Alternative Routes And Route Preferences - Avaya 8800 Configuration Manual

your links between routers to efficiently send IP traffic. ECMP supports and complements the
following protocols and route types:
• OSPF
• RIP
• BGP
• Static routes
• Default routes
For more information about ECMP, see Avaya Ethernet Routing Switch 8800/8600
Configuration — IP Routing, NN46205-523.

Alternative routes and route preferences

Routers can learn several routes to a destination network through several protocols. In the
Avaya Ethernet Routing Switch 8800/8600 software, if the alternative route feature is enabled,
the switch stores the alternative routes sorted in order of network mask, cost, and route
preference. The first route on this list is the best route. The hardware uses the best route. Other
routes are alternative routes.
To avoid traffic interruption, you can globally enable alternative routes to replace the best route
with the next-best route if the best route becomes unavailable. Alternative routes are applied
between routing protocols. For example, if an OSPF route becomes unavailable and an
alternate RIP route is available, it is immediately activated without waiting for an update interval
to expire.
The internal Routing Table Manager records the route changes for protocols. It maintains
separate tables of static (user-configured) and dynamic (protocol-learned) routes. You can
configure preferences that determine the precedence assigned to one type of route over
another.
If a router learns a route with the same network mask and cost values from multiple sources
(protocols), the router uses preferences to select the best route. Up to four other routes for
each destination are held available as alternative routes.
You can configure route preferences for static routes and routing protocols. When you
configure a static route, you can specify a preference for the route. To modify the preference
for a static route, disable the route before you edit the configuration, and then reenable the
route.
Important:
Changing route preferences is a process-intensive operation that can affect system
performance and network reachability while you perform these route preference procedures.
Therefore, Avaya recommends that if you want to change preferences for static routes or
routing protocols, you must do so when you configure routes or before you enable routing
protocols.
Configuration — OSPF and RIP
IP routing features and considerations
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