should follow when configuring EIGRP over an NBMA cloud:

  • EIGRP traffic should not exceed the committed information rate (CIR) capacity of the virtual circuit (VC).

  • EIGRP's aggregated traffic over all the VCs should not exceed the access line speed of the interface.

  • The bandwidth allocated to EIGRP on each VC must be the same in both directions.

If you understand and follow these rules, EIGRP works well over the WAN. If you do not take care in the configuration of the WAN, EIGRP can swamp the network.

Configuring Bandwidth over a Multipoint Network

The configuration of the bandwidth command in an NBMA cloud depends on the design of the VCs. If the serial line has many VCs in a multipoint configuration, EIGRP will evenly distribute its overhead between the VCs, without the use of subinterfaces. The bandwidth command should therefore reflect the access link speed into the Frame Relay cloud. If the serial interface is accessing an NBMA environment such as Frame Relay, the situation is straightforward. Your company might have five VCs from your router's serial interface, each carrying 56 kbps. The access link will need a capacity of 5 * 56 kbps. Remember, the aggregate configured bandwidth cannot exceed the access speed of the interface.

Configuring Bandwidth over a Hybrid Multipoint Network

If the multipoint network has differing speeds allocated to the VCs, a more complex solution is needed. There are two main approaches:

  • Take the lowest CIR and simply multiply it by the number of circuits. This is applied to the physical interface. The problem with this configuration is that the higher-bandwidth links will be underutilized for some things.

  • If possible, it is much easier to configure and manage an environment that has used subinterfaces, where a VC is logically treated as if it were a separate interface or point-to point. The bandwidth command can be configured on each subinterface, which allows different speeds on each VC. In this solution, subinterfaces are configured for the links with the differing CIRs. The links that have the same configured CIR are presented as a single subinterface with a bandwidth, which reflects the aggregate CIR of all the circuits.

    Cisco recommends this as the preferred solution.

The following syntax shows the structure of the bandwidth command:

 Router#  interface S0  Router(config-if)#  bandwidth   speed-of-line  
Configuring the Pure Point-to-Point Network

If there are many VCs, there might not be enough bandwidth at the access speed of the interface to support the aggregate EIGRP traffic. The subinterfaces should be configured with a bandwidth that is much lower than the real speed of the circuit. In this case, it is necessary to use the bandwidth-percent command to indicate to the EIGRP process that it can still function.

As you learned in the previous section, EIGRP limits itself to 50 percent of the value specified in the bandwidth command, or if the bandwidth command is not set, the interface defaults. If you need to limit this percentage further, the upper limit that EIGRP uses can be stated as a percentage of the bandwidth command.

The ip bandwidth-percent-eigrp command interacts with the bandwidth command on the interface. You would use this command primarily because in your network, the bandwidth command does not reflect the true speed of the link. The bandwidth command might have been altered to manipulate the routing metric and path selection of a routing protocol, such as IGRP or OSPF. It might be better to use other methods of controlling the routing metric and return the bandwidth to a true value. Otherwise, the ip bandwidth-percent eigrp command is available. It is possible to set a bandwidth percent that is larger than the stated bandwidth. This is with the understanding that, although the bandwidth might be stated to be 56 kbps, the link is in fact 256 kbps. The following shows the structure of the ip bandwidth-percent eigrp command:

 Router(config)#  interface S0  Router(config-if)#  ip bandwidth-percent eigrp   autonomous-system-number percent  

Verifying the EIGRP Operation

Understanding the output of the commands discussed in this section is important, not just because they might constitute questions on the exam, but because they reflect your conceptual understanding of the subject. The ability to analyze what is happening on the network demands a thorough understanding of the concepts explained in this chapter. This skill is required in interpreting the output of a show command.

The ability to interpret these show command output examples in conjunction with the physical and logical topology diagrams of your organization will ensure your understanding of the operation of EIGRP.

This section deals with the show commands shown in Table 14-4.

Table 14-4. EIGRP show Commands

Command Option


show ip eigrp neighbors

Gives detailed information about the neighbors. This command records the communication between the router and the neighbors in addition to the interface and address by which they communicate.

show ip eigrp topology

Gives details about the routes held in the topology table, detailed information on the networks that the router is aware of and the preferred paths to those networks, and the next logical hop as the first step in the path. The router will track the EIGRP packets that have been sent to neighbors in this table.

show ip eigrp topology all-links

Gives details about all the routes and alternative paths held in the topology table. The router will track the EIGRP packets that have been sent to neighbors in this table.

show ip eigrp traffic

Gives information about the aggregate traffic sent to and from the EIGRP process.

The EIGRP show commands are highly detailed and give a comprehensive understanding of the state of the network. The other commands generic to IP show ip route and show ip protocols , as described in Chapter 7, "Configuring OSPF in a Single Area"are also useful in the maintenance of EIGRP.

The show ip eigrp neighbors Command

This show ip eigrp neighbors command shows the neighbor table. The syntax is as follows:

 Router#  show ip eigrp neighbors  [  type number  ] 

Example 14-3 shows the output of this command.

Example 14-3. The show ip eigrp neighbors Output
 Router#  show ip eigrp neighbors  IP-EIGRP Neighbors for process 100 Address          interface    Holdtime   Uptime    Q      Seq      SRTT      RTO                               (secs)     (h:m:s)   Count  Num      (ms)      (ms)    Ethernet1    13         0:00:41   0      11       4         20    Ethernet0    14         0:02:01   0      10       12        24    Ethernet0    12         0:02:02   0      4        5         2 

Table 14-5 explains the meaning of the important fields in Example 14-3.

Table 14-5. Explanation of the show ip eigrp neighbors Command Results



Process 100

The autonomous system number used to identify routers from whom to accept routing updates.


IP address of the EIGRP neighbor.


Interface on which the router is receiving Hello packets from the neighbor.


Length of time, in seconds, that the router will wait to hear from the neighbor before declaring it down. The default is 15 seconds.


Timemeasured in hours, minutes, and secondssince the router first heard from this neighbor.

Q Count

Number of EIGRP packets (update, query, and reply) that the router has queued and is waiting to send.

Seq Num

The sequence number of the last packet that was received from the neighbor.


Smooth round-trip time. The time is measured in milliseconds and is measured from the sending of the packet to the receipt of an acknowledgment from the neighbor.


Retransmission timeout, in milliseconds. This shows how long the router will wait for an acknowledgment before it retransmits the packet.

The show ip eigrp topology Command

The show ip eigrp topology command shows the topology table. This command allows for the analysis of DUAL. It shows whether the successor or the route is in an active or passive state. The syntax is as follows:

 Router#  show ip eigrp topology  [  autonomous-system-number  [[  ip-address  ]  mask  ]] 

Example 14-4 shows the output of this command.

Example 14-4. The show ip eigrp topology Output
 Router#  show ip eigrp topology  IP-EIGRP Topology Table for process 100 Codes:P - Passive, A  Active, U - Update, Q - Query, R - Reply, r  Reply status P, 2 successors, FD is 0 via (46251776/46226176), Ethernet0 via (46251776/46226176), Ethernet1 via (46277376/46251776), Ethernet0 P, 1 successors, FD is 307200 via Connected, Ethernet1 via (307200/281600), Ethernet1 (307200/281600), Ethernet0 via (332800/307200), Ethernet0 

Table 14-6 explains the meaning of the important fields in Example 14-4.

Table 14-6. Explanation of the show ip eigrp topology Command Results




Passive The router has not received any EIGRP input from a neighbor, and the network is assumed to be stable.


Active When a route or successor is down, the router attempts to find an alternative path. After local computation, the router realizes that it must query the neighbor to see whether it can find a feasible successor or path.


Update A value in this field identifies that the router has sent an update packet to a neighbor.


Query A value in this field identifies that the router has sent a query packet to a neighbor.


Reply A value here shows that the router has sent a reply to the neighbor.


This is used in conjunction with the query counter; the router has sent out a query and is awaiting a reply.

This is the destination IP network number.

This is the destination subnet mask.


This is the number of routes or the next logical hop. The number stated here is the same as the number of applicable routes in the routing table.


Feasible distance This is the metric or cost to the destination from the router.


This is the number of replies that the router is still waiting for from this neighbor. This is relevant only when the route is in an active state and is therefore not shown in Example 14-4.


This is the EIGRP state of the route. It can be the number 0, 1, 2, or 3. This is relevant when the destination is active and is therefore not shown in Example 14-4.


This is the address of the next logical hop, or the neighbor that told the router about this route. The first N s of these entries are the current successors. The remaining entries on the list are feasible successors.


The first number is the EIGRP metric that represents the feasible distance, or the cost to the destination. The number after the slash is the EIGRP metric that the peer advertised, or the advertised distance.


This is the interface through which the EIGRP packets were received and, therefore, is the outgoing interface.

The show ip eigrp traffic Command

The show ip eigrp traffic command shows the EIGRP traffic received and generated by the router. The following is the command syntax:

 Router#  show ip eigrp traffic  [  autonomous-system-number  ] 

Example 14-5 shows the output of this command.

Example 14-5. The show ip eigrp traffic Command Output
 Router#  show ip eigrp traffic  IP-EIGRP Traffic Statistics for process 100 Hellos sent/received: 218/205 Updates sent/received: 7/23 Queries sent/received: 2/0 Replies sent/received: 0/2 Acks sent/received: 21/14 

Table 14-7 explains the meaning of the important fields in Example 14-5.

Table 14-7. Explanation of the show ip eigrp traffic Command Output



process 100

The autonomous system number, used to identify routers from whom to accept routing updates

Hellos sent/received

Number of Hello packets sent and received by the router

Updates sent/received

Number of update packets sent and received by the router

Queries sent/received

Number of query packets sent and received by the router

Replies sent/received

Number of reply packets sent and received by the router

Acks sent/received

Number of acknowledgment packets sent and received by the router

Troubleshooting the EIGRP Operation

Many methods and tools help in troubleshooting any network. One of the main keys is documentation, for several reasons: For example, you can see progress and easily eliminate the obvious in a checklist manner, and you can clearly explain the problem and the steps taken so far in solving it if you need to call in expert help. Cisco provides many tools both on its web page and in service contracts to help solve your network problems. One of the mainstays in troubleshooting any routing protocol is the group of debug commands, which provide the ability to see traffic and router processes in real time.

Care should be exercised in the use of the debug command, because it can be very greedy in terms of the resources that it consumes. It should be used only for a specific option and for a finite time.

The options available for monitoring EIGRP are covered in Table 14-8.

Table 14-8. The debug Command Options for EIGRP

Command Option


debug eigrp packet

Shows the packets sent and received by the router. The packet types to be monitored can be selected. Up to 11 types are available.

debug eigrp neighbors

Shows the Hello packets sent and received by the router and the neighbors discovered by this process.

debug ip eigrp route

The default if the command debug ip eigrp is issued. Shows dynamic changes made to the routing table.

debug ip eigrp summary

Shows the process taken when a summary (manual or auto) is changed on the router.

CCNP BSCI Exam Certification Guide
CCNP BSCI Exam Certification Guide (CCNP Self-Study, 642-801) (3rd Edition)
ISBN: 1587200856
EAN: 2147483647
Year: 2002
Pages: 194
Authors: Clare Gough © 2008-2017.
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