OSPF and SPF Algorithm

OSPF and SPF Algorithm
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Subject Author Date
OSPF and SPF Algorithm CiscoKid 04-26-2005
Posted by CiscoKid on April 26, 2005, 2:14 am
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I have been unable to find an answer for this question...when OSPF runs the
SPF algorithm, is the routing table wiped and started from scratch or is it
just updated with changes? Most of what I've found would suggest it is
started over from scratch, but nothing I've read really says for sure.

Thanks in advance,

Mikey


home networking made easy, greater protection, less stress, introducing nm 5.0, 728x90
Posted by John Agosta on April 25, 2005, 9:37 pm
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Look at the timers in the route table.

Purposely cause a route to fail and grab another route.

Compare the timer for the molested route with the rest of the entries in the
route table.

If all the timers are the same, I suspect the table is startet from scratch.
If they are not, then I suspect just the new (molested) route was re-set as
far as 'show ip route' is concerened.....


I suspect the actual answer is "implementation"

Interesting question by the way. Good for the "routing" category in
Jeapardy.


-ja







> I have been unable to find an answer for this question...when OSPF runs
the
> SPF algorithm, is the routing table wiped and started from scratch or is
it
> just updated with changes? Most of what I've found would suggest it is
> started over from scratch, but nothing I've read really says for sure.
>
> Thanks in advance,
>
> Mikey




Posted by _PepeR_ on April 26, 2005, 12:38 pm
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CiscoKid napisał(a):
> I have been unable to find an answer for this question...when OSPF runs the
> SPF algorithm, is the routing table wiped and started from scratch or is it
> just updated with changes? Most of what I've found would suggest it is
> started over from scratch, but nothing I've read really says for sure.
>

Hi,
You have right. If there is a change in network topology first the
topology database is updated, then SPF algorithm generate new routing
table. Old routing table is replaced with new when SPF finish building
new routing table and hold timer expires. It is described in CCNP
curriculum, chapter 6.2.6.

Peter,

--
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Piotr '_PepeR_' Wojciechowski | "The trouble with being a god is that
NetAdmin @mlekomat.com.pl | you've got no one to pray to"
http://peper.eu.org GG: 484520 | -- (Terry Pratchett, Small Gods)
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