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Enable the EIGRP process


EIGRP uses theR1(config)# router eigrp autonomous-system command to enable the EIGRP process. Then you get the R1(config-router)# prompt.

The autonomous system number referred to in the EIGRP configuration is not associated with the Internet Assigned Numbers Authority (IANA) globally assigned autonomous system numbers used by external routing protocols.

The autonomous-system argument can be assigned to any 16-bit value between the number 1 and 65,535. All routers within the EIGRP routing domain must use the same autonomous system number.

Autonomous system number

The guidelines for the creation, selection, and registration of an autonomous system are described in RFC 1930. Global autonomous system numbers are assigned by IANA, the same authority that assigns IP address space.

Usually Internet Service Providers (ISPs), Internet backbone providers, and large institutions connecting to other entities require an autonomous system number. These ISPs and large institutions use the exterior gateway routing protocol, Border Gateway Protocol (BGP), to propagate routing information. BGP is the only routing protocol that uses an actual autonomous system number in its configuration.

The vast majority of companies and institutions with IP networks do not need an autonomous system number, because they are controlled by a larger entity, such as an ISP. These companies use interior gateway protocols, such as RIP, EIGRP, OSPF, and IS-IS to route packets within their own networks. They are one of many independent and separate networks within the autonomous system of the ISP. The ISP is responsible for the routing of packets within its autonomous system and between other autonomous systems.

The autonomous system number used for EIGRP configuration is only significant to the EIGRP routing domain. It functions as a process ID to help routers keep track of multiple, running instances of EIGRP. This is required because it is possible to have more than one instance of EIGRP running on a network. Each instance of EIGRP can be configured to support and exchange routing updates for different networks.

Note: Both EIGRP and OSPF can support multiple instances of each routing protocol, although this type of multiple routing protocol implementation is not usually needed or recommended.

The router eigrp autonomous-system command does not start the EIGRP process itself. The router does not start sending updates. Rather, this command only provides access to configure the EIGRP settings.

Disable:  To completely remove the EIGRP routing process from a device, use the no router eigrp autonomous-system global configuration mode command, which stops the EIGRP process and removes all existing EIGRP router configurations.

Router ID

In EIGRP IPv4 implementations, the use of the router ID is not that apparent. EIGRP for IPv4 uses the 32-bit router ID to identify the originating router for redistribution of external routes. The need for a router ID becomes more evident in the discussion of EIGRP for IPv6. The router ID is necessary for redistribution.

Cisco routers derive the router ID based on three criteria, in the following precedence:

1. Use the IPv4 address configured with the eigrp router-id router configuration mode command.

2. If the router ID is not configured, the router chooses the highest IPv4 address of any of its loopback interfaces.

3. If no loopback interfaces are configured, the router chooses the highest active IPv4 address of any of its physical interfaces.

Some versions of IOS will accept the command router-id, without first specifying eigrp. The running-config, however, will display eigrp router-id regardless of which command is used.


The network command has the same function as in all IGP routing protocols. The network command in EIGRP:

  • Enables any interface on this router that matches the network address in the network router configuration mode command to send and receive EIGRP updates.
  • The network of the interfaces is included in EIGRP routing updates.

1, classful

Router(config-router)# network ipv4-network-address

The ipv4-network-address argument is the classful IPv4 network address for this interface.

2, classless

To configure EIGRP to advertise specific subnets only, use the wildcard-mask option with the network command:

Router(config-router)# network network-address [wildcard-mask]


Use wildcard mask or not?  

For example, we have two interfaces active on a router:



To turn on EIGRP on interface F0/0, we can use

router eigrp 1



The answer is: we can use wildcard masks or not, it does not matter. Not having a wildcard mask does not make the routes conflicting. The “network …” command in EIGRP (and OSPF, RIP) does not means “advertise this network” but means “If I has interface(s) belongs to this network please turn on EIGRP on that interface. Therefore when you don’t use wildcard mask EIGRP will turn on EIGRP on all interfaces that belongs to the network you specify in the “network …” command.

You should only use wildcard mask on EIGRP if you have 2 or more interfaces that belong to the same major networks but you don’t want to run EIGRP on all of them. For example if your router has 2 interfaces whose IP addresses are and but you only want to run EIGRP on the first interface, you can type “network” under EIGRP process.

Note: Prior to IOS 15, EIGRP automatic summarization was enabled by default. To disable it, using the no auto-summary router configuration mode command:

Router(config-router)# no auto-summary

Log neighbour change


By default, the eigrp log-neighbor-changes router configuration mode command is enabled. This command is used to:

  • Display any changes in EIGRP neighbor adjacencies.
  • Help verify neighbor adjacencies during configuration of EIGRP.
  • Advise the network administrator when any EIGRP adjacencies have been removed.
Passive interface


Router(config-router)# passive-interface interface-type interface-number

Verify the EIGRP process

1, show ip protocols: show parameters and current state of any active routing protocols, displays different types of output specific to each routing protocol

2, show ip eigrp neighbors

output includes:

  • H column(handle) – Lists the neighbors in the order that they were learned. Here you will find the order when the neighbor adjacency was established. Your first neighbor will have a value of 0, the second neighbor a value of 1 and so on.
  • Address – IPv4 address of the neighbor.
  • Interface – Local interface on which this Hello packet was received.
  • Hold – Current hold time. When a Hello packet is received, this value is reset to the maximum hold time for that interface, and then counts down to zero. If zero is reached, the neighbor is considered down. The default holddown timer is 15 seconds. On older IOS versions only a hello packet would reset the holddown timer but on newer IOS versions any EIGRP packet after the first hello will reset the holddown timer.
  • Uptime – Amount of time since this neighbor was added to the neighbor table.
  • Smooth Round Trip Timer (SRTT) and Retransmission Timeout (RTO) – Used by RTP to manage reliable EIGRP packets.
  • SRTT (Smooth round-trip time): The number of milliseconds it takes to send an EIGRP packet to your neighbor and receive an acknowledgment packet back.
  • RTO (Retransmission timeout): The amount of time in milliseconds that EIGRP will wait before retransmitting a packet from the retransmission queue to this neighbor.
  • Q Cnt (Queue Count) – The number of EIGRP packets (Update, Query or Reply) in the queue that are awaiting transmission. Ideally you want this number to be 0 otherwise it might be an indication of congestion on the network. If more than zero, then EIGRP packets wait to be sent.
  • Seq Num (Sequence Number) – Used to track updates, queries, and reply packets you received from your EIGRP neighbor.

3, show ip interface brief

4, show ip route command. EIGRP routes are denoted in the routing table with a D. The letter D was used to represent EIGRP because the protocol is based upon the DUAL algorithm.