If you are comfortable with OSPF, you are already halfway to mastering IS-IS. While OSPF is a common choice for VXLAN EVPN underlays, Cisco ACI relies entirely on IS-IS to build its fabric.
In this video, I break down the IS-IS Overview in a simple way. We use your existing OSPF knowledge as a reference point to make the transition to IS-IS as easy and logical as possible.
Summary
- IS-IS is a “Router-to-Router” communication protocol similar to OSPF (Link-State).
- IS-IS was defined in ISO 10589 for CLNS. RFC 1195 defines how to use IS-IS for routing TCP/IP (Integrated IS-IS).
- IS-IS PDUs reside directly behind the Ethernet frame header (802.3).
- IS-IS Levels Resulting Adjacency Summary:
| 1st Neighbor’s Level | 2nd Neighbor’s Level | Resulting Adjacency |
|---|---|---|
| Level-1 only | Level-1 only | Level-1 (if area matches) |
| Level-1 only | Level-1- 2 | Level-1 (if area matches) |
| Level-1 only | Level-2 only | No adjacency |
| Level-1- 2 | Level-1- 2 | Level-1 (if area matches) Level-2 |
| Level-1- 2 | Level-2 only | Level-2 |
| Level-2 only | Level-2 only | Level-2 |
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