关于IS-IS 的历史
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 Protocol"
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"
谁来使用IS-IS
IS-IS主要是电信运营商和大型ISP所普遍采用的一种路由协议。ISP在IGP协议中大量采用IS-IS或者OSPF协议，至于这两种协议哪种更有优势，只能说每个网络工程师都有自己所长，有些习惯使用OSPF，有些就善于组建IS-IS的网络。
面向对象连接和非面向对象连接
面向对象连接就是在数据通过前首先要建立连接，而非面向对象连接则可以不需要建立连接直接发送数据
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.
源码:----------------------------------------------------------
NSAP Examples
The following examples illustrate how an NSAP address is interpreted by IS-IS and ISO-IGRP.
The NSAP 49.0001.aaaa.bbbb.cccc.00 consists of the following:
For IS-IS:
Area = 49.0001
System ID = aaaa.bbbb.cccc
N-selector = 00
For ISO-IGRP:
Domain = 49
Area = 0001
System ID = aaaa.bbbb.cccc
N-selector = ignored by ISO-IGRP
The NSAP 39.0f01.0002.0000.0c00.1111.00 consists of the following:
For IS-IS:
Area = 39.0f01.0002
System ID = 0000.0c00.1111
N-selector = 00
For ISO-IGRP:
Domain = 39.0f01
Area = 0002
System ID = 0000.0c00.1111
N-selector = ignored by ISO-IGRP
--------------------------------------------------------------------------------
基本配置
hostname R1
!
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
!
