From: CCIE FUN (ccieexam2002@xxxxxxxxx)
Date: Tue Aug 13 2002 - 15:48:34 GMT-3
Snapshot routing has nothing to do with Classful and
classless protocols.
It is used with Distance vector protocols.
except EIGRP is an exception, it is advance distance
vector protocol. You cannot use it with Snapshot
because EIGRP relies on hello's and it will defeat the
whole purpose of the snapshot routing.
Basically what snapshot routing means is that the
client router dials into the server router and takes a
quick snapshot of the routing table, updates it's own
routing table and then disconnects after a
administrator defined time.
Whereas it can't be used with Link-state protocols
because, these protocols rely on Hello's and if the
hello's are allowed then the link will be UP
constantly.
Demand circuit is exclusively used with OSPF, OSPF
uses the concept of LSA's, all the OSPF LSA's have
MAXAGE of 30 minutes, this means that the LSA's
refresh every 30 minutes, SO if you do not have demand
circuit configured, the ISDN link will come up every
30 minutes for a LSA refresh.
Demand circuit was based around the IDEA of not
allowing the LSA's to ageout. This means the LSA's are
never refreshed and the link does not come up because
of that.
if you type a command
"sh ip ospf database"
you will see the LSA's for the ISDN with a DNA ( do
not age) tag under the AGE column
On the Demand circuit the OSPF hellos are also
suppressed and link stays down unless there is an
topology change.
Hope that helps.
--- Raj <raj.bahad@totalise.co.uk> wrote:
> Also, Snapshot routing is only useful when you are
> running classful
> protocols (RIP, IGRP, IPX-RIP). If you have EIGRP
> running with masks that do
> not fall on their natural boundary with respect to
> its IP address, you will
> be missing a lot of your VLSM'd routes.
>
> Raj.
>
> -----Original Message-----
> From: nobody@groupstudy.com
> [mailto:nobody@groupstudy.com]On Behalf Of
> Colin Barber
> Sent: 13 August 2002 08:50
> To: 'ccielab@groupstudy.com'
> Subject: RE: snapshot vs demand circuit
>
>
> Snapshot routing is designed for distance-vector
> routing protocols. Demand
> circuit is part of the OSPF specification and
> therefore can only be used for
> OSPF.
>
> Snapshot routing only synchronises after a preset
> time interval. Demand
> circuit will synchronise as soon as a topology
> change occurs.
>
> Colin.
>
> -----Original Message-----
> From: Jeff Tukovinit
> [mailto:tukovijj@global.t-bird.edu]
> Sent: 10 August 2002 22:58
> To: ccielab@groupstudy.com
> Subject: snapshot vs demand circuit
>
>
> Folks,
> This is probably an easy questions for many of you
> but I can't understand
> the difference between snapshot and demand circuit.
> What are advantages and
> disadvantages of each one. Thanks!
>
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