IS-IS was ad hoc in its evolution, whereas OSPF was more formal:
1985: Originally called DECnet Phase V Routing
1988: Adopted by ISO and renamed IS-IS
1990: Publication of RFC 1142, "OSI IS-IS Intradomain Routing 1990: Publication of RFC 1195, "Use of OSI IS-IS for Routing in TCP/ip and Dual Environments"
1991: Cisco IOS Software starts supporting IS-IS
1995: ISPs start adopting IS-IS
2000: Publication of IETF draft "IS-IS Extensions for Traffic Engineering"
2001: Publication of IETF draft "IS-IS Extensions in Support of Generalized MPLS"
CLNS Connectionless Network Service (CLNS)—CLNS performs datagram transport and does not require a circuit to be established before data is transmitted.
IS-IS Variable-length subnet masks (VLSMs). The mask and the prefix are sent in the routing updates.
Redistribution of IP routes into and out of IS-IS.
Summarization of IP routes.
Level 1 ISs are responsible for routing to ESs inside an area. This is similar to OSPF internal nonbackbone routers in a totally stubby area.
Level 2 ISs route between areas only. This is similar to internal backbone routers in OSPF.
Level 1–2 ISs route between areas and the backbone. They participate in the Level 1 intra-area routing and the Level 2 interarea routing. This is the equivalent of Area Border Routers (ABRs) in OSPF.
! interface Serial0 ip address 192.168.120.1 255.255.255.0 ip router isis ! router isis net 49.0001.1921.6800.1005.00
is-type level-1
! !backbone_r1 EIGRP configuration exercise configuration ! ! This file is designed to be copied and pasted into a router that already ! has the previous BSCN configuration files loaded, at the # prompt ! conf t ! no router isis no clns routing ! access-list 1 permit 172.16.10.0 access-list 1 permit 172.16.11.0 route-map passext permit 10 match ip address 1 ! router eigrp 200 redistribute connected metric 10000 100 255 1 1500 route-map passext network 10.0.0.0 !進(jìn)入討論組討論。
