Courseiva
EIGRPCCNA 200-301

EIGRP Hold Timer Expired — Neighbor Keeps Dropping

Presenting Symptom

EIGRP neighbor flapping every 15-20 seconds with 'Hold timer expired' error messages.

Network Context

A small branch office with two Cisco routers (R1 and R2) connected via a serial link (T1). Both run IOS 15.x. The EIGRP AS is 100. The link is stable but EIGRP neighbors keep dropping and re-establishing.

Diagnostic Steps

1

Check EIGRP neighbor status

show ip eigrp neighbors
EIGRP-IPv4 Neighbors for AS(100)
H   Address                 Interface       Hold Uptime   SRTT   RTO  Q  Seq
                                        (sec) (h:m:s)   (ms)       Cnt Num
0   192.168.1.2             Serial0/0/0     13 00:00:15   1     200  0  1

Look for the Hold column. Normal hold time is 15 seconds. If it shows a value less than 15 (e.g., 13) and the uptime is low, the neighbor is flapping. The Q count should be 0; non-zero indicates issues.

2

Verify EIGRP timers on both routers

show ip eigrp interfaces detail Serial0/0/0
EIGRP-IPv4 Interfaces for AS(100)
                       Xmit Queue   Mean   Pacing Time   Multicast    Pending
Interface        Peers  Un/Reliable  SRTT   Un/Reliable   Flow Timer   Routes
Se0/0/0            1       0/0       1       0/10         50           0
  Hello interval: 5 sec, Hold time: 15 sec

Check the Hello interval and Hold time. They should match on both ends. If one router has different timers (e.g., Hello 10, Hold 30), the neighbor will drop when the hold timer expires.

3

Check for interface errors or flapping

show interfaces Serial0/0/0
Serial0/0/0 is up, line protocol is up
  Hardware is HD64570
  Internet address is 192.168.1.1/30
  MTU 1500 bytes, BW 1544 Kbit/sec, DLY 20000 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation HDLC, loopback not set
  Keepalive set (10 sec)
  ...
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     0 packets input, 0 bytes, 0 no buffer
     Received 0 broadcasts (0 IP multicasts)
     0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
     0 watchdog, 0 multicast, 0 pause input
     0 input packets with dribble condition detected
     0 packets output, 0 bytes, 0 underruns
     0 output errors, 0 collisions, 0 interface resets
     0 unknown protocol drops
     0 babbles, 0 late collision, 0 deferred
     0 lost carrier, 0 no carrier, 0 pause output
     0 output buffer failures, 0 output buffers swapped out

Look for input errors, output errors, interface resets, or carrier transitions. If errors are high, the physical layer may be causing packet loss, leading to hold timer expiry.

4

Enable EIGRP debug to see hello packet exchange

debug eigrp packets hello
EIGRP: Received HELLO on Serial0/0/0 nbr 192.168.1.2
  AS 100, Flags 0x0, Seq 0/0 interfaceQ 0/0
EIGRP: Sending HELLO on Serial0/0/0
  AS 100, Flags 0x0, Seq 0/0 interfaceQ 0/0

If you see 'Received HELLO' but then the neighbor drops, the hold timer may be too short. If you see no HELLO packets, the link is down or misconfigured. If you see 'K value mismatch' or 'Authentication mismatch', that's the root cause.

Root Cause

The EIGRP hello and hold timers are mismatched between the two routers. R1 has default timers (hello 5 sec, hold 15 sec) while R2 has been configured with non-default timers (hello 10 sec, hold 30 sec). When R1 sends a hello every 5 seconds, R2 expects it every 10 seconds, so it's fine. But R2 sends a hello every 10 seconds, and R1's hold timer is 15 seconds. If a hello is delayed or lost, R1's hold timer expires after 15 seconds, causing the neighbor to drop. The neighbor re-establishes when the next hello arrives.

Resolution

On R2, configure the EIGRP timers to match R1's defaults: R2(config)# interface Serial0/0/0 R2(config-if)# ip hello-interval eigrp 100 5 R2(config-if)# ip hold-time eigrp 100 15 This sets the hello interval to 5 seconds and hold time to 15 seconds for EIGRP AS 100 on that interface.

Verification

Run 'show ip eigrp neighbors' on both routers. The Hold column should show 15 (or close to it) and the uptime should be increasing. Run 'show ip eigrp interfaces detail Serial0/0/0' to confirm timers: Hello interval: 5 sec, Hold time: 15 sec. The neighbor should remain stable.

Prevention

1. Use consistent EIGRP timer configurations across all routers in the same AS. 2. Avoid changing default timers unless necessary for convergence tuning. 3. Document any non-default timer settings and ensure they match on all neighbors.

CCNA Exam Relevance

On the CCNA 200-301 exam, this scenario may appear as a troubleshooting question where you must identify why an EIGRP neighbor is flapping. The exam tests your ability to interpret 'show ip eigrp neighbors' and 'show ip eigrp interfaces detail' output. Key fact: EIGRP hello and hold timers must match for neighbor adjacency to stay up; the hold timer must be at least three times the hello interval.

Exam Tips

1.

Remember that EIGRP hello and hold timers are configured per interface and must match on both ends.

2.

The default hello interval is 5 seconds (60 seconds for NBMA) and hold time is 15 seconds (180 seconds for NBMA).

3.

Use 'show ip eigrp interfaces detail' to quickly verify timer values.

Commands Used in This Scenario

show ip eigrp neighbors

Displays the neighbor table for EIGRP, showing all directly connected EIGRP routers and their status, used to verify EIGRP adjacencies and troubleshoot neighbor relationships.

Test Your CCNA Knowledge

Practice with scenario-based questions to prepare for the CCNA 200-301 exam.

Practice CCNA Questions