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(Required) Enable the IS-IS process:
(global) router isis [ area tag ]
This command enables the IS-IS routing protocol. If your router is in multiple IS-IS areas, you need to use the tag option to specify the area associated with the router. Areas are compared between routers to establish levels of domains and how exchanges will be performed.
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(Required) Configure the router ID:
(router) net network-entity-title
This specifies the router's area and system ID. The net ID does not enable routing. It is the ID of the router within the areas defined by the router isis command. A net is a network service access point (NSAP) using a format such as 47.0004.004d.0001. 0000.0c11.1111.00, where the last byte is always 0 (.00). The six bytes directly in front of the n-selector are the system ID (0000.0c11.1111). The system ID length is a fixed size and cannot be changed. The system ID must be unique for each device throughout each area (level 1) and throughout the backbone (level 2). All bytes in front of the system ID are the area ID (47.0004.004d.0001). When IS-IS is used to perform IP routing only, a net must still be configured to define the router system ID and area ID.
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(Optional) Specify the IS-IS router type:
(interface) is-type { level-1 level-1-2 level-2-only } A router can be a level 1 router only (intra-area), a level 2 router (interarea), or both level 1 and level 2.
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(Required) Activate IS-IS routing on the interface:
(interface) ip router isis [ area tag ]
If the router has multiple areas, use the area tag option to specify which area the interface is operating in.
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(Optional) Specify the IS-IS circuit type for the interface:
(interface) isis circuit-type { level-1 level-1-2 level-2-only } Use this command to configure the type of adjacency desired for neighbors on the specified interface. Level 1 adjacencies can be established if the neighbor is configured with a common area. For the level-1-2 option, level 1 and level 2 adjacencies can be established if the routers have a common area; otherwise , only level 2 adjacencies are established (this is the default). For the level-2-only option, only level 2 adjacencies are formed if the neighbors are configured with L2 or L1L2 circuit types.
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(Optional) Set the metric on the IS-IS interface:
(interface) isis metric default-metric { level-1 level-2 } This command specifies the IS-IS cost for this interface. The cost is used to determine the best route. The range is from 0 to 63; the default is 10.
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(Optional) Specify the hello interval:
(interface) isis hello-interval seconds { level-1 level-2 } This command specifies the length of time, in seconds, between hello packets the router sends on the specified interface. The options level-1 and level-2 allow you to set the timer individually for each type, except on a serial interface.
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(Optional) Set the retransmit interval:
(interface) isis retransmit-interval seconds
This command specifies in seconds how long the router waits between retransmission of IS-IS Link State Packets (LSPs) for point-to-point links.
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(Optional) Control the LSP transmission frequency:
(interface) isis lsp-interval seconds
This command allows you to control how often LSP updates are sent out the interface. By setting the seconds option, you specify or control how often LSP updates are sent out the interface on a point-to-point link. This can reduce the amount of overhead on the sending link. Or, if this parameter is changed, it reduces the number of LSPs received by the other side.
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(Optional) Limit the LSP retransmission rate:
(interface) isis retransmit-throttle-interval milliseconds
This command allows you to control how often the same LSP updates are retransmitted out the interface. By setting the milliseconds option, you specify or control how often updates are sent out in a successive manner for the same LSP.
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(Optional) Control adjacency update settings:
(interface) isis hello-multiplier multiplier { level-1 level-2 } This command allows you to control how many packets are missed before the adjacency is considered down. The multiplier is the number of missed packets; the default is 3. The multiplier can be set for level 1 or level 2 routers.
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(Optional) Specify the priority to control which device becomes the designated router:
(interface) isis priority value { level-1 level-2 } This command sets the priority sent out on the interface. The device with the highest priority on a multipoint broadcast interface becomes the designated router for that network. The default setting is 64.
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(Optional) Assign a password to the interface:
(interface) isis password password { level-1 level-2 } By specifying the password, you can control which devices the IS-IS router communicates with. Level 1 and level 2 passwords are set independently and are plain text.
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(Optional) Assign a password to the area:
(router) area password password
All the routers in the area have to be configured with the same password in order to exchange LSPs. The area password is exchanged between level 1 routers within the area.
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(Optional) Assign a password to the domain:
(router) domain-password password
All the routers in the domain have to be configured with the same password in order to exchange LSPs. The domain password is exchanged between level 2 routers within the network.
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(Optional) Summarize between areas:
(router) summary-address address mask { level-1 level-1-2 level-2 } This command allows you to configure summarization for IS-IS routers when performing redistribution from another routing protocol. You can set summaries for each level. By setting summaries, you control the number of entries in the routing table.
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(Optional) Generate a default route:
(router) default-information originate [ route-map map-name ]
This command allows you to inject a default route into the IS-IS area. Whenever you redistribute, the router does not put in a default route automatically. This command allows the default to be generated. You can have the route created conditionally if you use the route-map option.
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See the following sections for information on route-processing features:
This example configures IS-IS for the router Kiddie to be in Area 1 with a device ID of 1. Each interface is configured for integrated IS-IS routing, and a password is configured on Ethernet 0 to prevent unauthorized LSP updates. Also, the priority of the Ethernet 0 interface is set to 90 for level 1 routers so that this router will be the preferred designated router on the segment. RIP routes are redistributed from the 172.16.254.254 subnet from a router running OSPF and are redistributed into IS-IS for level 1 and are summarized on the Class B network address. Figure 7-5 shows the basic layout of the router example.
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