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After configured IP-link, link cannot automatically redundancy hand over.

Publication Date:  2012-11-15 Views:  29 Downloads:  0
Issue Description
A site of XX country configured two exports: ADSL and 3G link. The ADSL is the main link, customer demands after the main link broken it can hand over to the backup 3G link automatically. Then we use the IP-link function to detect the keep-alive link, through the two equivalent default routes to realize link backup.
But the problem is, when the link recovered, the main link failure only uses the backup 3G link, at the moment the main link recovered, but our company’s firewall didn’t deliver the flow to the main link ADSL immediately, checking firewall found the routing of main link also did not resume.
Alarm Information
Handling Process
Check all configurations, found IP-LINK is not configured wrong. Single go main link ADSL doesn’t have any problems, namely the main link ADSL also has no fault.
Finally found that when the main link is DOWN, because IP-LINK function influences the default route, the default route failure too. In this case, when the main LINK recovery, IP-LINK function has no routing guide to do LINK detection, so firewall think the LINK is still inaccessible, then the default route of the main LINK also will not take effect.
After configured a strict static routing alone for IP-LINK, the fault is recovered.
In the process of data forwarding, according to the addressing forward to traffic network fault problems is a good method.
Root Cause
1. May be the IP-LINK function configured wrong.
2. May be the main link ADSL fault.
3. May be after the IP-LINK function started, there is no routing table guide the IP-LINK to detect.