Dialer watch

Unanswered Question
Jan 17th, 2010

Hi;

I want to know if I can backup to secondary link even if the primary link is still active.when I watch a subnet in my routing table.

Primary interface:serial

Secondary int: Bri

Routage: EIGRP

Thanks all.

I have this problem too.
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Giuseppe Larosa Sun, 01/17/2010 - 13:53

Hello Mosmos_95,

dialer watch reacts only to the missing of watched subnet(s).

if other side of primary link make its side passive (human error) or remove a network statement under router eigrp that includes primary link, dialer watch will trigger the backup link to start.

EIGRP will detect a missing neighbor in 3 hello intervals on the primary path and will remove routes learned from the dead neighbor.

But, if primary link is up and EIGRP adjacency on primary link is fine, dialer watch is not triggered.

If both links are on the same router, you can use the backup command to trigger backup when a specific load threshold is reached.

Hope to help

Giuseppe

mosmos_905 Mon, 01/18/2010 - 02:24

hi guistar

thanks for your reply.

So if I understand

Dialer watch will trigger the backup link to start if it missing the watched subnet. even if the primary link is up and EIGRP adjacency on primary link is fine.

if no can you tell me how I use IP SLA with EIGRP????

Thanks

I will HOPE.

Giuseppe Larosa Mon, 01/18/2010 - 05:33

Hello Mosmos,

yes the trigger is the fact that watched routes disappear from IP routing table, this can happen even if primary link is up and EIGRP adajcency ip up if someone use a route filter on the other side or for other reasons.

combining IP SLA and EIGRP is not possible I think. you can combine IP SLA with static routes using reliable static routing.

see

http://www.cisco.com/en/US/docs/ios/12_3/12_3x/12_3xe/feature/guide/dbackupx.html

However, dialer watch should need a dynamic routing protocol and it is well suited when primary and backup paths are on different routers.

Actually, dialer watch can be used also with static routes according to 12.4T dial config guide

http://www.cisco.com/en/US/partner/docs/ios/dial/configuration/guide/dia_backup_dia_watch_ps6441_TSD_Products_Configuration_Guide_Chapter.html

It is also explained the conditions of trigger for dialer watch:

Monitoring the watched routes is done in the following sequence:

1. Whenever a watched route is deleted, Dialer Watch checks whether there is at least one valid route for any of the defined watched IP addresses.

2. If no valid route exists, the primary line is considered down and unusable.

3. If a valid route exists for at least one of the defined IP addresses and if the route is pointing to an interface other than the backup interface configured for Dialer Watch, the primary link is considered up.

4. If the primary link goes down, Dialer Watch is immediately notified by the routing protocol and the secondary link is brought up.

5. Once the secondary link is up, at the expiration of each idle timeout, the primary link is rechecked.

6. If the primary link remains down, the idle timer is indefinitely reset.

7. If the primary link is up, the secondary backup link is disconnected. Additionally, you can set a disable timer to create a delay for the secondary link to disconnect, after the primary link is reestablished.

the key point is point 2) that states that is not linked to real status of primary link but to missing watched routes at point 1)

also Dialer watch handles topologies where alternate paths different then backup exist per point 3)

Hope to help

Giuseppe

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