Subject: Re: Regarding Demultiplexing of BFD Control Packets

From: Dave Katz <[email-masked]>
Date: Sun, 11 Jun 2006 16:49:53 -0700

Not sure if this was ever replied to...

On May 29, 2006, at 10:14 PM, Dr. Soumitra Sinha Roy wrote:

> Sir,
> In draft-ietf-bfd-base-04.txt Sec 6.3 (Page 18), It is
> mentioned that " Once the remote end echoes back the
> local administrator, all further received packets are
> demultiplexed based on the Your duscriminator field
> only(which means that, among other things , the source
> address field can change, or the interface over which
> the packets are recived can change, but the packets
> will still be associated with proper session.)"
>
> Does this mean that Suppose we have two routers RT1
> and RT2.
>
> A session is established between Rt1 and Rt2 at I1
> interface.My Discriminator for RT1 At I1 is X. My
> Discriminator for Rt2 is Y at Interface I1.and session
> state for Rt2 is init.Now, If I send a packet at I2
> interface of RT1 with Your Discriminator as
> Y(My.Discriminator of Rt2 at I1) and My. Discriminator
> = X , then Rt2 will send a BFD Packet with session
> state 3 at Interface I1.

The states and interfaces are immaterial (as is, for that matter, the  
value of My Discriminator, which is free to change.)

The point of the spec is that if a packet is received on any  
interface that has Your Discriminator nonzero, that value is used to  
find the session and the protocol mechanism does whatever it needs to  
do based on the receipt of that packet.

The choice of outgoing interface is highly dependent on the  
scenario;  for the one hop case it is tightly bound, but for the  
multihop case the received packets may arrive on any interface, and  
the outgoing interface choice may be based on routing, for example.

--Dave