R2511-HP MSR Router Series Layer 3 - IP Services Configuration Guide(V5)

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Configuring fast forwarding
Overview
Fast forwarding reduces route lookup time and improves packet forwarding efficiency by using a
high-speed cache and data-flow-based technology. It uses a five-tuple (source IP address, source port
number, destination IP address, destination port number, and protocol number) to identify a data flow.
After the first packet of a flow is forwarded through the routing table, fast forwarding creates an entry for
the flow and uses the entry to forward subsequent packets of the flow.
Fast forwarding can process fragmented IP packets, but it does not fragment IP packets.
Some features, such as packet queue management and header compression, can decrease fast
forwarding performance.
Fast forwarding is supported:
• On all kinds of high-speed interfaces (including subinterfaces), such as Ethernet, synchronous PPP,
Frame Relay and HDLC interfaces.
• On PPP MP links.
• On IPHC compression or VJ compression enabled PPP links.
• When packet filtering is configured.
• When Application Specific Packet Filter (ASPF) is configured.
• When Network Address Translation (NAT) is configured.
• When Generic Routing Encapsulation (GRE) is configured.
Configuration guidelines
Follow these guidelines when you configure fast forwarding:
• To enable per-packet load balancing, you must disable fast forwarding in the corresponding
direction of related interfaces.
• The interface on which fast forwarding is enabled stops sending ICMP redirect messages.
• After fast forwarding is enabled on an interface, no IP packet debugging information is displayed
for the interface by using the debugging ip packet command.
• To implement fast forwarding for a single data flow, enable fast forwarding in the inbound direction
of the incoming interface and in the outbound direction of the outgoing interface.
• When a routing interface is different from its physical interface on links such as MP links or PPPoE
links, whether fast forwarding is enabled or not on the physical interface does not affect fast
forwarding on the routing interface.
Configuration procedure
To configure fast forwarding: