Sure I will add that in the text.
From: Mike Shand
Date: Tuesday, October 6, 2015 at 12:41 AM
To: Pushpasis Sarkar
Cc: "Stewart Bryant (stbryant)", 'Jon Hudson',
"[email protected]<mailto:[email protected]>"
Subject: Re: Routing directorate QA review for
draft-ietf-rtgwg-rlfa-node-protection
Ah! OK, I hadn't read this when I replied:-)
Still it would help if the fact that all cost are equal were stated.
Mike
On 05/10/2015 18:56, Pushpasis Sarkar wrote:
Hi Mike,
My apologies.. I take back the comment below… SPT rooted on N does NOT have
S-E link for paths to E and D1.. Sorry for the confusion once again…
I will see if I can come with any example where E and D1 can be excluded from
PQ-space… If not I will modify the text to include E and D1 as well…
Regards,
-Pushpasis
From: rtgwg on behalf of Pushpasis Sarkar
Date: Monday, October 5, 2015 at 9:56 PM
To: Mike Shand
Cc: "Stewart Bryant (stbryant)", 'Jon Hudson',
"[email protected]<mailto:[email protected]>"
Subject: Re: Routing directorate QA review for
draft-ietf-rtgwg-rlfa-node-protection
Hi Mike,
I forgot to mention.. Even if we follow the below definition of Extended
P-Space from section 2 and 5.1.1.2 in RFC7490…
“Extended P-space:
Consider the set of neighbors of a router protecting a link.
Exclude from that set of routers the router reachable over the
protected link. The extended P-space of the protecting router
with respect to the protected link is the union of the P-spaces of
the neighbors in that set of neighbors with respect to the
protected link (see Section 5.2.1.2).
“
And
“The description in Section 5.2.1.1 calculated router S's P-space
rooted at S itself. However, since router S will only use a repair
path when it has detected the failure of the link S-E, the initial
hop of the repair path need not be subject to S's normal forwarding
decision process. Thus, the concept of extended P-space is
introduced. Router S's extended P-space is the union of the P-spaces
of each of S's neighbors (N). This may be calculated by computing an
SPT at each of S's neighbors (excluding E) and excising the subtree
reached via the path N->S->E. Note this will excise those routers
that are reachable through all ECMPs that include link S-E. The use
of extended P-space may allow router S to reach potential repair
tunnel endpoints that were otherwise unreachable. In cost terms, a
router (P) is in extended P-space if the shortest path cost N->P is
strictly less than the shortest path cost N->S->E->P. In other
words, once the packet is forced to N by S, it is a lower cost for it
to continue on to P by any path except one that takes it back to S
and then across the S->E link.
"
So if we apply the above definitions in the diagram below from the current
draft…
D1
/
S-x-E
/ / \
N---+ R3--D2
\ /
R1---R2
Then Ext-P-Space of S w.r.t S-E link cannot include E and D1 as SPT rooted at N
has ECMPs paths traversing the S-E link for destinations E and D1. Basically if
S forces a packet destined for E or D1 to N, N can send it back over the path
N->S-E. So once again E and D1 cannot be in PQ-space of S wrt S-E link.
Hope this resolves your comment :)
Thanks
-Pushpasis
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