Configuring IS-IS as your IP routing protocol

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This page or section provides device configuration instructions
Please note that the information on this page has not been checked for accuracy and is not intended as a replacement to documentation. Please ensure you understand your desired objectives before attempting to apply any examples listed.

[edit] Why use IS-IS

IS-IS was orignally designed to work with the OSI protocol stack called CLNS. IS-IS was later adapted to carry IPv4 routes and then later again adapted for IPv6. Like OSPF it is a link state protocol and also uses the Dijkstra algorithm.

For a wonderful, indepth article on some key advantages to IS-IS over OSPF please read consult the following URL [1].

[edit] Turning it on

Each router gets assigned a NET. This NET is a CLNS address used to address the router as a whole. We set this under the router isis instance. This CLNS address must be unique.

The Net addres is comprised of

AFI

1 byte

ADI

1-12 bytes

SysID

6 bytes

N-Sel

1 byte

  • AFI is Authority and format indicator. The private AFI is 49
  • ADI is Assigned Domain Identifier 
router isis 
 net 49.0001.0000.000c.00

Like other IGPs we need to define which interfaces to include in is-is. Under OSPF, EIGRP and RIP we use the network command to define which interfaces will participate with the routing protocol. IS-IS uses the 'ip rotuer isis' under the interface sub-configuration mode 

interface Serial3/0
 ip address 10.255.3.2 255.255.255.252
 ip router isis

At this point, with any luck, we should have routes exchanged between routers

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