Dynamic; Ynamic Route Backup Onfiguration; Overview; Concept - 3Com MSR 50 Series Configuration Manual

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Overview

Concept

Features

D
YNAMIC
C
ONFIGURATION
n
Currently, the dynamic route backup function is available to the following dialup
interfaces: dialer interfaces, PRI interfaces, BRI interfaces, serial interfaces
operating in the asynchronous mode, AM interface, and AUX interfaces.
As a new way of route backup, the dynamic route backup function adopts dial
control center (DCC) to dynamically maintain dialup links, that is, the dynamic
route backup function implements route-based dialup backup.
The dynamic route backup function combines the backup function and the
routing function well, proving reliable connections and standard dial-on-demand
services.
The dynamic route backup function is mainly used to backup dynamic routes, and
moreover, it can also backup static routes and directly-connected routes.
The dynamic route backup function is not dedicated a specific interface or link,
and it is appropriate for implementations with multiple interfaces and multiple
routers.
With the dynamic route backup function enabled, the backup link will be started
automatically when the primary link disconnects, causing no dialup delay
(excluding the time for route convergence).
The dynamic route backup function is independent of specific routing protocols,
and it can collaborate with routing information protocol version 1 (RIP-1), RIP-2,
open shortest path first (OSPF), intermedia system-intermedia system (IS-IS),
border gateway protocol (BGP) and so on. However, some routing protocols (such
as BGP) use the preferred routes by default. When the backup link is activated
after the primary link to the monitored network segment is disconnected, it will
learn routes to the monitored network segment through BGP. When the primary
link is activated again, it will learn routes to the monitored network segment
through BGP. However, the routes that the primary link learn may not be the
preferred routes, so the routes learned by the backup link may continue to be
used. In this case, dynamic route monitoring fails, and the backup link cannot be
hanged up even after the primary link restores.
For BGP, you need to take the following measures to solve this problem:
Assign a higher IP address to the backup link that that to the primary link
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R B
OUTE ACKUP