Hi Lili,
Your proposed change assumes that the non-DR router knows when the
DR has finished sending LS request packets. I am not sure this can
be assumed, since a router doesn't indicate when it is finished
sending LS request packets (and might not send any).
I think the only indication is when the DR declares the adjacency
to be Full when the LoadingDone event occurs (and adds the neighbor
to its LSA).
Even if the non-DR router determines via Database Description
packets that the DR has out-of-date LSAs, the DR could receive
those LSAs from another router.
It seems easier to just require that the DR's LSA include a link to
the router itself (router i in my example), or to the other non-DR
router j (which is what I used in my draft), before router i includes
a link to j in its router-LSA. I prefer the latter because then
router i advertises a link to j only if router i is Full with the DR
and the DR is Full with router j. Thus, by transitivity router i is
equivalent to being Full with router j (i.e., router i is as
up-to-date as router j).
Richard
Lili Wang wrote:
Hi Richard,
Sorry for the late reply!
Yes, this is a problem with the current spec. We incorrectly convinced
ourselves that such a check is not required.
Here's the proposed change.
We make sure the non-DR router have a synchronized database with the DR before
advertising the Type 1 link to other non-DR router.
We declare the DR as a fully synchronized adjacency after having all the DR's LSA request satisfied (i.e., Our LSA update for the LSA requests are acknowledged by the DR.) in addition to having a full adjacency with the DR.
The rule then will look like the following:
o If a router is not the DR and has a fully synchronized adjacency to the DR,
it MUST add a Type 1 link corresponding to each neighbor that is in
state 2-Way or higher.
Tanks,
Lili
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Richard
Ogier
Sent: Tuesday, May 17, 2011 12:05 PM
To: [email protected]
Subject: Re: [OSPF] OSPF Hybrid Broadcast and P2MP Interface Type
Section 3.6 of draft-nsheth-ospf-hybrid-bcast-and-p2mp-01
has the following rule:
o If a router is not the DR and has a full adjacency to the DR, it
MUST add a Type 1 link corresponding to each neighbor that is in
state 2-Way or higher.
Suppose i and j are non-DR routers. It seems to me that i should
also require that the DR's router-LSA include a link to j before
i adds a Type 1 link corresponding to j, in order to ensure that
i and j are fully synchronized before either uses the other as
a next hop. Is there a reason why this condition was omitted?
To explain further, the SPT calculation (Section 16.1 of RFC 2328)
requires that router j advertise a link back to router i before i
can use j as a next hop (and vice versa). Thus, routers i and j can use
each other as a next hop if they both advertise a link to each other.
Therefore, the above rule from draft-nsheth only ensures that
routers i and j are fully adjacent with the DR before either can
use the other as a next hop. As a result, the DR might not be fully
adjacent with router i or j, and thus i and j may not be fully
synchronized. Note that full adjacency with a neighbor does not
imply that the link state databases are synchronized (see footnote 23
in RFC 2328). It only means that the router is at least as
up-to-date as the neighbor, since it only means that all Link
State Requests have been satisfied.
Please correct me if I am mistaken.
Richard
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