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router isis
You can configure only one IS-IS routing process to perform Level 2 (interarea) routing. You can
configure this process to perform Level 1 (intra-area) routing at the same time. You can configure up to
29 additional processes as Level 1-only processes. If Level 2 routing is configured on any process, all
additional processes are automatically configured as Level 1.
An interface cannot be part of more than one area, except in the case where the associated routing
process is performing both Level 1 and Level 2 routing. On media such as WAN media where
subinterfaces are supported, different subinterfaces could be configured for different areas.
If Level 2 routing is not desired for a given area, use the is-type command to remove Level 2. Level 2
routing can then be enabled on some other router instance.
Explicit redistribution between IS-IS instances is prohibited (prevented by the parser). In other words,
you cannot issue a redistribute isis area-tag command in the context of another IS-IS router instance
(router isis area-tag). Redistribution from any other routing protocol into a particular area is possible,
and is configured per router instance, as in Cisco IOS software Release 12.0, using the redistribute and
route map commands. By default, redistribution is into Level 2.
If multiple Level 1 areas are defined, the Target Address Resolution Protocol (TARP) behaves in the
following way:
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After you enter the router isis command, you can enter the maximum number of paths. There can be
from 1 to 32 paths.
Examples
The following example configures IS-IS for IP routing, with system ID 0000.0000.0002 and area ID
01.0001, and enables IS-IS to form adjacencies on Ethernet interface 0 and serial interface 0. The IP
prefix assigned to Ethernet interface 0 will be advertised to other IS-IS routers.
router isis tag1
net 01.0001.0000.0000.0002
is-type level-1
!
interface ethernet 0
Cisco MWR 2941 Router Command Reference, Release 15.0(1)MR
386
The locally assigned target identifier gets the network service access point (NSAP) of the Level 2
area, if present.
If only Level 1 areas are configured, the router uses the NSAP of the first active Level 1 area as
shown in the configuration at the time of TARP configuration ("tarp run"). (Level 1 areas are sorted
alphanumerically by tag name, with capital letters coming before lowercase letters. For example,
AREA-1 precedes AREA-2, which precedes area-1.) Note that the target identifier NSAP could
change following a reload if a new Level 1 area is added to the configuration after TARP is running.
The router continues to process all Type 1 and 2 protocol data units (PDUs) that are for this router.
Type 1 PDUs are processed locally if the specified target identifier is in the local target identifier
cache. If not, they are "propagated" (routed) to all interfaces in the same Level 1 area. (The same
area is defined as the area configured on the input interface.)
Type 2 PDUs are processed locally if the specified target identifier is in the local target identifier
cache. If not, they are propagated via all interfaces (all Level 1 or Level 2 areas) with TARP
enabled. If the source of the PDU is from a different area, the information is also added to the local
target identifier cache. Type 2 PDUs are propagated via all static adjacencies.
Type 4 PDUs (for changes originated locally) are propagated to all Level 1 and Level 2 areas
(because internally they are treated as "Level 1-2").
Type 3 and 5 PDUs continue to be routed.
Type 1 PDUs are propagated only via Level 1 static adjacencies if the static NSAP is in one of the
Level 1 areas in this router.
Cisco MWR 2941 Router Command Reference, Release 15.0(1)MR
OL-23890-01
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