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Cisco Nexus 7000 Series NX-OS Unicast Routing Configuration Guide, Release 4.x
OL-20002-02
Chapter 1 Overview
Cisco NX-OS Fowarding Architecture
• Hardware Forwarding, page 1-12
• Software Forwarding, page 1-12
Unicast RIB
The Cisco NX-OS forwarding architecture consists of multiple components, as shown in Figure 1-4.
Figure 1-4 Cisco NX-OS Forwarding Architecture
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 (FIB) on the supervisors and modules by using the services of 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).
Adjacency Manager
The adjacency manager exists on the active supervisor and maintains adjacency information for different
protocols including ARP, Neighbor Discovery Protocol (NDP), and static configuration. The most basic
adjacency information is the layer 3 to layer 2 address mapping discovered by these protocols. Outgoing
layer 2 packets use the adjacency information to complete the layer 2 header.
The adjacency manager can trigger ARP requests to find a particular layer 3 to layer 2 mapping. The new
mapping becomes available when the corresponding ARP reply is received and processed. For IPv6, the
adjacency manager finds the layer 3 to layer 2 mapping information from NDP. See Chapter 3,
“Configuring IPv6.”
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