Fast Caching - HP ProCurve Secure 7000dl Series Basic Management And Configuration Manual

IP Routing—Configuring Static Routes
Overview
11-12
The router can share traffic over the routes based on destination, assigning
traffic destined to some hosts to one route and traffic destined to other hosts
to another route. In this case, the traffic may not be exactly balanced over the
multiple connections, but the more sessions the router supports, the more
evenly balanced the traffic will be.
The router can also share the traffic in a round-robin manner, alternating
between the routes every time it routes a new packet to the destination
network. Configuring the router to load share in this way, however, can
cause packets to arrive at the destination out of order and is not generally
recommended.

Fast Caching

One of a router's tasks is to forward the packets it receives with a minimum
of delay. However, the router must also accurately route packets, and looking
up routes takes time and processing power. When a router uses process
switching, it considers route lookup to be no more important than any other
process and forces packets to wait in a queue until it finishes other tasks. When
CPU usage spikes, packets can be delayed longer than acceptable.
Fast caching, or fast-switching cache, is designed to speed processing of
packets that follow often-used routes. In addition to the routing table, the
router keeps a fast-cache table, which contains entries for recently received
packets. A fast-cache entry includes the destination address and the forward-
ing interface. When the router receives a packet, the CPU postpones other
tasks to immediately check the fast-cache table for a matching entry. If the
router finds a matching entry, it rewrites the packet's header and forwards it
to the appropriate interface. (See Figure 11-2.) If the router does not find a
match in the fast-cache table, it sends the packet to the appropriate queue to
await processing. When the router processes these packets, it checks the
routing table to determine where the packets should be forwarded.
On the ProCurve Secure Router, you can enable fast caching for individual
interfaces. However, if you enable the firewall, the ProCurve Secure Router
uses process switching because firewall features can require extensive com-
putations. For example, the firewall must check packets for known cyber
attacks, ensure packet integrity, track connections, and determine if packets
match access control lists (ACLs).