From: Ben-Shalom, Omer (omer.ben-shalom@xxxxxxxxx)
Date: Sat Dec 22 2001 - 17:37:05 GMT-3
I can give my view on dialer watch here which may not be true not having
worked with dialer watch very intensively
Dialer watch allows you to set a list of networks to be watched (a host is a
/32 network for all intents so 'networks' here is enough).
The networks need to be in the route table for a very simple but powerful
reason - as far as my lab tests went the dialer watch does NOT check the
route table occasionally and triggers if all routes are not there, rather it
is triggered by the withdrawal of a route from the route table !
this means if you want a network that is not in the route table (for example
a network unknown to the router at all) dialer watch will not bring up the
line at all.
Once the network disappears from the table dialer watch checks that none of
the watched networks are there and if they are all gone it will circumvent
the 'interesting traffic' specification IE all traffic is now interesting.
The way to work with dialer watch is:
* Identify a network that indicates the main line is up (or more)
* Set a dialer watch list with those networks, remember the 'broadcast'
keyword if you want
the line to exchange route information later or anything else requiring
broadcasts
* Remember to have a dial map for each of those networks, when a network
disappears and triggers the check if the check fails the map for that
network is used to bring the ISDN line up if it is down, this is very
important !
* Declare the dialer watch on the BRI/Dialer using the list defined
* Set your dialer list to what you want to go through the ISDN when the main
line is UP, normally you would block here things like OSPF hellos and any
other traffic that will keep it up, you can even make all traffic
non-interesting and then the line is down unless the dialer watch kicks in.
When the route goes away all traffic on the ISDN becomes interesting, if the
line is down it will be brought up using the map on the map that went away.
After this the route table is checked periodically every idle timeout to see
if the routes came back from a source DIFFERENT then the ISDN line itself
(we can assume that routes will be relearned through the ISDN line if we
want to maintain connectivity), if so the process is stopped, the
interesting traffic definition from the dialer list is reinstated and so on.
I am not sure if what I described holds for all IOS versions, I did my
checks on 12.1.9
Again - this is to be taken with a grain of salt as I did not do extensive
checks on this, collaborations are welcome.
Cheers.
Omer Ben-Shalom
Senior network analyst
CCIE #8540
Intel GER NMWG.
Disclaimer: The opinions expressed are my own, I am
Not speaking for Intel corp. or representing it in any way.
-----Original Message-----
From: Godwin Pang [mailto:gytpang@jos.com.hk]
Sent: Tue, December 18, 2001 5:53 AM
To: ccielab@groupstudy.com
Subject: Dialer watch question
Hi Group,
Please help me to understand Dialer watch.
Quoted from the document
http://www.cisco.com/warp/public/129/bri-backup-map-watch.html
"When a watched route is deleted, dialer watch checks for at least one valid
route for any of the IP addresses or networks being watched. "
"dialer watch-list group-number ip ip-address address-mask : Defines the IP
addresses or networks to be watched. The address or network (with the
correct mask) that is configured must exist in the routing table. "
I think the first quote said I can backup a particular ip address with
dialer watch, while the second one said the ip address with the mask must be
in the routing table.
However, except loopback interface, I seldom see any ip address (with /32
mask) in the routing table. Is it mean I can only WATCH a loopback address?
Can I WATCH a particular interface?
For example: Imagine there is an isdn link between Router A and Router B
-------------e0-Router_A-S0--------------------------S0-Router_B-e0---------
----------
10.1.1.0/24 11.1.1.0/24
12.1.1.0/24
Can I use dialer watch to WATCH the ethernet interface address of Router B?
e.g. dialer watch-list 1 ip 12.1.1.1 255.255.255.255
Another question
Quoted from the document
http://www.cisco.com/warp/public/123/backup-main.html
"Dialer Watch does not rely on interesting packets to trigger dialing. The
link is automatically brought up when the primary route goes down without
postponing dialing. This is an important consideration on Frame Relay
circuits, where the line protocol may not go down if the DLCI is inactive. "
Assume the connection between Router A and Router B is FR, is it mean that
dialer watch will not dial if the watched network is 11.1.1.0/24 because the
DLCI of Router A is still up even the S0 of Router B is down?
I know the solution is to watch the 12.1.1.0 network, but will it dial if I
WATCH the ip address of router B's S0?
Thanks,
Godwin
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