Subject: question on microloops

From: "Alok" <[email-masked]>
Date: Sun, 31 Jul 2005 23:51:02 +0530

Hi,

With regard to:
http://www.ietf.org/internet-drafts/draft-ietf-rtgwg-microloop-analysis-00.txt

If the head end "signals" the path to the "tail end",
a. how can loops be formed?
b. Would the path setup given in the example (link A-C) not fail?

Well ofcourse I know the draft does not make an assumption that paths are
explicitly setup, but just curious....
============================================

The only other question I have from the thread that I have been following is
a comment from Russ White:

" I understand the difference if these are your actual definitions (though
they need to be clarified in the doc), but I don't see how you can tell
the difference between the two. Either a neighbor's path is loop free,
which means their metric is lower than yours--and in that case, they
won't be using you as their next hop. Or, you don't know if it's loop
free or not, because your neigbor is using you as their next hop. "

My question:
What do you do incase there are negative "edges/arcs" in the graph/the
metrics associated with a prefix is lowered?

-thanks
Alok

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---

From: Curtis Villamizar <[email-masked]>
Date: Sun, 31 Jul 2005 23:24:40 -0400

In message <[email-masked]>
Alia Atlas writes:
>  
> Hi Alok,
>  
> On 7/31/05, Alok <[email-masked]> wrote:
> > Hi,
> > 
> > With regard to:
> The question is where does the head-end get the traffic.  For RSVP-TE
> LSPs, the make-before-break mechanism ensures that micro-loops don't
> form along the LSP.  However, it is still possible for them to form
> between separate LSPs.

In a network running RSVP/TE if properly configured (not a partial TE
mesh) there is no possibility of forming loops unless traffic falls
back to IP.

For example, if there is a full mesh of RSVP/TE tunnels within a given
IGP area, no RSVP/TE loops can formed within the area.  It is
perfectly reasonable to do this with IGP areas of about 100 routers.
Right now it seems that about 400 routers per area would be pushing
the limit.

With multiple areas running RSVP/TE microloops are only possible to
the extent that they a loop crossing multiple areas is at least
theoretically possible.  A multiarea IGP microloops seems highly
unlikely.  If hierarchical RSVP/TE is used such that there is scalable
edge to edge TE then even these highly unlikely multiarea microloops
are not possible.  btw- I don't know anyone that is doing hierarchical
RSVP/TE to get edge to edge TE.

Curtis