OSPF IS-IS comparison
The following is a comparison of the OSPF and IS-IS routing protocols:
Similarities
- Link state protocols
- Use the Dijkstra algorithm for computing the best path
- Support variable-length subnet masks
- Use Multicast to discover neighboring routers
- Support authentication of routing updates
- Build a topological representation of the network
Differences
OSPF
- is natively built to initially route IPv4 and later IPv6
- is a Layer 3 protocol that runs on top of IP
- uses IP to relay OSPF messages
- employs areas
- ABR routers can be in multiple areas, thus the border between areas is in the router itself
- requires an area 0 backbone
- has a larger set of extensions and optional features specified in the protocol standards
IS-IS
- is an OSI Layer 2 protocol
- does not use IP to carry routing information messages
- employs the use of Level 1 (intra-area), Level 2 (inter-area) or Level 1-2 (both) routers
- area borders exist between routers designated as Level 2 or Level 1-2
- does not require a backbone area
- fewer extensions and options, but more scalable and expandable