System information

Configuring IS-IS
10-1
Overview
The integrated Intermediate System to Intermediate System (IS-IS) is a link state
based intra-domain routing protocol used to build a complete and consistent picture of
a network’s topology by sharing link state information across all network
Intermediate System (IS) devices. IS-IS is based on an SPF routing algorithm and
shares all the advantages common to other link-state protocols. It also routes both IP
packets and pure OSI packets with no extra encapsulation by design. IS-IS supports
type of service (TOS) identifiers, IP subnetting, variable subnet masks, external
routing, and authentication.
IS-IS routing decisions are made on two levels. Level 1 routers know the topology of
their network within an area and level 2 routers are used to route between different
areas within a routing domain. If a level 1 router has no knowledge of a specific
destination address, it passes the traffic to a level 2 router. Level 2 routers know which
addresses are reachable through each Level 2 router, and they do not need to know the
topology within Level 1 areas. Level 2 routers can also exchange information with
external routers outside their routing domain.
The following task is required to implement IS-IS on your network:
• Enabling IS-IS
• Redistributing Routes into IS-IS
The following optional tasks are used to manage IS-IS on your network:
• Managing IS-IS on the BSR
• Configuring IS-IS on an Interface
• Gathering IS-IS Information
Enabling IS-IS
You must enable the IS-IS process and assign IS-IS to a specific interfaces in order to
implement IS-IS on your network.
Follow these steps to enable IS-IS on the router: