Cisco Nexus 7000 Series - Layer 3 Consistency Checker; Dynamic TCAM Allocation

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15-2
Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 4.x
OL-20002-02
Chapter 15 Managing the Unicast RIB and FIB
Information About the Unicast RIB and FIB
The unicast RIB exists on the active supervisor. It maintains the routing table with directly connected
routes, static routes, and routes learned from dynamic unicast routing protocols. The unicast RIB also
collects adjacency information from sources such as the Address Resolution Protocol (ARP). The
unicast RIB determines the best next hop for a given route and populates the unicast forwarding
information bases (FIBs) on the modules by using the services of the unicast FIB distribution module
(FDM).
Each dynamic routing protocol must update the unicast RIB for any route that has timed out. The unicast
RIB then deletes that route and recalculates the best next hop for that route (if an alternate path is
available).
This section includes the following topics:
• Layer 3 Consistency Checker, page 15-2
• Dynamic TCAM Allocation, page 15-2
• Virtualization Support, page 15-3
Layer 3 Consistency Checker
In rare instances, an inconsistency can occur between the unicast RIB and the FIB on each module. In
Cisco NX-OS Release 4.0(3) and later releases, Cisco NX-OS supports the Layer 3 consistency checker.
This feature detects inconsistencies between the unicast IPv4 RIB on the supervisor module and the FIB
on each interface module. Inconsistencies include the following:
• Missing prefix
• Extra prefix
• Wrong next-hop address
• Incorrect Layer 2 rewrite string in the ARP or neighbor discovery (ND) cache
The Layer 3 consistency checker compares the FIB entries to the latest adjacency information from the
Adjacency Manager (AM) and logs any inconsistencies. The consistency checker then compares the
unicast RIB prefixes to the module FIB and logs any inconsistencies. See the “Triggering the Layer 3
Consistency Checker” section on page 15-9.
You can then manually clear any inconsistencies. See the “Clearing Forwarding Information in the FIB”
section on page 15-10.
Dynamic TCAM Allocation
Cisco NX-OS divides the FIB to support multiple address families. The FIB TCAM has 128K physical
entries.
Table 15-1 describes the default FIB TCAM allocation.
Table 15-1 Default FIB TCAM Allocation
Region Default Number of Routes Number of TCAM blocks Entry size
IPv4 unicast routes 56K 7 72 bits