Route Redistribution; Route Preferences - Avaya P333R-LB User Manual

This can be used for example to load-balance traffic between several firewalls which
serve as the default gateway.

Route Redistribution

Route redistribution is the interaction of multiple routing protocols. OSPF and RIP
can be operated concurrently in P333R-LB. In this case, P333R-LB can be configured
to redistribute routes learned from one protocol into the domain of the other routing
protocol. Similarly, static routes may be redistributed to RIP and to OSPF. Route
redistribution should not be configured carelessly, as it involves metric changes and
might cause routing loops in the presence of other routers with incompatible
schemes for route redistribution and route preferences.
The P333R-LB scheme for metric translation in route redistribution is as follows:
• Static to RIP metric configurable (default 1)
• OSPF internal metric N to RIP metric 1
• OSPF external type 1 metric N to RIP metric 1
• OSPF external type 2 metric N to RIP metric N+1
• Static to OSPF external type 2, metric configurable (default 1)
• RIP metric N to OSPF external type 2, metric N
• Direct to OSPF external type 2, metric 1.
By default, the P333R-LB does not redistribute routes between OSPF and RIP.
Redistribution from one protocol to the other can be configured. Static routes are, by
default, redistributed to RIP and OSPF. P333R-LB allows the user to globally disable
redistribution of static routes to RIP, and separately to globally disable
redistribution of static routes to OSPF. In addition, P333R-LB lets the user configure,
on a per static route basis, whether the route is to be redistributed to RIP and OSPF,
and what metric (in the range of 1-15). The default state is to enable the route to be
redistributed at metric 1. When static routes are redistributed to OSPF, they are
always redistributed as external type 2.

Route Preferences

The routing table may contain routes from different sources. Routes to a certain
destination may be learned independently from RIP and from OSPF, and at the
same time, a static route can also be configured to the same destination. While
metrics are used to choose between routes of the same protocol, protocol
preferences are used to choose between routes of different protocols.
The preferences only apply to routes for the same destination IP address and mask.
They do not override the longest-match choice. For example, a high-preference
static default route will not be preferred over a RIP route to the subnet of the
destination.
Avaya P333R-LB User's Guide
Chapter 1 Overview
9