Mesh Groups; Overload Bit; Route Summarization - Cisco Nexus 7000 Series Configuration Manual

Information about IS-IS
S e n d d o c u m e n t c o m m e n t s t o n e x u s 7 k - d o c f e e d b a c k @ c i s c o . c o m .
To provide protection against passive attacks, IS-IS never sends the MD5 secret key as cleartext through
the network In addition, IS-IS includes a sequence number in each packet to protect against replay
attacks.
You can use also keychains for hello and LSP authentication. See Cisco Nexus 7000 Series NX-OS
Security Configuration Guide, Release 4.x for information on keychain management.

Mesh Groups

A mesh group is a set of interfaces in which all routers reachable over the interfaces have at least one
link to every other router. Many links can fail without isolating one or more routers from the network.
In normal flooding, an interface receives a new LSP and floods the LSP out over all other interfaces on
the router. With mesh groups, when an interface that is part of a mesh group receives a new LSP, the
interface does not flood the new LSP over the other interfaces that are part of that mesh group.
You may want to limit LSPs in certain mesh network topologies to improve network scalability. Limiting
Note
LSP floods may also reduce the reliability of the network (in case of failures). For this reason, we
recommend that you use mesh groups only if specifically required, and then only after careful network
design.
You can also configure mesh groups in block mode for parallel links between routers. In this mode, all
LSPs are blocked on that interface in a mesh group after the routers initially exchange their link-state
information.

Overload Bit

IS-IS uses the overload bit to tell other routers not to use the local router to forward traffic but to continue
routing traffic destined for that local router.
You may want to use the overload bit in these situations:
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Route Summarization

You can configure a summary aggregate address. Route summarization simplifies route tables by
replacing a number of more-specific addresses with an address that represents all the specific addresses.
For example, you can replace 10.1.1.0/24, 10.1.2.0/24, and 10.1.3.0/24 with one summary address,
10.1.0.0/16.
If more specific routes are in the routing table, IS-IS advertises the summary address with a metric equal
to the minimum metric of the more specific routes.
Cisco NX-OS does not support automatic route summarization.
Note
Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 4.x
9-4
The router is in a critical condition.
Graceful introduction and removal of the router to/from the network.
Other (administrative or traffic engineering) reasons. For example, to wait for BGP convergence.
Chapter 9 Configuring IS-IS
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