CCNP Lab 12.3 - EIGRP Stuck in Active - Iconic InfoSec Training

🔧 Lab 12.3: EIGRP Stuck in Active (SIA) - Troubleshooting & Prevention

Cisco CCNP 350-401 (ENCOR) & 300-410 (ENARSI) - Advanced EIGRP Troubleshooting

📚 Lab Overview
Duration: 120-150 minutes | Difficulty Level: Advanced | Lab Version: 1.0
Lab ID: Lab 12.3 | Topics: EIGRP Stuck in Active, Query Propagation, SIA Prevention
Autonomous System: AS 100 | Focus: DUAL Algorithm, Query Scoping, Stub Routing

🎯 Lab Objectives

Upon completion of this lab, you will be able to:

✓ Understand EIGRP Stuck in Active (SIA) condition and its causes
✓ Configure EIGRP on a complex 6-router topology
✓ Simulate and observe SIA conditions in EIGRP networks
✓ Implement EIGRP stub routing to prevent query propagation
✓ Configure route summarization to limit query scope
✓ Monitor and troubleshoot SIA-related issues
✓ Implement Active Timer adjustments for SIA prevention
✓ Use EIGRP event logging to track SIA occurrences
✓ Apply best practices for preventing SIA in production networks
✓ Analyze EIGRP topology states (Passive, Active, SIA-Query, SIA-Reply)

📊 Network Topology

Figure 1: EIGRP SIA Troubleshooting Topology (6 Routers)

ℹ️ Topology Description:
This lab features a complex 6-router EIGRP topology designed to demonstrate and troubleshoot Stuck in Active (SIA) conditions. R1 acts as the core router with connections to R2, R3, and R4. R6 serves as a convergence point receiving routes from multiple paths through R2, R3, and R5. This topology is ideal for observing query propagation and implementing SIA prevention techniques.

🖥️ Device Information

Device Name	Device Type	EIGRP AS	Role	IOS Version
R1	Cisco Router	AS 100	Core Router / Query Source	IOS 15.x or higher
R2	Cisco Router	AS 100	Distribution Router	IOS 15.x or higher
R3	Cisco Router	AS 100	Distribution Router	IOS 15.x or higher
R4	Cisco Router	AS 100	Distribution Router	IOS 15.x or higher
R5	Cisco Router	AS 100	Edge Router / Stub Candidate	IOS 15.x or higher
R6	Cisco Router	AS 100	Convergence Point / Edge Router	IOS 15.x or higher

📋 IP Addressing Table

Device	Interface	IP Address	Subnet Mask	Network
R1	GigabitEthernet0/0	203.18.61.1	255.255.255.252 (/30)	203.18.61.0/30
R1	GigabitEthernet0/1	203.18.61.5	255.255.255.252 (/30)	203.18.61.4/30
R1	GigabitEthernet1/0	203.18.61.9	255.255.255.252 (/30)	203.18.61.8/30
R1	Loopback0	192.168.1.1	255.255.255.0 (/24)	192.168.1.0/24
R2	GigabitEthernet0/0	203.18.61.2	255.255.255.252 (/30)	203.18.61.0/30
R2	GigabitEthernet1/0	203.18.62.1	255.255.255.252 (/30)	203.18.62.0/30
R2	Loopback0	192.168.2.1	255.255.255.0 (/24)	192.168.2.0/24
R3	GigabitEthernet0/1	203.18.61.6	255.255.255.252 (/30)	203.18.61.4/30
R3	GigabitEthernet1/1	203.18.63.1	255.255.255.252 (/30)	203.18.63.0/30
R3	Loopback0	192.168.3.1	255.255.255.0 (/24)	192.168.3.0/24
R4	GigabitEthernet1/0	203.18.61.10	255.255.255.252 (/30)	203.18.61.8/30
R4	GigabitEthernet0/0	203.18.64.1	255.255.255.252 (/30)	203.18.64.0/30
R4	Loopback0	192.168.4.1	255.255.255.0 (/24)	192.168.4.0/24
R5	GigabitEthernet0/0	203.18.64.2	255.255.255.252 (/30)	203.18.64.0/30
R5	GigabitEthernet0/1	203.18.65.1	255.255.255.252 (/30)	203.18.65.0/30
R5	Loopback0	192.168.5.1	255.255.255.0 (/24)	192.168.5.0/24
R6	GigabitEthernet1/0	203.18.62.2	255.255.255.252 (/30)	203.18.62.0/30
R6	GigabitEthernet1/1	203.18.63.2	255.255.255.252 (/30)	203.18.63.0/30
R6	GigabitEthernet0/1	203.18.65.2	255.255.255.252 (/30)	203.18.65.0/30
R6	Loopback0	192.168.6.1	255.255.255.0 (/24)	192.168.6.0/24

🔌 Cable Connection Information

Connection	Device 1	Interface 1	Device 2	Interface 2	Network
Link 1	R1	G0/0	R2	G0/0	203.18.61.0/30
Link 2	R1	G0/1	R3	G0/1	203.18.61.4/30
Link 3	R1	G1/0	R4	G1/0	203.18.61.8/30
Link 4	R2	G1/0	R6	G1/0	203.18.62.0/30
Link 5	R3	G1/1	R6	G1/1	203.18.63.0/30
Link 6	R4	G0/0	R5	G0/0	203.18.64.0/30
Link 7	R5	G0/1	R6	G0/1	203.18.65.0/30

📚 Prerequisites

⚠️ Before You Begin:
• Completion of Lab 12.1 and Lab 12.2 strongly recommended
• Deep understanding of EIGRP DUAL algorithm and FSM
• Knowledge of EIGRP query and reply mechanisms
• Understanding of Feasible Distance (FD) and Reported Distance (RD)
• Familiarity with EIGRP topology states (Passive, Active)
• Experience with EIGRP route summarization and stub routing
• Advanced Cisco IOS CLI troubleshooting skills
• Understanding of network convergence concepts

📖 Understanding EIGRP Stuck in Active (SIA)

🚨 What is Stuck in Active (SIA)?

Definition: SIA occurs when a router sends EIGRP queries about a route but does not receive replies from all neighbors within the Active Timer period (default 3 minutes / 180 seconds).

Consequences:
• Neighbor relationships are reset with routers that didn't reply
• Routing instability and convergence issues
• Potential network outages
• CPU and memory resource consumption

Root Causes:
• Slow WAN links delaying query/reply propagation
• Routing loops causing queries to circulate
• Large network diameter with many hops
• Congested links dropping EIGRP packets
• Misconfigured or missing route summarization
• Router resource exhaustion (CPU/memory)
• Lack of stub routing implementation

📘 EIGRP Query Mechanism:

Normal Operation:
1. Route goes down (successor lost)
2. Router checks for Feasible Successor (FS)
3. If FS exists: Immediate convergence (route in Passive state)
4. If NO FS: Router enters Active state and sends Queries
5. Queries propagate to all neighbors (except route source)
6. Each neighbor must Reply to the Query
7. Once all Replies received: Route returns to Passive state

SIA Condition:
• If any neighbor fails to Reply within 180 seconds → SIA
• Router resets neighbor relationship with non-responding router
• Can trigger cascading SIA across network

⚙️ Step-by-Step Configuration Guide

📝 Step 1: Basic Interface Configuration on All Routers

Task 1.1: Configure R1 Interfaces (Core Router)

R1> enable

R1# configure terminal

R1(config)# hostname R1

! Configure G0/0 (to R2)

R1(config)# interface gigabitethernet 0/0

R1(config-if)# description ** Link to R2 **

R1(config-if)# ip address 203.18.61.1 255.255.255.252

R1(config-if)# no shutdown

R1(config-if)# exit

! Configure G0/1 (to R3)

R1(config)# interface gigabitethernet 0/1

R1(config-if)# description ** Link to R3 **

R1(config-if)# ip address 203.18.61.5 255.255.255.252

R1(config-if)# no shutdown

R1(config-if)# exit

! Configure G1/0 (to R4)

R1(config)# interface gigabitethernet 1/0

R1(config-if)# description ** Link to R4 **

R1(config-if)# ip address 203.18.61.9 255.255.255.252

R1(config-if)# no shutdown

R1(config-if)# exit

! Configure Loopback0

R1(config)# interface loopback 0

R1(config-if)# description ** R1 Internal Network **

R1(config-if)# ip address 192.168.1.1 255.255.255.0

R1(config-if)# exit

R1(config)# end

R1# write memory

Task 1.2: Configure R2 Interfaces

R2# configure terminal

R2(config)# hostname R2

! Configure G0/0 (to R1)

R2(config)# interface gigabitethernet 0/0

R2(config-if)# description ** Link to R1 **

R2(config-if)# ip address 203.18.61.2 255.255.255.252

R2(config-if)# no shutdown

R2(config-if)# exit

! Configure G1/0 (to R6)

R2(config)# interface gigabitethernet 1/0

R2(config-if)# description ** Link to R6 **

R2(config-if)# ip address 203.18.62.1 255.255.255.252

R2(config-if)# no shutdown

R2(config-if)# exit

! Configure Loopback0

R2(config)# interface loopback 0

R2(config-if)# description ** R2 Internal Network **

R2(config-if)# ip address 192.168.2.1 255.255.255.0

R2(config-if)# exit

R2(config)# end

R2# write memory

Task 1.3: Configure R3 Interfaces

R3# configure terminal

R3(config)# hostname R3

! Configure G0/1 (to R1)

R3(config)# interface gigabitethernet 0/1

R3(config-if)# description ** Link to R1 **

R3(config-if)# ip address 203.18.61.6 255.255.255.252

R3(config-if)# no shutdown

R3(config-if)# exit

! Configure G1/1 (to R6)

R3(config)# interface gigabitethernet 1/1

R3(config-if)# description ** Link to R6 **

R3(config-if)# ip address 203.18.63.1 255.255.255.252

R3(config-if)# no shutdown

R3(config-if)# exit

! Configure Loopback0

R3(config)# interface loopback 0

R3(config-if)# description ** R3 Internal Network **

R3(config-if)# ip address 192.168.3.1 255.255.255.0

R3(config-if)# exit

R3(config)# end

R3# write memory

Task 1.4: Configure R4 Interfaces

R4# configure terminal

R4(config)# hostname R4

! Configure G1/0 (to R1)

R4(config)# interface gigabitethernet 1/0

R4(config-if)# description ** Link to R1 **

R4(config-if)# ip address 203.18.61.10 255.255.255.252

R4(config-if)# no shutdown

R4(config-if)# exit

! Configure G0/0 (to R5)

R4(config)# interface gigabitethernet 0/0

R4(config-if)# description ** Link to R5 **

R4(config-if)# ip address 203.18.64.1 255.255.255.252

R4(config-if)# no shutdown

R4(config-if)# exit

! Configure Loopback0

R4(config)# interface loopback 0

R4(config-if)# description ** R4 Internal Network **

R4(config-if)# ip address 192.168.4.1 255.255.255.0

R4(config-if)# exit

R4(config)# end

R4# write memory

Task 1.5: Configure R5 Interfaces

R5# configure terminal

R5(config)# hostname R5

! Configure G0/0 (to R4)

R5(config)# interface gigabitethernet 0/0

R5(config-if)# description ** Link to R4 **

R5(config-if)# ip address 203.18.64.2 255.255.255.252

R5(config-if)# no shutdown

R5(config-if)# exit

! Configure G0/1 (to R6)

R5(config)# interface gigabitethernet 0/1

R5(config-if)# description ** Link to R6 **

R5(config-if)# ip address 203.18.65.1 255.255.255.252

R5(config-if)# no shutdown

R5(config-if)# exit

! Configure Loopback0

R5(config)# interface loopback 0

R5(config-if)# description ** R5 Internal Network **

R5(config-if)# ip address 192.168.5.1 255.255.255.0

R5(config-if)# exit

R5(config)# end

R5# write memory

Task 1.6: Configure R6 Interfaces (Convergence Point)

R6# configure terminal

R6(config)# hostname R6

! Configure G1/0 (to R2)

R6(config)# interface gigabitethernet 1/0

R6(config-if)# description ** Link to R2 **

R6(config-if)# ip address 203.18.62.2 255.255.255.252

R6(config-if)# no shutdown

R6(config-if)# exit

! Configure G1/1 (to R3)

R6(config)# interface gigabitethernet 1/1

R6(config-if)# description ** Link to R3 **

R6(config-if)# ip address 203.18.63.2 255.255.255.252

R6(config-if)# no shutdown

R6(config-if)# exit

! Configure G0/1 (to R5)

R6(config)# interface gigabitethernet 0/1

R6(config-if)# description ** Link to R5 **

R6(config-if)# ip address 203.18.65.2 255.255.255.252

R6(config-if)# no shutdown

R6(config-if)# exit

! Configure Loopback0

R6(config)# interface loopback 0

R6(config-if)# description ** R6 Internal Network **

R6(config-if)# ip address 192.168.6.1 255.255.255.0

R6(config-if)# exit

R6(config)# end

R6# write memory

Task 1.7: Verify Interface Configuration

! Verify on each router

R1# show ip interface brief

R2# show ip interface brief

R3# show ip interface brief

R4# show ip interface brief

R5# show ip interface brief

R6# show ip interface brief

! Test connectivity between directly connected routers

R1# ping 203.18.61.2

R1# ping 203.18.61.6

R1# ping 203.18.61.10

✅ Checkpoint 1: All interfaces configured and in "up/up" state. Basic IP connectivity verified between directly connected routers.

📝 Step 2: Basic EIGRP Configuration (AS 100)

Task 2.1: Configure EIGRP on R1

R1# configure terminal

R1(config)# router eigrp 100

R1(config-router)# network 203.18.61.0 0.0.0.3

R1(config-router)# network 203.18.61.4 0.0.0.3

R1(config-router)# network 203.18.61.8 0.0.0.3

R1(config-router)# network 192.168.1.0 0.0.0.255

R1(config-router)# no auto-summary

R1(config-router)# eigrp router-id 1.1.1.1

R1(config-router)# exit

R1(config)# end

R1# write memory

Task 2.2: Configure EIGRP on R2

R2# configure terminal

R2(config)# router eigrp 100

R2(config-router)# network 203.18.61.0 0.0.0.3

R2(config-router)# network 203.18.62.0 0.0.0.3

R2(config-router)# network 192.168.2.0 0.0.0.255

R2(config-router)# no auto-summary

R2(config-router)# eigrp router-id 2.2.2.2

R2(config-router)# exit

R2(config)# end

R2# write memory

Task 2.3: Configure EIGRP on R3

R3# configure terminal

R3(config)# router eigrp 100

R3(config-router)# network 203.18.61.4 0.0.0.3

R3(config-router)# network 203.18.63.0 0.0.0.3

R3(config-router)# network 192.168.3.0 0.0.0.255

R3(config-router)# no auto-summary

R3(config-router)# eigrp router-id 3.3.3.3

R3(config-router)# exit

R3(config)# end

R3# write memory

Task 2.4: Configure EIGRP on R4

R4# configure terminal

R4(config)# router eigrp 100

R4(config-router)# network 203.18.61.8 0.0.0.3

R4(config-router)# network 203.18.64.0 0.0.0.3

R4(config-router)# network 192.168.4.0 0.0.0.255

R4(config-router)# no auto-summary

R4(config-router)# eigrp router-id 4.4.4.4

R4(config-router)# exit

R4(config)# end

R4# write memory

Task 2.5: Configure EIGRP on R5

R5# configure terminal

R5(config)# router eigrp 100

R5(config-router)# network 203.18.64.0 0.0.0.3

R5(config-router)# network 203.18.65.0 0.0.0.3

R5(config-router)# network 192.168.5.0 0.0.0.255

R5(config-router)# no auto-summary

R5(config-router)# eigrp router-id 5.5.5.5

R5(config-router)# exit

R5(config)# end

R5# write memory

Task 2.6: Configure EIGRP on R6

R6# configure terminal

R6(config)# router eigrp 100

R6(config-router)# network 203.18.62.0 0.0.0.3

R6(config-router)# network 203.18.63.0 0.0.0.3

R6(config-router)# network 203.18.65.0 0.0.0.3

R6(config-router)# network 192.168.6.0 0.0.0.255

R6(config-router)# no auto-summary

R6(config-router)# eigrp router-id 6.6.6.6

R6(config-router)# exit

R6(config)# end

R6# write memory

Task 2.7: Verify EIGRP Neighbor Relationships

! Check neighbors on all routers

R1# show ip eigrp neighbors

! Should see R2, R3, R4

R2# show ip eigrp neighbors

! Should see R1, R6

R3# show ip eigrp neighbors

! Should see R1, R6

R4# show ip eigrp neighbors

! Should see R1, R5

R5# show ip eigrp neighbors

! Should see R4, R6

R6# show ip eigrp neighbors

! Should see R2, R3, R5

Task 2.8: Verify EIGRP Routing Tables

! Check routing tables

R1# show ip route eigrp

! Should see routes to all loopbacks

R6# show ip route eigrp

! Should see routes to all loopbacks including R1's

! Test end-to-end connectivity

R1# ping 192.168.6.1 source 192.168.1.1

R6# ping 192.168.1.1 source 192.168.6.1

✅ Checkpoint 2: EIGRP neighbors established on all routers. Full routing table convergence achieved. End-to-end connectivity verified.

📝 Step 3: Enable EIGRP Event Logging for SIA Monitoring

Task 3.1: Enable EIGRP Event Logging on All Routers

! On R1

R1# configure terminal

R1(config)# router eigrp 100

R1(config-router)# eigrp event-log-size 100000

R1(config-router)# eigrp log-neighbor-changes

R1(config-router)# eigrp log-neighbor-warnings

R1(config-router)# exit

R1(config)# end

! Repeat on R2, R3, R4, R5, R6

! (Use same commands on each router)

📘 Event Logging Commands Explained:
• eigrp event-log-size 100000: Stores up to 100,000 EIGRP events
• eigrp log-neighbor-changes: Logs neighbor up/down events
• eigrp log-neighbor-warnings: Logs SIA and other warnings

These logs are critical for identifying SIA occurrences and troubleshooting!

Task 3.2: Verify Event Logging Configuration

R1# show ip protocols | include Event

! Output: Event-log enabled, Maximum size: 100000

R1# show eigrp address-family ipv4 events

! Shows EIGRP event log (currently should be mostly neighbor events)

📝 Step 4: Simulate and Observe SIA Condition

⚠️ WARNING - CONTROLLED SIA SIMULATION:
The following steps will intentionally create a Stuck in Active condition for educational purposes. This will cause temporary routing instability. In production networks, NEVER intentionally create SIA conditions.

Task 4.1: Prepare for SIA Simulation

! On R1, enable debugging (use with caution)

R1# debug eigrp fsm

R1# debug eigrp packets query

R1# debug eigrp packets reply

! Monitor EIGRP topology

R1# show ip eigrp topology 192.168.6.0/24

! Note the current state (should be Passive)

Task 4.2: Create SIA Condition by Delaying Replies

Method 1: Temporarily Block EIGRP Communication on R6

! On R6, create an access-list to block EIGRP (Protocol 88)

R6# configure terminal

R6(config)# access-list 100 deny eigrp any any

R6(config)# access-list 100 permit ip any any

! Apply to interfaces (temporarily)

R6(config)# interface gigabitethernet 1/0

R6(config-if)# ip access-group 100 in

R6(config-if)# exit

R6(config)# interface gigabitethernet 1/1

R6(config-if)# ip access-group 100 in

R6(config-if)# exit

R6(config)# end

Task 4.3: Trigger Active State on R1

! On R5, shut down loopback to trigger query from R1

R5# configure terminal

R5(config)# interface loopback 0

R5(config-if)# shutdown

R5(config-if)# end

! R1 will send queries for 192.168.5.0/24

! Watch debug output on R1

Task 4.4: Observe SIA Behavior

! On R1, monitor topology state

R1# show ip eigrp topology active

! Will show routes in Active state

! Check EIGRP events

R1# show eigrp address-family ipv4 events | include SIA

! After 90 seconds, EIGRP sends SIA-Query

! After 180 seconds total, SIA condition declared

! Watch for neighbor reset messages:

! %DUAL-5-NBRCHANGE: EIGRP-IPv4 100: Neighbor X.X.X.X (interface) 

! is down: stuck in active

Task 4.5: Restore Normal Operation

! Remove ACL on R6

R6# configure terminal

R6(config)# interface gigabitethernet 1/0

R6(config-if)# no ip access-group 100 in

R6(config-if)# exit

R6(config)# interface gigabitethernet 1/1

R6(config-if)# no ip access-group 100 in

R6(config-if)# exit

R6(config)# no access-list 100

R6(config)# end

! Bring R5 loopback back up

R5# configure terminal

R5(config)# interface loopback 0

R5(config-if)# no shutdown

R5(config-if)# end

! Disable debugs on R1

R1# undebug all

! Allow EIGRP to reconverge (may take 1-2 minutes)

Task 4.6: Analyze SIA Event Log

! View complete event log

R1# show eigrp address-family ipv4 events | include SIA

! Example output:

! 00:15:23.456 SIA-QUERY sent for 192.168.5.0/24

! 00:18:23.789 SIA declared for 192.168.5.0/24

! 00:18:23.790 Neighbor 203.18.61.2 reset: stuck in active

! Check EIGRP traffic statistics

R1# show ip eigrp traffic

! Look for SIA-Queries and SIA-Replies counts

✅ Checkpoint 3: SIA condition successfully simulated and observed. Event logs captured SIA occurrence. Normal operation restored.

📝 Step 5: Implement SIA Prevention - EIGRP Stub Routing

EIGRP stub routing prevents query propagation to stub routers, significantly reducing the query domain and preventing SIA.

Task 5.1: Configure R5 as EIGRP Stub Router

R5# configure terminal

R5(config)# router eigrp 100

R5(config-router)# eigrp stub connected

R5(config-router)# exit

R5(config)# end

R5# write memory

📘 EIGRP Stub Options:
• eigrp stub connected: Advertise only connected routes
• eigrp stub summary: Advertise only summary routes
• eigrp stub static: Advertise only static routes
• eigrp stub redistributed: Advertise only redistributed routes
• eigrp stub receive-only: Don't advertise any routes
• eigrp stub: Default = connected + summary

Stub routers do NOT receive queries, preventing SIA propagation!

Task 5.2: Verify Stub Configuration

! On R5, verify stub configuration

R5# show ip protocols | include Stub

! Output: Routing Protocol is "eigrp 100"

!         Stub, connected

! On R4 (neighbor of R5), verify stub status

R4# show ip eigrp neighbors detail

! Look for "Stub Peer Advertising ( CONNECTED )" in output

! Example output:

! H   Address         Interface     Hold Uptime   SRTT   RTO  Q  Seq

!                                   (sec)         (ms)       Cnt Num

! 1   203.18.64.2     Gi0/0          14 00:05:23    5   100  0  15

!    Version 15.0/1.0, Retrans: 0, Retries: 0, Prefixes: 2

!    Topology-ids from peer - 0

!    Stub Peer Advertising ( CONNECTED ) Routes

Task 5.3: Test Query Behavior with Stub Router

! Shut down a route to trigger queries

R6# configure terminal

R6(config)# interface loopback 0

R6(config-if)# shutdown

R6(config-if)# end

! On R1, check if queries were sent to all neighbors

R1# show ip eigrp topology active

! Enable query debugging on R5

R5# debug eigrp packets query

! Notice: R5 does NOT receive queries (stub router)

! Bring R6 loopback back up

R6(config)# interface loopback 0

R6(config-if)# no shutdown

R6(config-if)# end

R5# undebug all

✅ Checkpoint 4: R5 configured as stub router. Queries no longer propagate to R5, reducing query domain and SIA risk.

📝 Step 6: Implement Route Summarization to Limit Query Scope

Route summarization creates query boundaries, preventing queries from propagating beyond the summary point.

Task 6.1: Configure Summarization on R2, R3, R4

! On R2, summarize routes toward R6

R2# configure terminal

R2(config)# interface gigabitethernet 1/0

R2(config-if)# ip summary-address eigrp 100 192.168.0.0 255.255.252.0

R2(config-if)# exit

R2(config)# end

R2# write memory

! On R3, summarize routes toward R6

R3# configure terminal

R3(config)# interface gigabitethernet 1/1

R3(config-if)# ip summary-address eigrp 100 192.168.0.0 255.255.252.0

R3(config-if)# exit

R3(config)# end

R3# write memory

! On R4, summarize routes toward R5

R4# configure terminal

R4(config)# interface gigabitethernet 0/0

R4(config-if)# ip summary-address eigrp 100 192.168.0.0 255.255.252.0

R4(config-if)# exit

R4(config)# end

R4# write memory

📘 Summary Route 192.168.0.0/22:
• Covers 192.168.0.0 through 192.168.3.255
• Includes 192.168.1.0/24, 192.168.2.0/24, 192.168.3.0/24
• Creates Null0 route for loop prevention
• Queries stop at summary boundary

Task 6.2: Verify Route Summarization

! Check for Null0 summary routes

R2# show ip route | include Null0

R3# show ip route | include Null0

R4# show ip route | include Null0

! On R6, verify summary route is received

R6# show ip route 192.168.0.0

! Should show aggregate route 192.168.0.0/22

! Test that specific routes are hidden

R6# show ip route 192.168.1.0 longer-prefixes

! Should show summary, not specific /24 routes

Task 6.3: Test Query Boundary

! On R1, shut down loopback

R1# configure terminal

R1(config)# interface loopback 0

R1(config-if)# shutdown

R1(config-if)# end

! Enable query debugging on R6

R6# debug eigrp packets query

! R6 should NOT receive queries for 192.168.1.0/24

! because R2 and R3 advertised summary

! Restore R1 loopback

R1# configure terminal

R1(config)# interface loopback 0

R1(config-if)# no shutdown

R1(config-if)# end

R6# undebug all

✅ Checkpoint 5: Route summarization configured. Query boundaries established. Queries no longer propagate beyond summary points.

📝 Step 7: Adjust EIGRP Active Timer (Advanced Tuning)

The Active Timer determines how long EIGRP waits for query replies before declaring SIA. Default is 3 minutes (180 seconds).

Task 7.1: View Current Active Timer

R1# show ip protocols | include active

! Default: EIGRP Active Time: 3 min

Task 7.2: Adjust Active Timer (Use with Caution)

! On R1, adjust active timer to 2 minutes

R1# configure terminal

R1(config)# router eigrp 100

R1(config-router)# timers active-time 120

R1(config-router)# exit

R1(config)# end

R1# write memory

! Verify change

R1# show ip protocols | include active

! Should show: EIGRP Active Time: 2 min

⚠️ Active Timer WARNING:
• Decreasing active timer causes faster SIA detection but may lead to premature neighbor resets
• Increasing active timer allows more time for slow replies but delays SIA detection
• Default 180 seconds is appropriate for most networks
• Only adjust if you have slow WAN links or deep network hierarchy
• Changes should be consistent across all routers in AS

Task 7.3: Restore Default Active Timer

! Restore to default (optional)

R1# configure terminal

R1(config)# router eigrp 100

R1(config-router)# no timers active-time

R1(config-router)# exit

R1(config)# end

R1# write memory

📄 Complete Router Configurations with SIA Prevention

R1 - Complete Configuration

!

! R1 Complete Configuration - Lab 12.3

!

hostname R1

!

interface Loopback0

 description ** R1 Internal Network **

 ip address 192.168.1.1 255.255.255.0

!

interface GigabitEthernet0/0

 description ** Link to R2 **

 ip address 203.18.61.1 255.255.255.252

 no shutdown

!

interface GigabitEthernet0/1

 description ** Link to R3 **

 ip address 203.18.61.5 255.255.255.252

 no shutdown

!

interface GigabitEthernet1/0

 description ** Link to R4 **

 ip address 203.18.61.9 255.255.255.252

 no shutdown

!

router eigrp 100

 network 192.168.1.0 0.0.0.255

 network 203.18.61.0 0.0.0.3

 network 203.18.61.4 0.0.0.3

 network 203.18.61.8 0.0.0.3

 eigrp event-log-size 100000

 eigrp log-neighbor-changes

 eigrp log-neighbor-warnings

 no auto-summary

 eigrp router-id 1.1.1.1

!

end

R2 - Complete Configuration (With Summarization)

!

! R2 Complete Configuration - Lab 12.3

!

hostname R2

!

interface Loopback0

 description ** R2 Internal Network **

 ip address 192.168.2.1 255.255.255.0

!

interface GigabitEthernet0/0

 description ** Link to R1 **

 ip address 203.18.61.2 255.255.255.252

 no shutdown

!

interface GigabitEthernet1/0

 description ** Link to R6 **

 ip address 203.18.62.1 255.255.255.252

 ip summary-address eigrp 100 192.168.0.0 255.255.252.0

 no shutdown

!

router eigrp 100

 network 192.168.2.0 0.0.0.255

 network 203.18.61.0 0.0.0.3

 network 203.18.62.0 0.0.0.3

 eigrp event-log-size 100000

 eigrp log-neighbor-changes

 eigrp log-neighbor-warnings

 no auto-summary

 eigrp router-id 2.2.2.2

!

end

R5 - Complete Configuration (Stub Router)

!

! R5 Complete Configuration - Lab 12.3 (EIGRP Stub)

!

hostname R5

!

interface Loopback0

 description ** R5 Internal Network **

 ip address 192.168.5.1 255.255.255.0

!

interface GigabitEthernet0/0

 description ** Link to R4 **

 ip address 203.18.64.2 255.255.255.252

 no shutdown

!

interface GigabitEthernet0/1

 description ** Link to R6 **

 ip address 203.18.65.1 255.255.255.252

 no shutdown

!

router eigrp 100

 network 192.168.5.0 0.0.0.255

 network 203.18.64.0 0.0.0.3

 network 203.18.65.0 0.0.0.3

 eigrp stub connected

 eigrp event-log-size 100000

 eigrp log-neighbor-changes

 eigrp log-neighbor-warnings

 no auto-summary

 eigrp router-id 5.5.5.5

!

end

✅ Comprehensive Verification Commands

1. Verify EIGRP Neighbor Relationships

R1# show ip eigrp neighbors

R1# show ip eigrp neighbors detail

! Check for "Stub Peer" indication on neighbors

2. Verify EIGRP Event Logging

R1# show eigrp address-family ipv4 events

R1# show eigrp address-family ipv4 events | include SIA

! Look for SIA-related events

3. Verify Active/Passive States

R1# show ip eigrp topology

! All routes should be in "P" (Passive) state under normal conditions

R1# show ip eigrp topology active

! Should show no active routes (empty output = good)

4. Verify Stub Router Configuration

R5# show ip protocols | include Stub

! Should show stub configuration

R4# show ip eigrp neighbors detail | include Stub

! Should show R5 as stub peer

5. Verify Route Summarization

R2# show ip route | include Null0

! Should show summary route to Null0

R6# show ip route 192.168.0.0

! Should receive summary route 192.168.0.0/22

6. Verify Active Timer Settings

R1# show ip protocols | include active

! Check active timer value (default 3 min)

7. Monitor EIGRP Traffic

R1# show ip eigrp traffic

! Look for Query, Reply, SIA-Query, SIA-Reply counts

8. Check EIGRP Topology for All Routes

R1# show ip eigrp topology all-links

! Shows all paths including non-successors

9. Verify Query Scope

! Enable debug and trigger route change

R2# debug eigrp packets query

R2# debug eigrp packets reply

! Cause topology change and observe query propagation

! Then disable debug

R2# undebug all

10. Check for SIA History

R1# show eigrp address-family ipv4 sia-statistics

! Shows SIA statistics if available in IOS version

📋 Lab Verification Checklist

☑ All 6 routers have interfaces configured and in "up/up" state
☑ EIGRP AS 100 configured on all routers
☑ EIGRP neighbor relationships established (R1-R2-R3-R4-R5-R6)
☑ All loopback networks reachable from all routers
☑ EIGRP event logging enabled on all routers (size 100000)
☑ Event logs capturing neighbor changes and warnings
☑ SIA condition successfully simulated and observed
☑ SIA events logged in EIGRP event log
☑ R5 configured as EIGRP stub router (connected)
☑ R4 recognizes R5 as stub peer (show neighbors detail)
☑ Route summarization configured on R2, R3, R4
☑ Null0 routes created for summaries (192.168.0.0/22)
☑ R6 receives summary route instead of specific routes
☑ Query boundaries verified at summary points
☑ Stub router does not receive queries
☑ Active timer settings verified (default or adjusted)
☑ No routes in Active state under normal conditions
☑ EIGRP traffic statistics show query/reply activity
☑ End-to-end connectivity maintained after SIA prevention
☑ All configurations saved on all routers

🔧 Comprehensive SIA Troubleshooting Guide

Problem 1: Frequent SIA Occurrences

Symptoms:
• Neighbor relationships frequently resetting
• "Stuck in active" messages in logs
• Routes constantly in Active state
• Network instability and packet loss

Troubleshooting Steps:

! Step 1: Check event logs for SIA patterns

R1# show eigrp address-family ipv4 events | include SIA

! Identify which routes and neighbors are affected

! Step 2: Check current active routes

R1# show ip eigrp topology active

! If many routes are active, investigate why

! Step 3: Check neighbor stability

R1# show ip eigrp neighbors

! Look at uptime - frequent resets indicate issues

! Step 4: Check query/reply statistics

R1# show ip eigrp traffic

! High query counts with low reply counts = problem

! Step 5: Verify network diameter

! Too many hops can cause query timeouts

! Step 6: Check for routing loops

R1# traceroute 192.168.X.1

! Loops cause queries to circulate indefinitely

Solutions:

Cause	Solution
Large network diameter	Implement route summarization at boundaries
Missing feasible successors	Add redundant paths with proper metrics
No stub routing	Configure edge routers as EIGRP stubs
Slow WAN links	Increase active timer or improve bandwidth
Router resource exhaustion	Upgrade router CPU/memory or reduce routing table
Routing loops	Check for misconfigured redistribution or filters

Problem 2: Stub Router Not Preventing SIA

Symptoms:
• Stub router still receiving queries
• SIA still occurring despite stub configuration
• Neighbor not recognizing stub status

Troubleshooting Steps:

! Step 1: Verify stub configuration

R5# show ip protocols | include Stub

! Should show "Routing Protocol is eigrp 100" with Stub indication

! Step 2: Verify neighbor sees stub status

R4# show ip eigrp neighbors detail

! Look for "Stub Peer Advertising" line

! Step 3: Check if queries are being sent

R5# debug eigrp packets query

! Should NOT receive queries

! Step 4: Verify EIGRP is running

R5# show ip eigrp neighbors

! Neighbors must be up for stub to work

! Step 5: Check stub options

R5# show run | section router eigrp

! Verify "eigrp stub" command is present

Solutions:

Cause	Solution
Stub command not configured	Add "eigrp stub connected" under router eigrp
Neighbor relationship down	Troubleshoot neighbor connectivity
Wrong stub options	Use appropriate options (connected, summary, etc.)
Old IOS version	Upgrade to IOS 12.0(7)T or higher
Queries from non-stub neighbor	This is normal - stub only affects query TO stub router

Problem 3: Summary Routes Not Stopping Queries

Symptoms:
• Queries propagating beyond summary boundary
• Specific routes visible despite summary
• Null0 route not created

Troubleshooting Steps:

! Step 1: Verify summary configuration

R2# show run interface gigabitethernet 1/0

! Look for "ip summary-address eigrp" command

! Step 2: Check for Null0 route

R2# show ip route | include Null0

! Should show summary route to Null0

! Step 3: Verify neighbor receives summary

R6# show ip route 192.168.0.0

! Should show aggregate, not specific routes

! Step 4: Check if component routes exist

R2# show ip route 192.168.1.0

! At least one component must exist for summary

! Step 5: Verify correct AS number

! Summary must match EIGRP AS number

Solutions:

Cause	Solution
Summary on wrong interface	Apply summary on outbound interface toward query source
Incorrect summary mask	Recalculate summary to cover component routes
No component routes active	Ensure at least one specific route exists
Wrong AS number in command	Match AS number: ip summary-address eigrp 100
Auto-summary interfering	Use "no auto-summary" under router eigrp

Problem 4: Active Timer Expiring Too Quickly

Symptoms:
• SIA occurring before queries can be answered
• Slow WAN links timing out
• Legitimate neighbors being reset

Troubleshooting Steps:

! Step 1: Check current active timer

R1# show ip protocols | include active

! Default is 3 minutes (180 seconds)

! Step 2: Check network delay

R1# ping 203.18.62.2

! Check round-trip times

! Step 3: Calculate query propagation time

! Query must traverse all hops and return

! Time = (hops × 2 × delay) + processing

! Step 4: Check for packet loss

R1# show interface gigabitethernet 0/0

! Look for output drops or errors

! Step 5: Monitor query timing

R1# debug eigrp packets query

R1# debug eigrp packets reply

! Time between query sent and reply received

Solutions:

Cause	Solution
Slow WAN links	Increase active timer: timers active-time 240
Deep network hierarchy	Implement summarization to reduce query scope
High latency paths	Improve link quality or increase timer
Link congestion	Implement QoS for EIGRP (protocol 88)
Router overload	Reduce routing table size or upgrade hardware

Problem 5: Queries Not Being Answered

Symptoms:
• Queries sent but no replies received
• SIA-Query sent but no SIA-Reply
• Specific neighbor causing SIA

Troubleshooting Steps:

! Step 1: Identify non-responding neighbor

R1# show eigrp address-family ipv4 events | include SIA

! Note which neighbor didn't reply

! Step 2: Check if neighbor is reachable

R1# ping 203.18.61.2

! Basic connectivity test

! Step 3: Check EIGRP traffic on neighbor

R2# show ip eigrp traffic

! Verify queries are being received

! Step 4: Check for ACLs blocking EIGRP

R2# show ip interface gigabitethernet 0/0

! Look for "Outgoing access list" or "Ingoing access list"

! Step 5: Check neighbor topology state

R2# show ip eigrp topology active

! Is neighbor also stuck waiting for replies?

! Step 6: Check for routing loops

R2# show ip eigrp topology | include Active

! Loop can cause query to come back to originator

Solutions:

Cause	Solution
ACL blocking EIGRP	Permit EIGRP (protocol 88) in ACLs
Neighbor waiting for other replies	Implement stub routing to break query chain
Router resource exhaustion	Reduce load or upgrade router
Routing loop	Check split-horizon and route filtering
Link congestion/packet loss	Implement QoS or increase bandwidth
Misconfigured route filtering	Review distribute-lists and route-maps

📚 Key Learning Points & Best Practices

1. Understanding SIA Fundamentals:

✓ SIA occurs when queries don't receive replies within Active Timer (180s default)
✓ DUAL algorithm requires all neighbors to reply to queries
✓ Route must be in Active state waiting for query replies
✓ SIA causes neighbor relationship reset with non-responding routers
✓ Cascading SIA can affect entire network if not prevented
✓ SIA is symptom of design/configuration issues, not EIGRP bug

2. Query Propagation Mechanism:

✓ Queries sent when no Feasible Successor exists
✓ Queries propagate to all EIGRP neighbors except successor
✓ Each router must query its neighbors and wait for replies
✓ Query scope determines convergence time
✓ Large query domains increase SIA risk
✓ Query boundary = point where queries stop propagating

3. EIGRP Stub Routing Benefits:

✓ Prevents queries from being sent to stub routers
✓ Reduces query domain significantly
✓ Ideal for spoke routers in hub-and-spoke topologies
✓ Improves convergence time
✓ Reduces CPU and memory usage on stub routers
✓ Prevents SIA propagation to edge of network
✓ Various stub options for different deployment scenarios

4. Route Summarization for SIA Prevention:

✓ Creates natural query boundaries
✓ Queries stop at summary advertisement point
✓ Reduces routing table size
✓ Improves network scalability
✓ Null0 route prevents routing loops
✓ Should be implemented hierarchically
✓ Critical for large EIGRP deployments

5. Active Timer Considerations:

✓ Default 180 seconds (3 minutes) appropriate for most networks
✓ Increasing timer helps on slow WAN links
✓ Decreasing timer causes faster SIA detection but higher risk
✓ Should be consistent across AS
✓ Not a substitute for proper network design
✓ SIA-Query/Reply mechanism helps with slow links

6. EIGRP Event Logging:

✓ Essential for troubleshooting SIA issues
✓ Captures complete EIGRP FSM transitions
✓ Shows query/reply timing
✓ Identifies problematic neighbors
✓ Should be enabled on all routers
✓ Adjust log size based on network complexity

7. SIA Prevention Best Practices:

✓ Implement EIGRP stub routing at network edges
✓ Configure route summarization at hierarchical boundaries
✓ Design networks with Feasible Successors when possible
✓ Limit network diameter (hop count)
✓ Monitor EIGRP event logs regularly
✓ Implement QoS for EIGRP packets on congested links
✓ Ensure adequate router resources (CPU/memory)
✓ Avoid routing loops through proper design
✓ Use authentication to prevent unauthorized routers

8. Troubleshooting Methodology:

✓ Check event logs first for SIA history
✓ Identify specific routes and neighbors involved
✓ Verify query/reply statistics
✓ Check for routes stuck in Active state
✓ Verify stub and summary configurations
✓ Monitor neighbor stability and uptime
✓ Test query propagation with controlled changes
✓ Use debug commands carefully (high CPU usage)

9. Production Deployment Considerations:

✓ Plan query boundaries before deployment
✓ Document stub and summary locations
✓ Test SIA prevention measures in lab first
✓ Monitor for SIA events proactively
✓ Maintain redundant paths with proper metrics
✓ Review EIGRP topology regularly
✓ Keep IOS versions current for SIA improvements
✓ Implement network monitoring for EIGRP health

10. CCNP Exam Focus:

✓ Understand SIA causes and symptoms
✓ Know how to configure EIGRP stub routing
✓ Understand query propagation mechanism
✓ Know how summarization creates query boundaries
✓ Understand Active Timer and SIA-Query/Reply
✓ Be able to troubleshoot SIA from logs
✓ Know DUAL algorithm and FSM states
✓ Understand relationship between FS and SIA

🎓 Lab Completion Summary

✅ Congratulations!

You have successfully completed Lab 12.3: EIGRP Stuck in Active (SIA) - Troubleshooting & Prevention.

Advanced Skills Mastered:
• Deep understanding of EIGRP SIA condition and causes
• Hands-on experience simulating SIA conditions
• EIGRP event logging and analysis
• EIGRP stub routing implementation
• Route summarization for query scoping
• Active Timer adjustment and tuning
• Comprehensive SIA troubleshooting methodology
• Production-ready SIA prevention techniques

Next Steps:
• Practice all troubleshooting scenarios multiple times
• Experiment with different stub options
• Create intentional SIA conditions for learning
• Review DUAL algorithm and FSM states in detail
• Study SIA-Query and SIA-Reply mechanisms
• Move on to other EIGRP advanced topics (BFD, graceful restart)
• Continue with other routing protocols (OSPF, BGP)

⚠️ Important Final Notes

Production SIA Prevention Guidelines:
• Always implement stub routing at network edges
• Configure route summarization at hierarchical boundaries
• Monitor EIGRP event logs for SIA occurrences
• Design networks to have Feasible Successors
• Limit network diameter to reduce query scope
• Implement QoS for EIGRP protocol packets
• Ensure routers have adequate CPU and memory
• Test failover scenarios in lab before production
• Document all stub and summary configurations
• Keep IOS versions current for SIA improvements

Critical Warnings:
• Never intentionally create SIA in production networks
• Debug commands consume significant CPU - use carefully
• Test all SIA prevention measures in lab first
• Document baseline before making changes
• Have rollback plan before implementing stub/summary
• Schedule changes during maintenance windows
• Monitor network closely after SIA prevention implementation
• Don't rely solely on Active Timer adjustment
• Understand that SIA indicates design issues, not EIGRP bugs
• Cascading SIA can affect entire network - prevent proactively

🏆 End of Lab 12.3 🏆

EIGRP Stuck in Active - Troubleshooting & Prevention

Lab Duration: 120-150 minutes

CCNP Enterprise (ENCOR 350-401 & ENARSI 300-410)

Outstanding work completing this advanced EIGRP SIA lab!
You now have the skills to prevent and troubleshoot one of
the most challenging EIGRP issues in enterprise networks.

Keep practicing and good luck with your CCNP certification journey!

🔐 Access Denied

🏆 End of Lab 12.3 🏆