Specifications

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Cisco Nexus 3000 Series NX-OS Unicast Routing Configuration Guide, Release 5.0(3)U2(2)
OL-25782-02
Chapter 1 Overview
Summary of Layer 3 Unicast Routing Features
• RPF Loose Check—Packets have a verifiable source address in the routers forwarding table and the
source is reachable through a physical interface. The ingress interface that receives the packet need
not match any of the interfaces in the FIB.
Hardware Forwarding
Cisco NX-OS supports distributed packet forwarding. The ingress port takes relevant information from
the packet header and passes the information to the local switching engine. The local switching engine
does the Layer 3 lookup and uses this information to rewrite the packet header. The ingress module
forwards the packet to the egress port. If the egress port is on a different module, the packet is forwarded
using the switch fabric to the egress module. The egress module does not participate in the Layer 3
forwarding decision.
You also use the show platform fib or show platform forwarding commands to display details on
hardware forwarding.
Software Forwarding
The software forwarding path in Cisco NX-OS is used mainly to handle features that are not supported
in hardware or to handle errors encountered during hardware processing. Typically, packets with IP
options or packets that need fragmentation are passed to the CPU. The unicast RIB and the adjacency
manager makes the forwarding decisions based on the packets that should be switched in software or
terminated.
Software forwarding is controlled by control plane policies and rate limiters.
Summary of Layer 3 Unicast Routing Features
This section provides a brief introduction to the Layer 3 unicast features and protocols supported in
Cisco NX-OS.
This section includes the following topics:
• IPv4, page 1-12
• OSPF, page 1-13
• EIGRP, page 1-13
• BGP, page 1-13
• RIP, page 1-13
• Static Routing, page 1-13
• Layer 3 Virtualization, page 1-13
• Route Policy Manager, page 1-14
• First-Hop Redundancy Protocols, page 1-14
• Object Tracking, page 1-14
IPv4
Layer 3 uses the IPv4 protocol. For more information, see Chapter 2, “Configuring IPv4.”