362 CHAPTER 22: CONFIGURING IP PERFORMANCE
Configure Fast Forwarding Message forwarding efficiency is a key feature evaluating router performance.
According to regular flow, when a message arrives, the router will copy it from the
interface memory to the main CPU. The CPU specifies the network ID from the IP
address, consults with the routing table to get the best path to forward the
message, and creates MAC frame suitable for output of the message. The created
MAC frame is copied to the output queue via DMA (Direct Memory Access), and
during this process the main system bus is passed twice. This process can be
repeated for message forwarding.
In the Fast forwarding, cache is used to process messages. After the first message
is forwarded by searching routing table, corresponding exchange information is
generated in the cache, and forwarding of the following same messages can be
realized by directly searching the cache. This practice greatly simplifies the queuing
of IP messages, cuts down the route finding time and improves forwarding
throughput of IP messages. Since the forwarding table in the cache has been
optimized, much quicker searching speed can be obtained.
The 3Com Router supports Fast forwarding on various high-speed link interfaces,
such as Ethernet, synchronous PPP, frame relay and HDLC.
Besides, the 3Com Router also supports Fast forwarding when firewall is
configured.
Fast forwarding implemented via the 3Com Router contains the following
features:
■Support fast forwarding on all types of high-speed link interfaces, including
Ethernet, synchronous PPP, frame-relay and HDLC etc.
■Provide fast forwarding when the firewall is configured.
■Support load sharing and improve packets forwarding efficiency greatly.
The performance of Fast forwarding sometimes will be affected by some
characteristics such as message queue management and message header
compression. Fast forwarding is not conducted for fragmented messages.
Fast-forwarding Configuration includes:
■Enable/Disable fast-forwarding on an interface
■Configure fast-forwarding table size
1Enable/Disable fast-forwarding on an interface
You can disable fast-forwarding as needed. For example, if load sharing is required
when forwarding packets, fast-forwarding should be disabled in the forwarding
direction of the interface.
Perform the following configuration in interface view.
Tabl e 395 Enable/Disable fast-forwarding on an interface
Operation Command
Enable fast-forwarding in both directions of the
interface ip fast-forwarding
Enable fast-forwarding on the inbound interface ip fast-forwarding inbound
Enable fast-forwarding on the outbound interface ip fast-forwarding outbound