Configuring Load Sharing - HP ProCurve Secure 7000dl Series Basic Management And Configuration Manual

IP Routing—Configuring Static Routes

Configuring Load Sharing

11-20
Configuring Load Sharing
Your ProCurve Secure Router may have more than one connection to the same
remote site or to the Internet. However, a router can typically select a single
best route for a destination; without further configuration, traffic destined to
the site will travel over only one of the connections.
For example, your router provides a connection to one ISP through its PPP 1
interface. For redundancy, you connect the router to a second ISP through the
PPP 2 interface. You configure a default route through PPP 1. All Internet
traffic is carried over this WAN connection, and the redundant connection is
unused unless the first connection fails—not a cost-effective solution.
Load sharing allows the router to place up to six routes to the same destination
in its routing table. (See Figure 11-7.) The routes must have the same metric
and administrative distance. When load-sharing is implemented, the router
will sends some traffic over one route and some traffic over the other route.
To enable load sharing, enter this command from the global configuration
mode context:
Syntax: ip load-sharing [per-destination | per-packet]
You can configure the router to balance traffic:
per destination
per packet
When the router balances traffic per destination, it assigns packets to routes
based on the packets' source and destination addresses. That is, when the
router must forward a packet to a destination for which multiple routes exit,
it hashes the packet's source and destination and, according to this value,
assigns the packet to a route. (The router performs the hash function such
that a source and destination can only resolve to as many different values as
routes are available in the routing table.) Therefore, per-destination load
sharing does not balance traffic exactly equally; two successive packets may
be sent over the same route, even if they have different source and destination
addresses. Packets in the same session always take the same route because
they have the same source and destination address. The more traffic that the
router supports, the more evenly it will balance the traffic.