Subject: [Tsvwg] SCTP-multihoming association initiation on alternate destination

From: Bhanu Prakash <[email-masked]>
Date: Tue, 05 Dec 2006 15:58:37 +0530

Please clarify the following:

Consider the following setup where in the multihomed HOST-1
is having route to multihomed HOST-2 through a common gateway GW0.
The route to HOST-2 through address a.a.a.a is not reachable.

HOST-1 (address x.x.x.x) -----------   GW0 ------- X ------ HOST-2 
(address a.a.a.a)

HOST-1 (address y.y.y.y) -----------   GW0 ---------------- HOST-2 
(address b.b.b.b)

Here hosts know the destination address through configuration.
Initially the HOST-1 will initiate association with HOST-2 destination
address a.a.a.a (i.e. INIT is sent having src=x.x.x.x and dest=a.a.a.a)
Since the HOST-2 is not reachable through a.a.a.a the timer T1 will
expire at HOST-1.

Now the question is when the HOST-1 should initiate association with HOST-2
alternate destination address b.b.b.b ?

It is whose responsibility to initiate association with alternate 
destination
IP address ? whether the SCTP upper layer or the SCTP stack itself ?

Thanks,
Bhanu.

---

From: Michael Tuexen <[email-masked]>
Date: Tue, 5 Dec 2006 14:11:16 +0100

Hi Bhanu,

the socket-api allows a user at HOST-1 to call sctp_connectx() with
host addresses of HOST-2 and the kernel will use both addresses
to setup the association. One possibility is to send the first INIT
to a.a.a.a and after a timeout retransmit the INIT to b.b.b.b. Or
it could send out both INITs at the same time...

For the one-to-many style API you could use sctp_sendx().

And there are SCTP implementations out there (FreeBSD / Mac OS X)
which support this feature.

Best regards
Michael