Complete Cisco IS-IS Multi Area Routing Lab Part 3
Welcome to Part 3 of the Complete Cisco IS-IS Multi Area Routing series.
In Part 1, we built the complete IS-IS multi-area topology. In Part 2, we configured DIS election, MPLS Traffic Engineering support, authentication and inter-area connectivity.
Part 3 focuses on advanced multi-protocol routing integration using:
- IS-IS
- EIGRP
- OSPF
- Mutual redistribution
- Route exchange
- Seed metrics
- Routing domain integration
🎯 What You Will Learn
- Level-1 and Level-2 IS-IS routing
- EIGRP integration with IS-IS
- OSPF integration with IS-IS
- Mutual redistribution
- Seed metric configuration
- Routing table verification
- Route propagation concepts
- Troubleshooting redistribution
Table of Contents
Task 1 - Configure IS-IS Area 49.0000
Routers R1, R2 and R3 belong to Area 49.0000.
All routers are configured as Level-2 routers.
Level-2 Routing Concept
$$ Level\text{-}2 = InterArea\ Backbone $$Level-2 routers exchange routes between multiple IS-IS areas.
R1 Configuration
router isis net 49.0000.1111.1111.1111.00 is-type level-2 interface loopback0 ip router isis interface e0/0 ip router isis interface e0/1 ip router isis
R2 Configuration
router isis net 49.0000.2222.2222.2222.00 is-type level-2 interface loopback0 ip router isis interface e0/0 ip router isis interface e0/1 ip router isis
R3 Configuration
router isis net 49.0000.3333.3333.3333.00 is-type level-2 interface loopback0 ip router isis interface e0/0 ip router isis interface e0/1 ip router isis
💡 Important Concept
Level-2 routers form the IS-IS backbone. All inter-area communication depends on Level-2 routing.
Task 2 - Configure IS-IS Area 49.0010
This area contains:
- R4
- R10
- R11
R10 and R11 operate as Level-1 routers. R4 operates as a Level-1-2 router.
Area Reachability
$$ L1\ Routers \rightarrow Local\ Area $$ $$ L1\text{-}L2\ Routers \rightarrow InterArea\ Access $$R4 Configuration
router isis net 49.0010.4444.4444.4444.00 interface loopback0 ip router isis interface e0/0 ip router isis interface e0/1 ip router isis
R10 Configuration
router isis net 49.0010.1010.1010.1010.00 is-type level-1 interface loopback0 ip router isis interface e0/0 ip router isis interface e0/1 ip router isis
R11 Configuration
router isis net 49.0010.0011.0011.0011.00 is-type level-1 interface loopback0 ip router isis interface loopback1 ip router isis interface loopback2 ip router isis interface loopback3 ip router isis interface e0/0 ip router isis
Understanding R4
R4 does not explicitly define an IS type. Cisco IOS therefore treats R4 as a Level-1-2 router.
Task 3 - Configure IS-IS Area 49.0020
Routers R5 and R6 belong to Area 49.0020.
Both routers operate as Level-2 routers.
R5 Configuration
router isis net 49.0020.5555.5555.5555.00 is-type level-2 interface loopback0 ip router isis interface e0/0 ip router isis interface e0/1 ip router isis
R6 Configuration
router isis net 49.0020.6666.6666.6666.00 is-type level-2 interface loopback0 ip router isis interface e0/0 ip router isis
IS-IS Topology Logic
$$ Area\ 49.0000 \leftrightarrow 49.0010 \leftrightarrow 49.0020 $$Task 4 - Configure EIGRP AS 111
EIGRP is configured between:
- R1
- R7
- R8
This creates a separate routing domain.
EIGRP Composite Metric Formula
$$ Metric = 256 \times \left(\frac{10^7}{Bandwidth} + Delay\right) $$R1 Configuration
router eigrp 111 network 192.1.17.0 network 192.1.18.0 network 11.0.0.0
R7 Configuration
router eigrp 111 network 192.1.17.0 network 7.0.0.0 network 107.0.0.0
R8 Configuration
router eigrp 111 network 192.1.18.0 network 8.0.0.0
💡 Why EIGRP Needs Redistribution
EIGRP and IS-IS are different routing protocols. Without redistribution, they cannot exchange routes.
Task 5 - Configure OSPF Area 0
OSPF is configured between R6 and R9.
OSPF Cost Formula
$$ Cost = \frac{Reference\ Bandwidth}{Interface\ Bandwidth} $$R6 Configuration
router ospf 1 network 192.1.69.0 0.0.0.255 area 0 network 66.0.0.0 0.255.255.255 area 0
R9 Configuration
router ospf 1 network 192.1.69.0 0.0.0.255 area 0 network 9.0.0.0 0.255.255.255 area 0
Why OSPF Uses Wildcard Masks
OSPF network commands use wildcard masks instead of subnet masks.
Task 6 - Mutual Redistribution
Redistribution allows different routing protocols to exchange routing information.
This enables end-to-end connectivity across:
- IS-IS
- EIGRP
- OSPF
Redistribution Logic
$$ IS\text{-}IS \leftrightarrow EIGRP \leftrightarrow OSPF $$R1 Redistribution Configuration
IS-IS Side
router isis redistribute eigrp 111
EIGRP Side
router eigrp 111 redistribute isis metric 10 10 10 10 10
EIGRP Seed Metric
$$ Metric = BW + Delay + Reliability + Load + MTU $$R6 Redistribution Configuration
IS-IS Side
router isis redistribute ospf 1
OSPF Side
router ospf 1 redistribute isis subnets
💡 Important Redistribution Rule
EIGRP requires a seed metric during redistribution. Without a metric, redistributed routes will not enter the EIGRP topology table.
Verification Commands
Verify IS-IS Neighbors
show isis neighbors
R4# show isis neighbors System Id Type Interface State R10 L1 Et0/0 UP R11 L1 Et0/1 UP
Verify EIGRP Neighbors
show ip eigrp neighbors
R1# show ip eigrp neighbors Address Interface Hold Uptime 192.1.17.7 Et0/0 12 00:10:22
Verify OSPF Neighbors
show ip ospf neighbor
R6# show ip ospf neighbor Neighbor ID State Interface 9.9.9.9 FULL Ethernet0/0
Verify Redistribution
show ip route
R1# show ip route i L2 66.0.0.0/8 D EX 9.0.0.0/8 O E2 11.0.0.0/8
Routing Domain Exchange
$$ Routes_{IS\text{-}IS} + Routes_{EIGRP} + Routes_{OSPF} $$ $$ = Full\ Network\ Reachability $$Related Articles
Conclusion
Part 3 introduced advanced routing integration concepts including:
- IS-IS Level-1 and Level-2 routing
- EIGRP integration
- OSPF integration
- Mutual redistribution
- Seed metrics
- Route propagation
- End-to-end reachability
Redistribution is one of the most critical skills for enterprise and service provider engineers because real-world networks often contain multiple routing protocols.
Understanding route exchange behavior, metrics and routing domain interaction is essential for advanced troubleshooting and architecture design.
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