show ip eigrp neighbors
Verify EIGRP neighbour adjacencies are established and diagnose why neighbours are not forming or are flapping.
Definition: show ip eigrp neighbors is a Cisco IOS privileged exec command. Displays all EIGRP neighbours with their addresses, interfaces, hold time, uptime, SRTT (smooth round-trip time), RTO, queue count, and sequence numbers.
Overview
The 'show ip eigrp neighbors' command is a fundamental diagnostic tool in Cisco IOS that displays the EIGRP neighbor table. This command is essential for verifying that EIGRP adjacencies have formed correctly and for troubleshooting neighbor relationship issues. EIGRP (Enhanced Interior Gateway Routing Protocol) is a Cisco proprietary distance-vector routing protocol that uses the Diffusing Update Algorithm (DUAL) to ensure loop-free and fast convergence.
The neighbor table is the foundation of EIGRP operation; without established neighbors, routes cannot be exchanged. Network engineers reach for this command when they suspect adjacency problems, such as mismatched K-values, authentication failures, or hold-time expiration. It is often the first step in EIGRP troubleshooting, preceding 'show ip eigrp topology' or 'show ip route eigrp'.
The command requires privileged EXEC mode (enable) and does not modify the running configuration. Output is typically displayed in a tabular format, and if the neighbor table is large, it may be buffered or paginated. Understanding the output fields—such as Hold time, Uptime, SRTT, RTO, and Q Count—is critical for diagnosing issues like flapping neighbors or high packet loss.
This command is also useful for verifying that the correct interfaces are participating in EIGRP and that the router is communicating with the expected peers.
show ip eigrp neighbors [interface-id] [detail]When to Use This Command
- Confirm EIGRP neighbours have formed after enabling EIGRP routing
- Diagnose neighbour flapping — uptime resets indicate the adjacency is repeatedly dropping
- Check hold time countdown — if it reaches 0, the neighbour is declared dead
- Identify neighbours with high SRTT values indicating poor WAN link quality
Parameters
| Parameter | Syntax | Description |
|---|---|---|
| interface | interface-type interface-number | Specifies a particular interface to display neighbors learned through that interface. For example, 'GigabitEthernet0/0'. If omitted, all EIGRP neighbors are shown. Common mistake: using the wrong interface name or number, resulting in no output. |
| vrf | vrf vrf-name | Displays neighbors for a specific VRF instance. Used in MPLS/VPN or multi-VRF environments. If omitted, neighbors in the default VRF are shown. Common mistake: forgetting to specify the VRF when troubleshooting a VRF-specific issue. |
Command Examples
EIGRP neighbour table
Router# show ip eigrp neighbors
EIGRP-IPv4 Neighbors for AS(100)
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
0 10.0.0.2 Gi0/0 14 00:05:43 12 200 0 45
1 192.168.1.2 Gi0/1 12 00:12:15 8 200 0 67Understanding the Output
H = handle (internal ID). Hold = seconds until neighbour is declared dead if no hello received (default 15s). SRTT = smooth round-trip time in milliseconds.
RTO = retransmission timeout (SRTT × 6). Q Cnt = outstanding unacknowledged updates (non-zero means congestion or unreachable neighbour). Seq Num = last sequence number received.
Configuration Scenarios
Verify EIGRP adjacency between two routers
Two routers, R1 and R2, are connected via a serial link. EIGRP has been configured on both, but routes are not being exchanged. The engineer needs to verify that the neighbor adjacency has formed.
Topology
R1(Se0/0/0)---10.0.12.0/30---(Se0/0/0)R2Steps
- 1.Step 1: On R1, enter privileged EXEC mode: enable
- 2.Step 2: Display EIGRP neighbors: show ip eigrp neighbors
- 3.Step 3: Check if R2's IP address (10.0.12.2) appears in the neighbor table with a state of 'Init' or 'Pending' (if not fully established).
- 4.Step 4: If no neighbors are shown, verify EIGRP configuration on both routers and check interface status.
! On R1: interface Serial0/0/0 ip address 10.0.12.1 255.255.255.252 ! router eigrp 100 network 10.0.12.0 0.0.0.3 ! ! On R2: interface Serial0/0/0 ip address 10.0.12.2 255.255.255.252 ! router eigrp 100 network 10.0.12.0 0.0.0.3
Verify: show ip eigrp neighbors Expected output on R1: H Address Interface Hold Uptime SRTT RTO Q Seq (sec) (ms) Cnt Num 0 10.0.12.2 Se0/0/0 13 00:01:23 1 100 0 5
Watch out: Ensure both routers use the same EIGRP autonomous system number (ASN). A mismatch will prevent adjacency.
Troubleshoot EIGRP neighbor flapping due to authentication mismatch
A network administrator notices that the EIGRP neighbor between two routers is flapping (going up and down). The cause is suspected to be a mismatch in MD5 authentication configuration.
Topology
R1(Gi0/0)---192.168.1.0/30---(Gi0/0)R2Steps
- 1.Step 1: On R1, enter privileged EXEC mode: enable
- 2.Step 2: Display EIGRP neighbors with detailed output: show ip eigrp neighbors detail
- 3.Step 3: Look for the 'Auth' field; if authentication is enabled, it will show 'MD5' or 'SHA'. If one router has authentication and the other does not, the neighbor state may show 'Init' or 'Pending'.
- 4.Step 4: Check the hold time and uptime; if uptime resets frequently, authentication mismatch is likely.
- 5.Step 5: Verify authentication configuration on both routers.
! On R1: key chain EIGRP_KEY key 1 key-string cisco123 ! interface GigabitEthernet0/0 ip authentication mode eigrp 100 md5 ip authentication key-chain eigrp 100 EIGRP_KEY ! ! On R2 (correct configuration): key chain EIGRP_KEY key 1 key-string cisco123 ! interface GigabitEthernet0/0 ip authentication mode eigrp 100 md5 ip authentication key-chain eigrp 100 EIGRP_KEY
Verify: show ip eigrp neighbors detail Expected output on R1: H Address Interface Hold Uptime SRTT RTO Q Seq (sec) (ms) Cnt Num 0 192.168.1.2 Gi0/0 13 00:05:00 1 100 0 5 Version 2, Auth: MD5, key-id: 1 If authentication mismatches, the neighbor may not appear or uptime will be very low.
Watch out: The key chain name and key string must match exactly. Also, the authentication mode must be consistent (MD5 or SHA).
Troubleshooting with This Command
When troubleshooting EIGRP neighbor issues, the 'show ip eigrp neighbors' command is your first line of defense. A healthy neighbor table shows all expected peers with a state of 'Init' or 'Pending' (briefly) and then 'Up'. The 'Hold' column indicates the remaining time before the neighbor is declared dead (default 15 seconds).
If the hold time repeatedly drops to 0 and the neighbor disappears, you have a flapping issue. Focus on the 'Uptime' field: a low uptime (seconds or minutes) suggests recent adjacency loss. The 'SRTT' (Smooth Round Trip Time) and 'RTO' (Retransmission Timeout) values indicate link quality; high SRTT or RTO may point to congestion or high latency.
The 'Q Count' should be 0; a non-zero value indicates packets are queued for transmission, possibly due to a slow link or CPU overload. The 'Seq Num' is the sequence number of the last EIGRP packet received; if it jumps unexpectedly, packets may be lost. Common symptoms: no neighbors at all (check interface status, EIGRP configuration, ASN mismatch, passive interface, or ACL blocking EIGRP multicast 224.0.0.10).
Partial neighbor table (some peers missing) may indicate a Layer 2 issue or authentication mismatch. Flapping neighbors often result from mismatched K-values, hold timers, or authentication. Step-by-step diagnostic flow: 1) Run 'show ip eigrp neighbors' to see if any neighbors exist. 2) If none, check 'show ip eigrp interfaces' to verify EIGRP is active on the correct interfaces. 3) Use 'debug eigrp packets' (with caution) to see if hello packets are exchanged. 4) Correlate with 'show ip interface brief' to ensure interfaces are up/up. 5) Check 'show ip eigrp topology' to see if routes are learned. 6) If neighbors appear but routes are missing, verify route filtering or summarization.
The command output can be correlated with 'show logging' to see adjacency change messages. For persistent issues, use 'show ip eigrp neighbors detail' to see authentication and version details.
CCNA Exam Tips
CCNA exam: EIGRP neighbour requirements — same AS number, same K-values (metric weights), authentication if configured, reachable network
Hold time defaults to 15s (3 × hello interval of 5s on LAN, 60s hold on WAN)
If Q Cnt stays non-zero, the neighbour is not acknowledging updates — indicates a connectivity problem
Common Mistakes
Configuring EIGRP on both ends with different AS numbers — neighbours will not form
Mismatched K-values (default K1=K3=1, K2=K4=K5=0) prevent adjacency
Expecting EIGRP to form through an ACL that blocks EIGRP traffic (uses IP protocol 88)
show ip eigrp neighbors vs show ip route
These commands are often confused because both pertain to routing in EIGRP environments, but 'show ip eigrp neighbors' focuses on neighbor adjacency details, while 'show ip route' displays the resulting routing table entries and their sources. Understanding their distinct purposes is key to efficient troubleshooting.
| Aspect | show ip eigrp neighbors | show ip route |
|---|---|---|
| Scope | Neighbor adjacency | Entire routing table |
| Information Provided | Neighbor address, interface, hold time, uptime, SRTT, RTO, queue, sequence | Prefix, next-hop, AD, metric, source protocol, outgoing interface |
| Layer | EIGRP protocol layer (Layer 3) | IP routing table (Layer 3) |
| Use Case | Troubleshooting neighbor relationships | Verifying route reachability and selection |
| Output Format | Tabular per neighbor | Hierarchical per prefix with subnets |
| Protocol Specificity | EIGRP-specific | Multi-protocol (OSPF, BGP, static, etc.) |
Use show ip eigrp neighbors when verifying EIGRP neighbor adjacencies and their health metrics.
Use show ip route when inspecting the overall routing table to determine which routes are installed and their next-hop paths.
Platform Notes
In IOS-XE (e.g., Catalyst 9000 switches), the command syntax is identical to classic IOS. However, output may include additional fields like 'Interface' in a different format (e.g., 'GigabitEthernet1/0/1'). On NX-OS (Nexus switches), the equivalent command is 'show ip eigrp neighbors' but with slightly different output formatting; NX-OS also supports 'show ip eigrp neighbors vrf all' to display neighbors across all VRFs.
On ASA firewalls, EIGRP is not supported; use 'show route' or 'show ospf neighbors' instead. In IOS-XR, the command is 'show eigrp neighbors' (without 'ip') and output is more verbose. Between IOS versions (12.x, 15.x, 16.x), the command remains consistent, but newer versions may include additional fields like 'Auth' in detail output.
Always ensure you are in the correct VRF context when using the 'vrf' parameter. The command is available in all IOS privilege levels that have access to privileged EXEC mode (level 15).
Related Commands
show ip interface brief
Displays a one-line summary of all interfaces showing the IP address assigned, operational status (up/down), and line protocol status. The fastest way to get a device health overview.
show ip route
Displays the IP routing table showing all known routes, their source protocols, administrative distances, metrics, next-hops, and outgoing interfaces.
Practice for the CCNA 200-301
Test your knowledge with practice questions covering all CCNA 200-301 exam domains.
Practice CCNA 200-301 Questions