Subject: Re: draft-vasseur-mpls-ospf-pcsd-discovery-00.txt

From: "Manral, Vishwas" <[email-masked]>
Date: Thu, 8 Aug 2002 13:42:37 -0400

Hi Venkata,

>  I don't *fully* support to make PCS server an ASBR.
>  IMO, we are overloading the functionality of ASBR.
We are just using an already existing functionality for a very similar
function. We have done this for a lot of other purposes and I feel it is
valid.

>  The way draft is right now is fine (as explained by Peter).
>  Make reachability of the PCS server outside the scope
>  of the document.
Well that is good enough.

However its easy in OSPF to figure out whether a router is down or not.
Incase we go the way the draft is, the PC client would only know of a PC
Server not existing/going down after few failed retries or when the MaxAge
of the LSA expires. So the fact becomes that an advertized PCS may not be up
at all, its just that we have the IP address and capabilities of all PCS,
which would not make it so very dynamic(as I see it).

>  The current OSPF-TE draft also does the same for Router
>  Address (which is required to be routable always and
>  very different from OSPF Router ID)
>
>   The Router Address TLV specifies a stable IP address of the
>   advertising router that is always reachable if there is any
>   connectivity to it.

When a link goes down the adjacent router will not advertize the link and
hence the link and the router reachable thru the link will not be used for
TE purposes either. We do not do a best effort in TE, where we actually try
and only in case of failure realize a router/link could be down.

I guess some implementations do use the router LSA to figure out if the
router is actually reachable. The router LSA is updated when the link goes
down, and when that happens we canot reach the router and we do not use the
TE information of that router either.

>  Vishwas, how is this different from normal prefix reachability
>  when ABR is aggregating prefixes ? As we know, with aggregation
>  we lose some information.
It is not, and that is what I am trying to state. Even the existence of a
route to a prefix may not mean the PCS is up.

>  In other words, if an internal router gets disconnected in an
>  aggregated area, How are other area routers know about the
>  fact ?
Well if the router is an ASBR, other area routers know of the router because
type-4 LSA's for the router. If a router route for the router exists the
router is reachable when it is not, it is not.

Hope I am clearer this time.

Thanks,
Vishwas