The MPLS-OPS Archive

[Spice Sylvia <falsesylvia@yahoo.co.uk>]

Hi,

 

A couple of questions as to what is arousing my curiosity:

 

a. the "map" could be wrong/outdated etc etc?

b. the chances that the map is wrong is as likely as the suggestions given on the way were wrong [may not be today as maps are a better "industry" than suggestions :)] but in a theoratical sense, that analogy would hold true.

c. I am not saying "RIP". All I am asking is if there are other solutions to the Bellman Ford problem?

 

By the logic of eBGP and/or RIP, one could simply do something like this:

 

"make all your networks as trees"

 

As in , no loops/feedback/closed graphs. if there is a secondary link, treat it as backup. In that case, bellman ford solutions do not need unique identifiers, or CTI, do u agree?

 

R1------R2-------R3----------R4--------R5-------R6

 

we could have branches coming out from each R1 to R6 and still the node Ids would have local signifinace (for example in the above R1 could be the same as R4 etc if they were all RIP peers and I could do away with CTI in the above topology).

 

The 1st thing that comes to my mind when one sees closed graphs/rings is feedback systems theory.

What was wrong in designing networks as "trees" and not as "rings" and simply using the alternate paths as backups? That would serve the purpose too, would it not?

 

-Sylvia

 

M. ELK" <elkou141061@hotmail.com> wrote:

> Spice
>
> Small story :
>
> In 1990 , went to London for training on certain IP BOX .
> At that time the debate between distance-vector (RIP) and SPF (mainly at 
> this time it was
> OSPF , IS-IS was not in the picture) was not yet setlled down .
>
> The training was outside LON so we hired a car to visit central London , 
> with some
> direction from the hotel we started the journey . and stopped for direction 
> along the way .
> we found that we are going in circle (loop) , finally we reached .
>
> Next trip , we got a map and followed the sign (road block ..etc ) and we 
> reached central
> London very smoothly .
>
> at that time the above case ,triggered an analogy in my mind between the 
> above and RIP versus OSPF .
>
> What was wrong with RIP ? simply we stopped for direction and take the 
> suggestion
> as faithvalue ie: we fully tru!
>  sted the
>  suggestion (we have no other choice) 
> . some
> of those suggestion was bad and hence we got in a circle .
>
>
> The book "rounting in the internet ,by Huitema" discussed the RIP behaviour 
> in details ,
> despite all the trick (poisoning ,reverse poisoing ,hold time ..etc ) still 
> in certain topology
> only the count to infinity could sort the pblm .
>
> my guess that the pblm could be sorted out if the recieving node could judge 
> if the advertisement recieved from neighbor is good or bad . this imply :
> 1) The advertisement packet carry info which could be checked for validity .
> 2) the recieving node have some algorithm to check those info and return
> "Good" or "Bad" .
>
> the simplest sort of this info is the "path vector" , the recieving node 
> could check
> if any loop very easily .
>
> but now it is no longer rip ,it is something like running eBGP (without 
> policy , cost is the path count ie: the nbr of AS in the path . ) betwee!
>  n 
> all
>  nodes and consider each node an AS .
>
> As Eric indicated , RIP is dead/gone . The requirement of provider is now 
> very high that even
> fast convergence of IS-IS/OSPF ( 1-2 sec) is not enough/adequate . The 
> provider
> requirement is now 50-100 msec . Their is many paper for msec convergence 
> for SPF IGP
> by decreasing the timer , eleminate to run full SPF ..etc ( Toward msec IGP 
> convergence ,
> draft-alaettingolu-isis-convergence-00 ,Nov 2000 ) .
> The point is not just if RIP could be changed to eliminate possible loop 
> creation but what is
> the convergence time . If RIP could be changed to provide msec convergence 
> ,the provider's
> will be ready to listen .
>
> Brgds
>
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