Subject: [Isis-wg] Selectively Ignoring Hello PDU's

From: Saravana Kumar <[email-masked]>
Date: Tue, 10 Sep 2002 17:22:37 +0530

Hi Everyone,

Is there a way for a router(A) to send out Hello PDU's such that they are
processed by only a subset of its neighbors who support a particular new
feature ( restart, for instance) and the rest of its neighbors just ignore
the Hello PDU and do not refresh/re-initialize the adjacency with the
router(A)

One easy way i can think of is to change the value in the protocols
supported TLV to some new value which is recognized only by the routers
supporting the new feature and not by the older generation routers.

Is this feasible (if so, what value of NLPID should be used ?) or is there
any other way in which i can acheive the selective ignoring of hello PDU's.

Thanks,
Sarav

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From: Hannes Gredler <[email-masked]>
Date: Wed, 11 Sep 2002 05:46:28 +0200

On Tue, Sep 10, 2002 at 05:22:37PM +0530, Saravana Kumar wrote:
| Hi Everyone,
| 
| Is there a way for a router(A) to send out Hello PDU's such that they are
| processed by only a subset of its neighbors who support a particular new
| feature ( restart, for instance) and the rest of its neighbors just ignore
| the Hello PDU and do not refresh/re-initialize the adjacency with the
| router(A)
| 
| One easy way i can think of is to change the value in the protocols
| supported TLV to some new value which is recognized only by the routers
| supporting the new feature and not by the older generation routers.
| 
| Is this feasible (if so, what value of NLPID should be used ?) or is there
| any other way in which i can acheive the selective ignoring of hello PDU's.

sarav,

you may want look into the multi-topology draft to see if it fits
your purpose; - squeezing tlv 129 is clearly the wrong place for
your "application";

/hannes

---

From: Saravana Kumar <[email-masked]>
Date: Mon, 16 Sep 2002 14:46:04 +0530

Hannes, Everyone..

First of all, sorry for the late reply, been away from my mail for a while.
Going back to the business at hand, I dont think that the muti-topology
draft is the place to find answers to the requirements for my "application".

Guess i should explain the "application" first and ask questions later. One
of the big challenges for a restarting router is to successfully re-acquire
all its adjacencies without disturbing the area. If any one of the
restarting routers neighbors does not support the restart signalling
feature, then it will re-intializse its adjacency with the restarting router
and flood new LSPs throught the area/domain.

If the restarting router can somehow backup information about its
adjacencies with one of its neighbors, it can later use that information to
re-acquire all its adjacencies without disturbing the network.

So, now when the restarting router comes up, the first step is to retrive
the adjacency information from its neighbor. It doesnt know to which
neighbor it has given the information to, so the restarting router should
send a special hello PDU (with RR bit set) and the neighbor should reply
with a hello PDU (RA bit set) containing the backup information (by
including sub-TLL's in the restart TLV) . All the other neighbor routers
which do not support the restart feature should ignore the hello PDU (so
that they dont reset the adjacency and flood new LSPs through the domain).
The restarting router can now use the adjacency information to generate
hello PDU's on each circuit which are exactly similar to the Hello PDU's
that it generated over the circuit before it restarted.

so, now going back to the original question, how do i ensure that the old
routers which do not support the restart feature would ignore the hello PDU
and not re-initialize the adjacency. Squeezing TLV 129 is one way i can
think of right now. Let me know what problems you foresee in that mechanism
and if there are any alternatives.

Thanks,
Sarav

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From: mike shand <[email-masked]>
Date: Mon, 16 Sep 2002 10:26:25 +0100

How do you plan to ensure that the restarting router can correctly 
synchronize its LSP database with the non-cooperating router?

BTW, I don't think there is a way to make the hello be ignored without a 
protocol change in the non-cooperating router, other than sending it a 
"correct" hello in the first place :-)

         Mike

---

From: Tony Przygienda <[email-masked]>
Date: Mon, 16 Sep 2002 11:12:52 -0700

mike shand wrote:

> BTW, I don't think there is a way to make the hello be ignored without 
> a protocol change in the non-cooperating router, other than sending it 
> a "correct" hello in the first place :-) 

yes, and I would be very reluctant (beside the practical problem that it 
would be impossible practically anyway) to
change the deployed protocol in existing routers.

Meanwhile, all kind of trick can be played and will work in some or most 
circumstances for the restart by storing adjacency
data, it may be however safest to wait for Mike's RFC for an 
interoperable, clean solution.

    thanks

    -- tony

>> > | Is there a way for a router(A) to send out Hello PDU's such that 
>> they
>> are