From: kasturi cisco (kasturi_cisco@xxxxxxxxxxx)
Date: Thu Jul 25 2002 - 15:47:39 GMT-3
Carlos,
This is what i have undertsood as -
When the scenario asks for a backup option there are 3 of them if its ISDN
(assuming ISDN)
1. Backup interface command
2. Floating static routes
3. Dialer Watch
-----------
If u are allowed "backup option" then use 1.
- But the downside is it cant monitor end-end connectivity (like FR PVC on
Multipoint FR link),also if u are required to keep the BRI usable then this
is not the option. Go to 2.
2. U may are may not be allowed Floating static routes..of course advantage
is they are protocol independent.Here u need to ensure that the link is not
kept up by the Hellos/broadcasts if the backup link comes up when using the
static route (if used)
3.If lets say 1/2 are not allowed u can use Dialer watch. When u use dialer
watch u need to ensure that the routing protcol does not keep the link up
thru hellos/broadcasts otherwise the idle-timer does not expire and hence
the Primary link wont be used effectively. To prevent this it depends on the
protocol on the ISDN link which can be -
say DV protcols ..use can use snapshot routing or deny ip any any
say EIGRP ..deny EIGRP any any
say OSPF...use IP ospf demand ckt or deny ospf any any.
Am i correct ? someone correct me if i am wrong.
HTH.
kasturi.
>From: "Carlos A. Silva" <carlos@mnet.com.mx>
>Reply-To: "Carlos A. Silva" <carlos@mnet.com.mx>
>To: "Ccielab" <ccielab@groupstudy.com>
>Subject: [ospf demand vs. dialer-watch] when to use either
>Date: Thu, 25 Jul 2002 10:58:15 -0700
>
>hi, all:
>
>right now i'm studying isdn for the exam and came across a scenario that
>could be solved by using either.
>the choice of using ospf-demand or dialer-watch is something that's not
>that
>clear to me right now and will depend on whatever
>we get asked during the exam. i was wondering if anyone out there could
>offer some assistance to figure out what would be
>the better choice when asked to deploy a solution that could (apparently)
>be
>solved with either method.
>
>as far as i can tell the only difference is that ospf-demand would come up
>whenever there's any change in the ospf
>database and dialer-watch only when a (set of) route(s) gets lost. with
>ospf-demand the ckt will go down as soon as the
>database is updates (and there's no interesting traffic) while dialer-watch
>will go down for brief periods of time, then check,
>see that the lost route is still down and bring up the bri (you could say
>bri will stay up as long as the route is lost).
>
>now, please bear in mind that i understand that these 2 features are not
>the
>same (functionally), but they could be used
>to accomplish 'almost' the same thing in the exact same scenario.
>
>thoughts?
>
>regards,
>carlos.
>
>Carlos A. Silva [tel]: 52.818.401.2191
>Micronet de Mixico http://mnet.com.mx
>
>"...sal del camino, toma la ruta..." - Cerati
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