From: Kenneth Wygand (KWygand@customonline.com)
Date: Mon Jul 05 2004 - 18:57:40 GMT-3
Tim,
There are a total of three timers associated with Dialer Watch:
1) Idle-timeout - this is how often the routing table is checked to see if the watched route has returned to the IP routing table. Essentially this checks to see what next-hop interfaces are available to the watched route and if there is a route available using an alternate interface, it will trigger a disconnect request for the ISDN circuit. This is not an immediate disconnect, rather a request that must still pass through the "dialer watch-disable" command. It should also be noted that an "alternate interface" should be understood as any interface other than the one on which the dialer-watch feature is configured.
2) dialer watch-disable - this is how long the ISDN circuit should stay active after receiving a disconnect request due to reachability to the watched route into the IP routing table. Note that this timer will only start after receiving notification that the primary route has returned, which is only checked at expiration of the idle-timeout.
3) dialer watch connect delay (12.2(8)T) - this is how long the router will wait to dial the backup circuit once the watched route has been removed from the IP routing table. At the end of this timer, the IP routing table is checked again to see if the route has returned. If not, the backup interface is kicked in and the idle-timeout starts.
Your question pertains to the new "dialer watch connect delay" command. If this command is not configured, the ISDN circuit is dialed immediately after the watched routes are removed from the IP routing table. This command allows routing protocols to converge to determine if your IGP can find an alternate route to the watched network.
The following are the sequence of events as per the Doc CD:
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.
Note that step 4 indicates that the ISDN circuit is immediately brought up when the watched route disappears. Of course, since this is 12.2 documentation, it doesn't account for the "dialer watch connect delay" command (http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft/122t/122t8/ftdialwl.htm)
Now I will answer your other direct questions inline:
In addition, once the dialer watch has triggered a call, I know that dialer
watch checks the route table everytime the dialer idle-timeout expires.
But, what about before dialer watch has triggered a call? How often does
dialer watch check the route table in this case?
***Immediately, see description above.
I assume that the dialer idle-timeout timer isn't active before isdn has an
active call. Is this true?
***True
Here's the problem.
Let's say I want dialer watch to trigger a call in the shortest amount of time
possible.
Depending the routing protocol being used, what is the shortest amount of
time?
***Immediately, this is default without using the "dialer watch connect delay" command.
Hope this helps!
Ken
________________________________
From: nobody@groupstudy.com on behalf of ccie2be
Sent: Mon 7/5/2004 4:55 PM
To: Group Study
Subject: Dialer Watch
Hi guys,
Assume dialer watch is configured to trigger an isdn call if the primary
connection goes down.
It seems to me that there are 2 time intervals that determine how long after
the primary connection goes down dialer watch kicks in:
a) how often dialer watch checks the route table for the watched route and
b) how long after the primary connection goes down before a route learned via
the primary connection is removed from the route table.
So far, does everyone agree with this?
In addition, once the dialer watch has triggered a call, I know that dialer
watch checks the route table everytime the dialer idle-timeout expires.
But, what about before dialer watch has triggered a call? How often does
dialer watch check the route table in this case?
I assume that the dialer idle-timeout timer isn't active before isdn has an
active call. Is this true?
Here's the problem.
Let's say I want dialer watch to trigger a call in the shortest amount of time
possible.
Depending the routing protocol being used, what is the shortest amount of
time?
Thanks, Tim
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