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IS-IS (Intermediate System to Intermediate System) is a crucial link-state routing protocol often used in service provider networks and modern architectures like Cisco SDA (Software-Defined Access) and VXLAN/EVPN networks. Unlike OSPF, IS-IS does not rely on a backbone area and allows routers to belong to a single area, with multiple areas linked through continuous Layer 2 connections. It uses LSPs (Link-State Packets) instead of LSAs (Link-State Advertisements) and handles multi-access networks differently, employing DIS (Designated Intermediate System) instead of DR/BDR (Designated Router/Backup Designated Router).
You Should Know:
1. Basic IS-IS Configuration on Cisco Devices:
router isis net 49.0001.0000.0000.0001.00 is-type level-2-only interface GigabitEthernet0/1 ip router isis
This configures IS-IS on a Cisco router, setting the NET (Network Entity ) and enabling IS-IS on an interface.
2. Verifying IS-IS Adjacencies:
show isis neighbors
This command displays IS-IS neighbor adjacencies, ensuring proper protocol operation.
3. Viewing IS-IS Database:
show isis database
This command lists the IS-IS link-state database, showing LSPs received from neighboring routers.
4. Enabling IPv6 Support in IS-IS:
router isis address-family ipv6
This enables IPv6 routing within the IS-IS process.
5. Troubleshooting IS-IS:
debug isis adj-packets
Use this command to debug IS-IS adjacency formation issues.
6. Changing IS-IS Metric:
interface GigabitEthernet0/1 isis metric 50 level-2
This adjusts the IS-IS metric for a specific interface.
7. IS-IS Authentication:
interface GigabitEthernet0/1 isis password securepassword level-2
This adds authentication to IS-IS adjacencies for enhanced security.
8. Viewing IS-IS Route Information:
show isis route
This command displays the IS-IS routing table.
9. IS-IS Multi-Area Configuration:
router isis area-tag 49.0002
This configures multiple IS-IS areas on a single router.
10. IS-IS TLV Extensions:
IS-IS uses TLVs (Type-Length-Values) for extensibility, supporting features like IPv6 and MPLS.
What Undercode Say:
IS-IS is a powerful and flexible routing protocol, especially suited for large-scale networks like service provider backbones and modern data center architectures. Its simplicity in area design, extensibility through TLVs, and efficient handling of multi-access networks make it a preferred choice over OSPF in many scenarios. By mastering IS-IS configuration and troubleshooting commands, network engineers can ensure robust and scalable network designs. For further reading, check out the Cisco IS-IS Study Guide.
Related Commands:
- Linux Networking:
ip route show
Displays the routing table on Linux systems.
- Windows Networking:
route print
Shows the routing table on Windows.
- Packet Capture (Linux):
tcpdump -i eth0 -n proto 89
Captures IS-IS packets (protocol 89) on a Linux interface.
Packet Capture (Windows):
Use Wireshark with the filter `isis` to capture IS-IS traffic.
By integrating these commands and steps, you can effectively deploy and manage IS-IS in your network environment.
References:
Reported By: Danieldib Is – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
