IS-IS: http://www.ciscopress.com/articles/printerfriendly.asp?p=26850

IS-IS
IP hosts use ARP, not ES-IS; ES-IS enabled automatically
Subnetworks are data-link
Level1 router is only aware of local topology; L2 connects areas
Different hellos for P2P, LAN (pkt specifies L1, L2 or L1-L2)
Hello interval is 10 secs or 3.3 secs for DIS on multi-access links
sysID must be same length on all routers (6 bytes on Cisco)
TLV = Type, Length, Value tuple
Cisco routers support max 3 area addresses (can be changed to 255 recently)
TLV field is appended if authentication required
Multiaccess - nodes broadcast to well-known MACs, elect DIS
separate DISs for L2 & L1 - no backup DIS