Enhanced IGRP is enabled in Cisco IOS software using the router eigrp [ASN] global configuration command. The [ASN] keyword designates the EIGRP autonomous system number (ASN). This is a 32-bit integer between 1 and 65535. In addition to other factors, which will be described later in this lesson, routers running EIGRP must reside within the same autonomous system to form a neighbour relationship successfully. Following the configuration of the router eigrp [ASN] global configuration command, the router transitions to EIGRP Router Configuration mode wherein you can configure parameters pertaining to EIGRP. The configured ASN can be verified in the output of the show ip protocols command, as follows:
| R1#show ip protocolsRouting Protocol is “eigrp 150”Outgoing update filter list for all interfaces is not setIncoming update filter list for all interfaces is not set
Default networks flagged in outgoing updates Default networks accepted from incoming updates EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0 EIGRP maximum hopcount 100 EIGRP maximum metric variance 1
… |
In addition to the show ip protocols command, the show ip eigrp neighbors command prints information on all known EIGRP neighbours and their respective autonomous systems. This command, and its available options, will be described in detail later in this module. On routers running multiple instances of EIGRP, the show ip eigrp [ASN] command can be used to view information pertaining only to the autonomous system that is specified in this command. The use of this command is illustrated in the following output:
| R1#show ip eigrp 150 ?interfaces IP-EIGRP interfacesneighbors IP-EIGRP neighborstopology IP-EIGRP topology table
traffic IP-EIGRP traffic statistics |
In the output above, 150 is the ASN. The default in Cisco IOS software is to print information on all EIGRP instances if an autonomous system is not specified with any show ip eigrp commands.
Once in Router Configuration mode, the network command is used to specify the network(s) (interfaces) for which EIGRP routing will be enabled. When the network command is used and a major classful network is specified, the following actions are performed on the EIGRP-enabled router:
- EIGRP is enabled for networks that fall within the specified classful network range.
- The topology table is populated with these directly connected subnets.
- EIGRP Hello packets are sent out of the interfaces associated with these subnets.
- EIGRP advertises the network(s) to EIGRP neighbours in Update messages.
- Based on the exchange of messages, EIGRP routes are then added to the IP routing table.
For example, assume that the router has the following Loopback interfaces configured:
- Loopback0 – IP Address 10.0.0.1/24
- Loopback1 – IP Address 10.1.1.1/24
- Loopback2 – IP Address 10.2.2.1/24
- Loopback3 – IP Address 10.3.3.1/24
If EIGRP is enabled for use and the major classful 10.0.0.0/8 network is used in conjunction with the network router configuration command, all four Loopback interfaces are enabled for EIGRP routing. This is illustrated in the following output:
|
R1#show ip eigrp interfaces IP-EIGRP interfaces for process 150 Xmit Queue Mean Pacing Time Multicast Pending Interface Peers Un/Reliable SRTT Un/Reliable Flow Timer Routes Lo0 0 0/0 0 0/10 0 0 Lo1 0 0/0 0 0/10 0 0 Lo2 0 0/0 0 0/10 0 0 Lo3 0 0/0 0 0/10 0 0 |
You can use the show ip protocols command to verify that EIGRP is enabled for the major classful 10.0.0.0/8 network. The output of this command is illustrated below:
| R1#show ip protocolsRouting Protocol is “eigrp 150″Outgoing update filter list for all interfaces is not setIncoming update filter list for all interfaces is not set
Default networks flagged in outgoing updates Default networks accepted from incoming updates EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0 EIGRP maximum hopcount 100 EIGRP maximum metric variance 1 Redistributing: eigrp 150 EIGRP NSF-aware route hold timer is 240s Automatic network summarization is in effect Maximum path: 4 Routing for Networks: 10.0.0.0 Routing Information Sources: Gateway Distance Last Update
Distance: internal 90 external 170 |
The EIGRP topology table can be viewed using the show ip eigrp topology command. The output of this command is illustrated below:
| R1#show ip eigrp topologyIP-EIGRP Topology Table for AS(150)/ID(10.3.3.1)Codes: P – Passive, A – Active, U – Update, Q – Query, R – Reply,
r – reply Status, s – sia Status
P 10.3.3.0/24, 1 successors, FD is 128256 via Connected, Loopback3 P 10.2.2.0/24, 1 successors, FD is 128256 via Connected, Loopback2 P 10.1.1.0/24, 1 successors, FD is 128256 via Connected, Loopback1 P 10.0.0.0/24, 1 successors, FD is 128256 via Connected, Loopback0 |
NOTE: The topology table, EIGRP Hello packets, and Update messages are described in detail later in this module. The focus of this section is restricted to EIGRP configuration implementation.
Using the network command to specify a major classful network allows multiple subnets that fall within the classful network range to be advertised at the same time with minimal configuration. However, there may be situations where administrators may not want all of the subnets within a classful network to be enabled for EIGRP routing. For example, referencing the Loopback interfaces configured on R1 in the previous example, assume that you want EIGRP routing enabled only for the 10.1.1.0/24 and 10.3.3.0/24 subnets, and not for the 10.0.0.0/24 and 10.2.2.0/24 subnets. While it appears that this would be possible if you specified the networks (i.e., 10.1.1.0 and 10.3.3.0) when using the network command, Cisco IOS software still converts these statements to the major classful 10.0.0.0/8 network, as illustrated below:
| R1(config)#router eigrp 150R1(config-router)#network 10.1.1.0R1(config-router)#network 10.3.3.0R1(config-router)#exit |
Despite the configuration above, the show ip protocols command reveals the following:
| R1#show ip protocolsRouting Protocol is “eigrp 150″Outgoing update filter list for all interfaces is not setIncoming update filter list for all interfaces is not set
Default networks flagged in outgoing updates Default networks accepted from incoming updates EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0 EIGRP maximum hopcount 100 EIGRP maximum metric variance 1 Redistributing: eigrp 150 EIGRP NSF-aware route hold timer is 240s Automatic network summarization is in effect Maximum path: 4 Routing for Networks: 10.0.0.0 Routing Information Sources: Gateway Distance Last Update
Distance: internal 90 external 170 |
NOTE: A common misconception is that disabling the EIGRP automatic summarisation feature addresses this issue; however, this has nothing to do with the auto-summary command. For example, assume that you issued the no auto-summary command to the configuration used in the previous example, as follows:
| R1(config)#router eigrp 150R1(config-router)#network 10.1.1.0R1(config-router)#network 10.3.3.0R1(config-router)#no auto-summary
R1(config-router)#exit |
The show ip protocols command still shows that EIGRP is enabled for network 10.0.0.0/8, as illustrated below:
| R1#show ip protocolsRouting Protocol is “eigrp 150″Outgoing update filter list for all interfaces is not setIncoming update filter list for all interfaces is not set
Default networks flagged in outgoing updates Default networks accepted from incoming updates EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0 EIGRP maximum hopcount 100 EIGRP maximum metric variance 1 Redistributing: eigrp 150 EIGRP NSF-aware route hold timer is 240s Automatic network summarization is not in effect Maximum path: 4 Routing for Networks: 10.0.0.0 Routing Information Sources: Gateway Distance Last Update
Distance: internal 90 external 170 |
In order to provide more granular control of the networks that are enabled for EIGRP routing, Cisco IOS software supports the use of wildcard masks in conjunction with the network statement when configuring EIGRP. The wildcard mask operates in a manner similar to the wildcard mask used in ACLs and is independent of the subnet mask for the network.
As an example, the command network 10.1.1.0 0.0.0.255 would match the 10.1.1.0/24 network, the 10.1.1.0/26 network, and the 10.1.1.0/30 network. Referencing the Loopback interfaces configured in the previous output, R1 would be configured as follows to enable EIGRP routing for the 10.1.1.0/24 and 10.3.3.0/24 subnets, and not for the 10.0.0.0/24 subnet or the 10.2.2.0/24 subnet:
| R1(config)#router eigrp 150R1(config-router)#network 10.1.1.0 0.0.0.255R1(config-router)#network 10.3.3.0 0.0.0.255R1(config-router)#exit |
This configuration can be validated using the show ip protocols command, as follows:
| R1#show ip protocolsRouting Protocol is “eigrp 150″Outgoing update filter list for all interfaces is not setIncoming update filter list for all interfaces is not set
Default networks flagged in outgoing updates Default networks accepted from incoming updates EIGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0 EIGRP maximum hopcount 100 EIGRP maximum metric variance 1 Redistributing: eigrp 150 EIGRP NSF-aware route hold timer is 240s Automatic network summarization is in effect Maximum path: 4 Routing for Networks: 10.1.1.0/24 10.3.3.0/24 Routing Information Sources: Gateway Distance Last Update
Distance: internal 90 external 170 |
Additionally, the show ip eigrp interfaces command can be used to validate that EIGRP routing has been enabled only for Loopback1 and Loopback3:
|
R1#show ip eigrp interfaces IP-EIGRP interfaces for process 150 Xmit Queue Mean Pacing Time Multicast Pending Interface Peers Un/Reliable SRTT Un/Reliable Flow Timer Routes Lo1 0 0/0 0 0/10 0 0 Lo3 0 0/0 0 0/10 0 0 |
As illustrated in the output above, EIGRP routing is enabled only for Loopback1 and Loopback3 because of the wildcard mask configuration.
It is important to remember that the network command can be configured using the subnet mask, rather than the wildcard mask. When this is the case, Cisco IOS software inverts the subnet mask and the command is saved using the wildcard mask. For example, referencing the same Loopback interfaces on the router, R1 could also be configured as follows:
| R1(config-router)#router eigrp 150R1(config-router)#network 10.1.1.0 255.255.255.0R1(config-router)#network 10.3.3.0 255.255.255.0R1(config-router)#exit |
Based on this configuration, the following is entered in the running configuration (I’ve used a pipe to drill down to the part of config I’m interested in):
| R1#show running-config | begin router eigrprouter eigrp 150network 10.1.1.0 0.0.0.255network 10.3.3.0 0.0.0.255
auto-summary |
You can see by the above configuration that you can use pipes with show commands in order to get more granularity. This will be a familiar concept to anyone with previous programming knowledge.
If a specific address on the network is used, in conjunction with the wildcard mask, Cisco IOS software performs a logical AND operation to determine the network that will be enabled for EIGRP. For example, if the network 10.1.1.15 0.0.0.255 command is issued, Cisco IOS software performs the following actions:
- Inverts the wildcard mask to the subnet mask value of 255.255.255.0
- Performs a logical AND operation
- Adds the network 10.1.1.0 0.0.0.255 command to the configuration
The network configuration used in this example is illustrated in the following output:
| R1(config)#router eigrp 150R1(config-router)#network 10.1.1.15 0.0.0.255R1(config-router)#exit |
Based on this, the running configuration on the router displays the following:
| R1#show running-config | begin router eigrprouter eigrp 150network 10.1.1.0 0.0.0.255auto-summary |
If a specific address on the network is used in conjunction with the subnet mask, the router performs the same logical AND operation and adds the network command to the running configuration using the wildcard mask format. This is illustrated in the configuration below:
| R1(config)#router eigrp 150R1(config-router)#network 10.1.1.15 255.255.255.0R1(config-router)#exit |
Based on this configuration, the following is added to the current configuration on the router:
| R1#show running-config | begin router eigrprouter eigrp 150network 10.1.1.0 0.0.0.255auto-summary |
As illustrated in the configuration above, the use of either the wildcard mask or the subnet mask results in the same operation and network statement configuration in Cisco IOS software.
When configuring EIGRP in production networks, it is common practice to use a wildcard mask of all zeros or a subnet mask of all 1s. For example, the network 10.1.1.1 0.0.0.0 and network 10.1.1.1 255.255.255.255 commands perform the same actions. Using all zeros in the wildcard mask or all ones in the subnet mask configures Cisco IOS software to match an exact interface address, regardless of the subnet mask configured on the interface itself. Either one of these commands would match interfaces configured with the 10.1.1.1/8, 10.1.1.1/16, 10.1.1.1/24, and 10.1.1.1/30 address, for example. The use of these commands is illustrated in the following output:
The show ip protocols command verifies that the configuration of both network statements is treated in a similar manner on the router, as illustrated below:
When a subnet mask with all ones or a wildcard mask with all zeros is used, EIGRP is enabled for the specified (matched) interface and the network the interface resides on is advertised. In other words, EIGRP will not advertise the /32 address in the output above but, instead, the actual network based on the subnet mask configured on the matched interface. The use of this configuration is independent of the subnet mask configured on the actual interface matched.
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