debug ip eigrp summary
Use this command to display a summary of EIGRP neighbor adjacencies and route information, helping to quickly verify EIGRP operation and troubleshoot neighbor issues.
Definition: debug ip eigrp summary is a Cisco IOS privileged exec command. Use this command to display a summary of EIGRP neighbor adjacencies and route information, helping to quickly verify EIGRP operation and troubleshoot neighbor issues.
Overview
The 'debug ip eigrp summary' command is a powerful diagnostic tool used in Cisco's IOS to monitor Enhanced Interior Gateway Routing Protocol (EIGRP) operations at a high level. Unlike detailed EIGRP debugs that flood the console with every update, query, and reply, this command provides a concise summary of neighbor state changes, route table modifications, and key EIGRP events. It is particularly valuable for quickly verifying that EIGRP adjacencies are forming correctly and that routes are being exchanged without overwhelming the engineer with data.
The command operates in privileged EXEC mode (enable) and, like all debug commands, can significantly impact router performance if left running in a production environment. It does not alter the running configuration but generates real-time log messages that are displayed on the console or sent to a logging buffer. For CCNA and CCNP candidates, understanding when to use this command versus alternatives like 'show ip eigrp neighbors' or 'show ip eigrp topology' is crucial.
While show commands provide a static snapshot, debug commands reveal dynamic behavior, making them ideal for troubleshooting transient issues such as flapping neighbors or partial route loss. The summary variant is especially useful because it reduces noise; for example, instead of seeing every individual update packet, you see a line indicating that a neighbor has been added or removed, or that the route table has been updated. This command is often the first step in a structured EIGRP troubleshooting workflow: after verifying basic connectivity with ping, you enable 'debug ip eigrp summary' to watch neighbor formation and route exchange in real time.
If the summary indicates problems, you might escalate to more granular debugs like 'debug ip eigrp packets' or 'debug ip eigrp fsm'. Note that debug output is buffered by default; you can use 'terminal monitor' to see it on a remote session. The command requires privilege level 15 (enable mode).
It is safe to use in a lab but should be used sparingly in production due to CPU overhead. In summary, 'debug ip eigrp summary' is an essential tool for any network engineer working with EIGRP, providing a balance between visibility and performance impact.
debug ip eigrp summaryWhen to Use This Command
- After configuring EIGRP on a router, verify that neighbors have formed adjacencies and routes are being exchanged.
- When troubleshooting EIGRP neighbor flapping, check the summary to see neighbor status and uptime.
- During network maintenance, confirm that all expected EIGRP routes are present and that the router is learning routes from the correct neighbors.
- When investigating routing loops or suboptimal paths, review the summary to identify the number of routes and their sources.
Command Examples
Basic EIGRP Summary Output
debug ip eigrp summaryIP-EIGRP: Neighbor 10.1.1.2 (GigabitEthernet0/0) is up: new adjacency IP-EIGRP: Neighbor 10.1.1.2 (GigabitEthernet0/0) is up: adjacency IP-EIGRP: Received update from 10.1.1.2 (GigabitEthernet0/0) with 5 routes IP-EIGRP: Sending update to 10.1.1.2 (GigabitEthernet0/0) with 3 routes IP-EIGRP: Neighbor 192.168.1.2 (Serial0/0/0) is up: new adjacency IP-EIGRP: Neighbor 192.168.1.2 (Serial0/0/0) is up: adjacency IP-EIGRP: Received update from 192.168.1.2 (Serial0/0/0) with 8 routes IP-EIGRP: Sending update to 192.168.1.2 (Serial0/0/0) with 3 routes
The output shows EIGRP neighbor events and route exchanges. 'Neighbor ... is up: new adjacency' indicates a newly formed neighbor relationship. 'Received update from ... with X routes' shows the number of routes learned from that neighbor. 'Sending update to ... with X routes' shows the number of routes advertised to that neighbor. This helps verify that neighbors are forming and exchanging routes.
EIGRP Summary with Route Changes
debug ip eigrp summaryIP-EIGRP: Neighbor 10.1.1.2 (GigabitEthernet0/0) is up: adjacency IP-EIGRP: Received update from 10.1.1.2 (GigabitEthernet0/0) with 5 routes IP-EIGRP: Sending update to 10.1.1.2 (GigabitEthernet0/0) with 3 routes IP-EIGRP: Route 192.168.2.0/24 added to topology table IP-EIGRP: Route 192.168.3.0/24 deleted from topology table
This output shows normal neighbor adjacency and route updates. Additionally, it indicates specific route changes: 'Route ... added to topology table' means a new route was learned, while 'Route ... deleted from topology table' means a route was removed. This helps track dynamic routing changes.
Understanding the Output
The 'debug ip eigrp summary' command provides real-time information about EIGRP neighbor state changes and route updates. Each line begins with 'IP-EIGRP:' followed by the event. For neighbor events, you see the neighbor IP address, interface, and status (e.g., 'is up: new adjacency' for first-time adjacency, 'is up: adjacency' for stable adjacency).
For route updates, you see 'Received update from' with the neighbor and number of routes, and 'Sending update to' with the neighbor and number of routes. Additionally, individual route additions or deletions may appear as 'Route ... added to topology table' or 'Route ... deleted from topology table'. In a real network, you should see neighbor adjacencies form quickly after configuration.
If you see repeated 'new adjacency' messages, it indicates flapping. A high number of route changes may indicate instability. Use this debug to confirm that EIGRP is exchanging routes as expected.
Configuration Scenarios
Verifying EIGRP Neighbor Formation Between Two Routers
Two routers, R1 and R2, are connected via a serial link. EIGRP has been configured on both, but the neighbor adjacency is not forming. The engineer needs to watch the neighbor state machine in real time to identify the issue.
Topology
R1(Se0/0)---192.168.12.0/30---(Se0/0)R2Steps
- 1.Step 1: Enter privileged EXEC mode on R1: R1> enable
- 2.Step 2: Enable the debug: R1# debug ip eigrp summary
- 3.Step 3: Initiate a clear EIGRP neighbors to force re-formation: R1# clear ip eigrp neighbors
- 4.Step 4: Observe the debug output for neighbor state changes and any error messages.
- 5.Step 5: Disable debugging when done: R1# undebug all
! On R1: interface Serial0/0 ip address 192.168.12.1 255.255.255.252 ! router eigrp 100 network 192.168.12.0 0.0.0.3 ! ! On R2: interface Serial0/0 ip address 192.168.12.2 255.255.255.252 ! router eigrp 100 network 192.168.12.0 0.0.0.3
Verify: Expected debug output shows: 'EIGRP: New neighbor 192.168.12.2, interface Serial0/0' followed by 'EIGRP: Neighbor 192.168.12.2 went from Loading to Full'. If adjacency fails, you may see 'EIGRP: Neighbor 192.168.12.2 went from Init to Down' or 'EIGRP: Retransmission limit exceeded'.
Watch out: A common mistake is forgetting to use 'terminal monitor' when connected via Telnet/SSH; otherwise, debug output is not displayed on the remote session.
Monitoring Route Injection and Removal in an EIGRP Network
A new subnet is being added to an existing EIGRP domain. The engineer wants to confirm that the route is being advertised and received by all neighbors without flooding the console with detailed packet debugs.
Topology
R1(Gi0/0)---10.0.12.0/30---(Gi0/0)R2---(Gi0/1)---10.0.23.0/30---(Gi0/0)R3
R3 has a loopback 172.16.1.0/24 to be advertised.Steps
- 1.Step 1: On R2, enable the debug: R2# debug ip eigrp summary
- 2.Step 2: On R3, configure the loopback and advertise it under EIGRP.
- 3.Step 3: Observe R2's debug output for route addition.
- 4.Step 4: Verify with 'show ip route eigrp' that the route appears.
- 5.Step 5: Disable debugging: R2# undebug all
! On R3: interface Loopback0 ip address 172.16.1.1 255.255.255.0 ! router eigrp 100 network 172.16.1.0 0.0.0.255
Verify: Expected debug output on R2: 'EIGRP: Route added to table: 172.16.1.0/24 via 10.0.23.2, Serial0/1'. If the route is not added, you may see 'EIGRP: Route 172.16.1.0/24 not installed because it is a duplicate' or no output at all, indicating a reachability or configuration issue.
Watch out: If the route is already in the topology table but not in the routing table, the debug may not show an 'added' message. Use 'show ip eigrp topology' to check if the route is present but stuck in active state.
Troubleshooting with This Command
When troubleshooting EIGRP issues, 'debug ip eigrp summary' is your first line of defense. Healthy output typically shows neighbor state transitions from Init to Loading to Full, and route additions or removals are logged concisely. For example, a normal adjacency formation will produce: 'EIGRP: New neighbor 10.0.12.2, interface GigabitEthernet0/0' followed by 'EIGRP: Neighbor 10.0.12.2 went from Loading to Full'.
Route changes appear as 'EIGRP: Route added to table: 192.168.1.0/24 via 10.0.12.2, GigabitEthernet0/0'. Problem indicators include repeated neighbor state changes (flapping), such as 'EIGRP: Neighbor 10.0.12.2 went from Full to Down' followed by re-initiation. This often points to Layer 1/2 issues, mismatched K-values, or authentication failures.
Another common symptom is the absence of any neighbor output when you expect adjacency; this suggests a configuration mismatch (e.g., different AS numbers, passive interface, or network statement missing). The debug also helps diagnose stuck-in-active (SIA) routes: if you see 'EIGRP: Route 10.0.0.0/8 is stuck in active' or repeated queries for the same route, it indicates a neighbor is not replying to queries, possibly due to a unidirectional link or high CPU. A step-by-step diagnostic flow: 1) Enable 'debug ip eigrp summary' and clear neighbors with 'clear ip eigrp neighbors'. 2) Watch for neighbor state changes.
If no neighbors appear, check 'show ip eigrp interfaces' to verify EIGRP is enabled on the correct interfaces. 3) If neighbors form but routes are missing, look for 'Route added' messages. If a route is not added, check 'show ip eigrp topology' to see if the route is in the topology table but not installed (e.g., due to administrative distance or metric). 4) If you see 'Retransmission limit exceeded' or 'Hold time expired', suspect packet loss or mismatched timers. Correlate with 'show ip eigrp neighbors' to see uptime and retransmission counts.
Also use 'show ip eigrp traffic' to see if packets are being sent/received. Remember that debug output is high priority and can cause CPU spikes; always use 'undebug all' when done. In production, consider using conditional debugging with 'debug ip eigrp summary | include <neighbor-ip>' to filter output.
This command is invaluable for isolating EIGRP issues quickly without the noise of full packet debugging.
CCNA Exam Tips
CCNA exam tip: The 'debug ip eigrp summary' command is useful for verifying neighbor formation and route exchange, but remember that debug commands are CPU-intensive and should be used with caution in production.
CCNA exam tip: In the exam, you may be asked to interpret debug output to determine if EIGRP neighbors are forming correctly. Look for 'is up: adjacency' to confirm stable neighbors.
CCNA exam tip: Know that 'debug ip eigrp summary' shows only summary information; for detailed route information, use 'show ip eigrp topology'.
CCNA exam tip: Be aware that 'undebug all' or 'no debug ip eigrp summary' is used to disable debugging to avoid excessive CPU load.
Common Mistakes
Mistake 1: Leaving debug enabled after troubleshooting, which can cause high CPU usage and impact router performance. Always disable debug with 'undebug all' or 'no debug ip eigrp summary'.
Mistake 2: Confusing 'debug ip eigrp summary' with 'show ip eigrp summary'. The debug command shows real-time events, while the show command displays a static summary.
Mistake 3: Expecting to see route details in the summary debug output. This command only shows neighbor events and route counts, not specific route entries.
debug ip eigrp summary vs debug ip eigrp
Both 'debug ip eigrp summary' and 'debug ip eigrp' are troubleshooting commands for EIGRP, but they serve different purposes. The summary variant provides high-level neighbor and route information, while the standard command outputs detailed packet-level events, often causing high CPU load. They are commonly confused because of similar naming, but their verbosity and impact differ significantly.
| Aspect | debug ip eigrp summary | debug ip eigrp |
|---|---|---|
| Scope | Neighbor adjacencies and route summary only | All EIGRP packets and events |
| Verbosity | Low - outputs brief, summarized lines | High - outputs each packet, update, query, reply |
| Output detail | Shows neighbor state changes, routes, timers | Shows packet headers, sequence numbers, metrics |
| CPU impact | Minimal - suitable for production with caution | High - can cause router crash in production |
| Typical use | Quick verification of EIGRP health | Deep troubleshooting of specific issues |
Use debug ip eigrp summary when you need a quick overview of EIGRP neighbor and route status without overwhelming the router with packet-level details.
Use debug ip eigrp when you must analyze every EIGRP packet exchange to diagnose complex neighbor or route exchange problems, but only during maintenance windows or lab environments.
Platform Notes
In IOS-XE (e.g., Catalyst 9000 switches, ISR 4000 series), the 'debug ip eigrp summary' command syntax and output are identical to classic IOS. However, IOS-XE may have additional logging capabilities, such as sending debug output to a syslog server with different severity levels. The command is also available in IOS-XR, but the syntax differs: use 'debug eigrp summary' (without 'ip') in XR.
For example, in IOS-XR: 'debug eigrp summary' provides similar neighbor and route summary information. Note that IOS-XR uses a different process architecture, so the output may include process IDs. On NX-OS (Cisco Nexus switches), the equivalent command is 'debug eigrp summary' as well, but NX-OS uses a modular design; you may need to enable the EIGRP feature first with 'feature eigrp'.
The output format is similar but may include VRF information. For ASA firewalls, EIGRP is not supported in classic ASA code; however, in ASA with FirePOWER services, EIGRP may be available in the routed mode, but debugging is done via the underlying IOS-like environment. In general, for IOS versions 12.x, 15.x, and 16.x, the command behavior is consistent.
One difference: in older IOS (12.x), the debug output might be more verbose, including timestamps by default, while newer versions may require 'service timestamps debug' to enable timestamps. Always check the specific platform documentation, but the command remains a reliable tool across Cisco platforms for EIGRP summary debugging.
Related Commands
debug ip eigrp
This command enables real-time debugging of EIGRP packets and events on a Cisco router, used to troubleshoot EIGRP neighbor relationships, route exchanges, and metric calculations.
show ip eigrp neighbors
Displays all EIGRP neighbours with their addresses, interfaces, hold time, uptime, SRTT (smooth round-trip time), RTO, queue count, and sequence numbers.
show ip eigrp topology
Displays the EIGRP topology table, showing all learned routes and their feasible successors, used to verify EIGRP convergence and path selection.
undebug all
Disables all active debug operations on the router, used to stop debugging output and reduce CPU load.
Practice for the CCNA 200-301
Test your knowledge with practice questions covering all CCNA 200-301 exam domains.
Practice CCNA 200-301 Questions