IS-IS protocol

Can any one help me to understand the difference between IS-IS and OSPF protocol ?

Since both the protocol belongs to "link state" category .what is the exact difference ?

Hey m8,

They are indeed both link state but there are some differences.

OSPF works actually with 6 types of LSA (Link state updates) and multiple area types (5 if I remember correctly)

The IS-IS is based on CLNS and uses only 3 types of LSA's (LSP called in ISIS) which makes the ISIS A bit 'easier'.
It only uses 3 levels (level 1,2 and 1/2.. the other levels previously used are obsolete by now)

Also the AD is different (115 for ISIS and 110 for OSPF)

Also the levels in ISIS can contain upto a 1000 !! routers where OSPF should be capped up to 50.

Just play a bit with ISIS and see for yourself which you prefer. OSPF is still widely the most used protocol I believe (over EIGRP).

Thanks a lot