Name: See IS-IS routing and its topology overlay
Uploaded: 2026-10-05
Duration: PT264.45S

See IS-IS routing and its topology overlay

Configure a Level 2 IS-IS process on two prepared routers, enable it on the connected and loopback interfaces, and save the configuration. Verify the neighbor, learned route and real traffic, then use the IS-IS display filter to show or hide orange adjacency indicators. Disconnect and restore the same cable to diagnose and confirm recovery. The animated indicators represent protocol activity; they are not captured packets. This episode covers one connected Level 2 pair.

English narration and on-screen explanations. Read the narration transcript.

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Start with a connected pair
R1 and R2 are connected on Gi0/0. Each router also has a loopback address.
The directly connected address replies, but the remote loopback has no route
yet.
Configure IS-IS on both routers
R1 uses process CORE and a unique NET. Both routers use Level 2.
Enable IS-IS on the cable and loopback interfaces, then save the
configuration.
R2 uses process CORE and a unique NET. Both routers use Level 2.
Enable IS-IS on the cable and loopback interfaces, then save the
configuration.
Verify the neighbor, route and traffic
The neighbor is UP. The i L2 entry is the learned route to R2’s loopback.
The remote loopback now replies with 100 percent success.
Show and hide IS-IS indicators
The orange IS-IS indicators show the active adjacency on this link.
This checkbox changes the display. It does not disable IS-IS on the routers.
Recognize a failed link
Confirm the exact connection before disconnecting it.
The physical interface is down, the neighbor is gone, and the remote route is
absent.
Restore the connection and confirm
Reconnect R1 and R2 on the same Gi0/0 ports.
Verify the recovered neighbor, learned route, and successful traffic.
The IS-IS indicators return when the adjacency is healthy again.