Specifications

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Cisco MWR 2941 Mobile Wireless Edge Router Release 3.5 Software Configuration Guide, Cisco IOS Release 15.1(3)MR
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Chapter 13 Configuring Cisco Express Forwarding
Information About Cisco Express Forwarding
Unresolved Adjacency
When a link-layer header is prepended to a packet, the FIB requires the prepended header to point to an
adjacency corresponding to the next hop. If an adjacency was created by the FIB and not discovered
through a mechanism such as ARP, the Layer 2 addressing information is not known and the adjacency
is considered incomplete or unresolved. Once the Layer 2 information is known, the packet is forwarded
to the RP, and the adjacency is determined through ARP. Thus, the adjacency is resolved.
Cisco Express Forwarding Operation Modes—Central and Distributed
Cisco Express Forwarding can be enabled in Central or Distributed mode. The Cisco MWR 2941
supports Central mode but does not support Distributed mode.
Central Cisco Express Forwarding Mode Operation
You can use central Cisco Express Forwarding mode when line cards are not available for Cisco Express
Forwarding switching, when you need to use features not compatible with distributed Cisco Express
Forwarding switching, or when you are running on a nondistributed platform. When central
Cisco Express Forwarding mode is enabled, the Cisco Express Forwarding FIB and adjacency tables
reside on the RP, and the RP performs the express forwarding.
Figure 13-2 shows the relationship between the routing table, the FIB, and the adjacency table during
central Cisco Express Forwarding mode operation. The Catalyst switches forward traffic from
workgroup LANs to a Cisco 7500 series router on the enterprise backbone running central Cisco Express
Forwarding. The RP performs the express forwarding.
Discard adjacency The router discards the packets.
Drop adjacency The router drops the packets.
Table 13-1 Adjacency Types That Require Special Handling (continued)
Packets of This Adjacency Type Receive This Processing