PART 8: EIGRP Static Neighbors

Enhanced Interior Gateway Routing Protocol

Enhanced Interior Gateway Routing Protocol (EIGRP) is typically considered a dynamic routing protocol, automatically discovering neighbors and exchanging routes. However, EIGRP also offers static neighbor functionality, creating an interesting hybrid between dynamic and static routing protocols.

Dynamic vs. Static Neighbor Discovery

Most dynamic routing protocols operate on these principles:

1. Automatically discover neighboring routers

2. Dynamically exchange routing information

3. Calculate optimal paths using protocol-specific algorithms

In standard EIGRP deployments, routers find neighbors by sending Hello packets to the multicast address 224.0.0.10. This allows for automatic discovery without manual configuration of peer relationships.

EIGRP Static Neighbor Functionality

EIGRP's static neighbor feature enables you to explicitly define neighbor relationships, similar to BGP's neighbor configuration model. When configured:

1. EIGRP switches from multicast to unicast communication with the specified neighbor

2. Hello packets and all other EIGRP messages are sent directly to the configured neighbor's IP address

3. Each neighbor must be individually defined with its specific IP address
   

Use Cases for Static Neighbors

The primary scenarios where static neighbors prove valuable include:

1. Non-Broadcast Networks: When the underlying network doesn't support multicast or broadcast traffic

2. Frame Relay Hub-and-Spoke: In hub-and-spoke topologies where direct communication between spokes is desired

3. Security Requirements: When multicast traffic is filtered for security reasons

4. DMVPN Environments: To control neighbor relationships in Dynamic Multipoint VPN deployments

5. Troubleshooting: For isolating specific neighbor relationships during network debugging
   

Configuration Commands

Cisco IOS/IOS XE (Numbered Mode)

Router(config)# router eigrp <AS-NUMBER>
Router(config-router)# neighbor <IP-ADDRESS> <OUTGOING-INTERFACE>

Cisco IOS XE (Named Mode)

Router(config)# router eigrp <PROCESS-NAME>
Router(config-router)# address-family ipv4 autonomous-system <AS-NUMBER>
Router(config-router-af)# neighbor <IP-ADDRESS> <OUTGOING-INTERFACE>

Cisco IOS XR

Router(config)# router eigrp <PROCESS-NAME>
Router(config-eigrp)# address-family ipv4
Router(config-eigrp-af)# interface <INTERFACE-NAME>
Router(config-eigrp-af-if)# neighbor <IP-ADDRESS>

Considerations and Limitations

When implementing static neighbors, be aware of these important considerations:

1. Bidirectional Configuration: Static neighbor relationships must be configured on both routers

2. Multicast Suppression: Interfaces with static neighbors configured will no longer send multicast Hello packets

3. Multiple Neighbors: Each static neighbor requires its own configuration line

4. Interface Specification: You must specify the outgoing interface to reach each neighbor

5. Mixed Environments: You can mix static and dynamic neighbors in the same EIGRP domain
   

Operational Differences

With static neighbors:

• All EIGRP packets (Hellos, Updates, Queries, Replies) are unicast

• The underlying routing process remains unchanged

• Route calculation, metrics, and DUAL algorithm operate normally

• Only the neighbor discovery mechanism changes from dynamic to manual
  

Verification

To verify static neighbor relationships:

Router# show ip eigrp neighbors details           #IOS XE
Router# show  eigrp neighbors details             #IOS XR

The output will show these neighbors just like dynamically discovered ones, though they are established through the static configuration.

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