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9-5
Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 4.x
OL-20002-02
Chapter 9 Configuring IS-IS
Information about IS-IS
Route Redistribution
You can use IS-IS to redistribute static routes, routes learned by other IS-IS autonomous systems, or
routes from other protocols. You must configure a route map with the redistribution to control which
routes are passed into IS-IS. A route map allows you to filter routes based on attributes such as the
destination, origination protocol, route type, route tag, and so on. For more information, see Chapter 16,
“Configuring Route Policy Manager.”
Whenever you redistribute routes into an IS-IS routing domain, Cisco NX-OS does not, by default,
redistribute the default route into the IS-IS routing domain. You can generate a default route into IS-IS,
which can be controlled by a route policy.
You also configure the default metric that is used for all imported routes into IS-IS.
Load Balancing
You can use load balancing to allow a router to distribute traffic over all the router network ports that are
the same distance from the destination address. Load balancing increases the utilization of network
segments and increases effective network bandwidth.
Cisco NX-OS supports the Equal Cost Multiple Paths (ECMP) feature with up to 16 equal-cost paths in
the IS-IS route table and the unicast RIB. You can configure IS-IS to load balance traffic across some or
all of those paths.
Virtualization Support
Cisco NX-OS supports multiple instances of the IS-IS protocol that runs on the same system. IS-IS
supports Virtual Routing and Forwarding instances (VRFs). VRFs exist within virtual device contexts
(VDCs). You can configure up to four IS-IS instances in a VDC.
By default, Cisco NX-OS places you in the default VDC and default VRF unless you specifically
configure another VDC and VRF. See the Cisco Nexus 7000 Series NX-OS Virtual Device Context
Configuration Guide, Release 4.xe and Chapter 14, “Configuring Layer 3 Virtualization.”
High Availability and Graceful Restart
Cisco NX-OS supports RFC 3847 for graceful restart of IS-IS. IS-IS automatically restarts if the process
experiences problems. After the restart, IS-IS initiates a graceful restart so that the platform is not taken
out of the network topology. If you manually restart IS-IS, it performs a graceful restart and applies the
running configuration.
Note You must enable graceful restart to support in-service software upgrades (ISSU) for IS-IS. If you disable
graceful restart, Cisco NX-OS issues a warning that ISSU cannot be supported with this configuration.
Multiple IS-IS Instances
Cisco NX-OS supports a maximum of four instances of the IS-IS protocol that run on the same node.
You cannot configure multiple instances over the same interface. Every instance uses the same system
router ID.
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