Is-Is Interfaces - Cisco NCS 6000 Series Configuration Manual

IS-IS Interfaces

IS-IS Interfaces
IS-IS interfaces can be configured as one of the following types:
• Active—advertises connected prefixes and forms adjacencies. This is the default for interfaces.
• Passive—advertises connected prefixes but does not form adjacencies. The passive command is used to
• Suppressed—does not advertise connected prefixes but forms adjacencies. The suppress command is
• Shutdown—does not advertise connected prefixes and does not form adjacencies. The shutdown command
Multitopology Configuration
The software supports multitopology for IPv6 IS-IS unless single topology is explicitly configured in IPv6
address-family configuration mode.
Note IS-IS supports IP routing and not Open Systems Interconnection (OSI) Connectionless Network Service
(CLNS) routing.
IPv6 Routing and Configuring IPv6 Addressing
By default, IPv6 routing is disabled in the software. To enable IPv6 routing, you must assign IPv6 addresses
to individual interfaces in the router using the ipv6 enable or ipv6 address command. See the Network Stack
IPv4 and IPv6 Commands on module of IP Addresses and Services Command Reference for Cisco NCS 6000
Series Routers.
Limit LSP Flooding
Limiting link-state packets (LSP) may be desirable in certain "meshy" network topologies. An example of
such a network might be a highly redundant one such as a fully meshed set of point-to-point links over a
nonbroadcast multiaccess (NBMA) transport. In such networks, full LSP flooding can limit network scalability.
One way to restrict the size of the flooding domain is to introduce hierarchy by using multiple Level 1 areas
and a Level 2 area. However, two other techniques can be used instead of or with hierarchy: Block flooding
on specific interfaces and configure mesh groups.
Both techniques operate by restricting the flooding of LSPs in some fashion. A direct consequence is that
although scalability of the network is improved, the reliability of the network (in the face of failures) is reduced
because a series of failures may prevent LSPs from being flooded throughout the network, even though links
exist that would allow flooding if blocking or mesh groups had not restricted their use. In such a case, the
link-state databases of different routers in the network may no longer be synchronized. Consequences such
as persistent forwarding loops can ensue. For this reason, we recommend that blocking or mesh groups be
used only if specifically required, and then only after careful network design.
Routing Configuration Guide for Cisco NCS 6000 Series Routers, IOS XR Release 6.4.x
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configure interfaces as passive. Passive interfaces should be used sparingly for important prefixes such
as loopback addresses that need to be injected into the IS-IS domain. If many connected prefixes need
to be advertised then the redistribution of connected routes with the appropriate policy should be used
instead.
used to configure interfaces as suppressed.
is used to disable interfaces without removing the IS-IS configuration.
Implementing IS-IS