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EIGRPCCNA 200-301

EIGRP Route Stuck in Active State (SIA)

Presenting Symptom

An EIGRP route remains in active state for longer than expected, causing network instability and packet loss.

Network Context

A medium-sized enterprise network with multiple Cisco routers running IOS 15.x. EIGRP is used as the routing protocol in a hub-and-spoke topology with redundant links. The problem occurs when a link between two spoke routers fails, and the query/reply process for a specific route times out.

Diagnostic Steps

1

Check EIGRP topology table for stuck routes

show ip eigrp topology active
IP-EIGRP Topology Table for AS(100)/ID(10.0.0.1)
Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
       r - reply Status, s - sia Status

A 10.1.1.0/24, 1 successors, FD is 28160
    via 10.0.0.2 (28160/28160), Serial0/0/0
    via 10.0.0.3 (28672/28160), Serial0/0/1, s
    Reply count: 2, Reply peers: 2, Remaining replies: 1
    SIA sent: 0, SIA received: 0

The route is in Active state (A). The 's' flag on the next hop indicates that the route is stuck-in-active. The 'Remaining replies: 1' shows that one neighbor has not replied to the query.

2

Identify the non-responding neighbor

show ip eigrp neighbors
IP-EIGRP neighbors for process 100
H   Address                 Interface       Hold Uptime   SRTT   RTO  Q  Seq
                                           (sec)         (ms)       Cnt Num
0   10.0.0.2                Se0/0/0         13   00:12:34  1     200  0  45
1   10.0.0.3                Se0/0/1         14   00:12:35  2     200  0  46

Both neighbors are still listed, but the neighbor that is not replying may have a high SRTT or RTO, or may be unreachable. Check the interface status of the neighbor that is not replying.

3

Check interface status and connectivity to the non-responding neighbor

show ip interface brief | include Serial
Interface                  IP-Address      OK? Method Status                Protocol
Serial0/0/0                10.0.0.1        YES NVRAM  up                    up
Serial0/0/1                10.0.0.1        YES NVRAM  up                    up

If the interface is up/up, the issue may be a unidirectional link or a router that is not processing queries. If the interface is down, the neighbor is unreachable and the query will time out.

4

Check EIGRP SIA statistics and timers

show ip eigrp traffic
IP-EIGRP Traffic Statistics for AS 100
  Hellos sent/received: 1000/1000
  Updates sent/received: 50/50
  Queries sent/received: 10/8
  Replies sent/received: 8/10
  Acks sent/received: 60/60
  SIA-Queries sent/received: 2/0
  SIA-Replies sent/received: 0/0

SIA-Queries sent indicates that the router has sent SIA queries to neighbors to prevent the route from being stuck. If SIA-Queries are sent but no SIA-Replies received, the neighbor may be unresponsive.

Root Cause

A neighbor router is not replying to EIGRP queries within the active timer (default 3 minutes). This can be due to a unidirectional link, a router with high CPU load, or a router that is stuck in a query storm. In this case, the neighbor on Serial0/0/1 has a faulty interface causing intermittent packet loss, preventing reply packets from being sent back.

Resolution

Replace the faulty interface hardware or cable. If the issue is due to high CPU, reduce query scope by summarizing routes or adjusting timers. To clear the stuck route temporarily, use: clear ip eigrp neighbors 10.0.0.3 To adjust the active timer to a higher value (e.g., 5 minutes) to allow more time for replies: router eigrp 100 timers active-time 5 If the neighbor is unreachable, remove and re-add the neighbor or fix the underlying connectivity issue.

Verification

Run 'show ip eigrp topology active' again to confirm no routes are in Active state. Expected output: IP-EIGRP Topology Table for AS(100)/ID(10.0.0.1) Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, r - reply Status, s - sia Status P 10.1.1.0/24, 1 successors, FD is 28160 via 10.0.0.2 (28160/28160), Serial0/0/0 via 10.0.0.3 (28672/28160), Serial0/0/1 All routes should be Passive (P).

Prevention

1. Use EIGRP stub routing on spoke routers to limit query scope. 2. Summarize routes at distribution points to reduce the number of queries. 3. Ensure redundant links have proper load balancing and fast convergence mechanisms like EIGRP Fast Convergence features.

CCNA Exam Relevance

On the CCNA 200-301 exam, EIGRP SIA may appear in troubleshooting scenarios where a route is stuck in active. The exam tests understanding of the EIGRP query process, the meaning of the 's' flag, and commands like 'show ip eigrp topology active'. Candidates must know that SIA occurs when a neighbor does not reply within the active timer, and that clearing the neighbor or adjusting timers can resolve it.

Exam Tips

1.

Memorize the 'show ip eigrp topology active' command and the meaning of the 's' flag (stuck-in-active).

2.

Understand that SIA is caused by a neighbor not replying to a query within the active timer (default 3 minutes).

3.

Know that 'clear ip eigrp neighbors' can be used to reset the neighbor relationship and clear the SIA condition.

Commands Used in This Scenario

clear ip eigrp neighbors

This command immediately resets all EIGRP neighbor adjacencies, forcing the router to re-establish neighbor relationships and re-learn routes from all EIGRP neighbors.

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.

show ip eigrp traffic

Displays EIGRP packet statistics including sent/received counts for each packet type, used to verify EIGRP neighbor communication and troubleshoot packet loss or authentication issues.

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