[lkml]   [2013]   [Dec]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: Supporting 4 way connections in LKSCTP
On 12/04/2013 11:01 AM, Michael Tuexen wrote:
> On Dec 4, 2013, at 4:41 PM, Vlad Yasevich <> wrote:
>> On 12/04/2013 09:50 AM, David Laight wrote:
>>>>> In normal operation, IP-A sends INIT to IP-X, IP-X returns INIT_ACK to
>>>>> IP-A. IP-A then sends HB to IP-X, IP-X then returns HB_ACK to IP-A. In
>>>>> the meantime, IP-B sends HB to IP-Y and IPY returns HB_ACK.
>>>>> In case of the path between IP-A and IP-X is broken, IP-B sends INIT
>>>>> to IP-X, NODE-B uses IP-Y to return INIT_ACK to IP-B. Then IP-B sends
>>>>> HB to IP-X, and IP-Y returns HB_ACK to IP-B. In the meantime, the HB
>>>>> communication between IP-B and IP-Y follows the normal flow.
>>>>> Can I confirm, is it really valid?
>>>> As long as NODE-B knows about both IP-A and IP-B, and NODE-A knows about
>>>> both IP-X and IP-Y (meaning all the addresses were exchanged inside INIT
>>>> and INIT-ACK), then this situation is perfectly valid. In fact, this
>>>> has been tested an multiple interops.
>>> There are some network configurations that do cause problems.
>>> Consider 4 systems with 3 LAN segments:
>>> A) on LAN X and on LAN Y.
>>> B) on LAN X and on LAN Y.
>>> C) on LAN X.
>>> D) on LAN X and on LAN Z.
>>> There are no routers between the networks (and none of the systems
>>> are running IP forwarding).
>>> If A connects to B everything is fine - traffic can use either LAN.
>>> Connections from A to C are problematic if C tries to send anything
>>> (except a HB) to before receiving a HB response.
>>> One of the SCTP stacks we've used did send messages to an
>>> inappropriate address, but I've forgotten which one.
>> I guess that would be problematic if A can not receive traffic for
>> on the interface connected to LAN X. I shouldn't
>> technically be a problem for C as it should mark the path to
>> as down. For A, as long as it doesn't decide to ABORT the association,
>> it shouldn't be a problem either. It would be interesting to know more
>> about what problems you've observed.
>>> Connections between A and D fail unless the HB errors A receives
>>> for are ignored.
>> Yes, this configuration is very error prone, especially if system B and
>> system D are up at the same time. Any attempts by system A to use
>> LAN Y will result in an ABORT generated by system B. I have seen
>> this issue well in production and we had to renumber system D to solve
>> it.
> The point is that address scoping should be used. When sending an
> INIT from to you should not list,
> since you are transmitting an address to a node which might or might
> not "be in the same scope". We had IDs for that in the past, but
> they never made it to RFC state, because they were not progressed enough
> by the authors. Maybe we should push them again...

But these 2 are technically in the same scope. They are both private
address types. Also, this will not solve the problem either since
the configured addresses could be:
System A) on Lan X, on Lan Y
System B) on Lan X, on Lan Y
System C) on Lan X, on Lan Z

Same problem will occur.

Btw, were there any IDs other then draft-stewart-tsvwg-sctp-ipv4?


> Best regards
> Michael
>> -vlad
>>> Of course the application could explicitly bind to only the 10.x address
>>> but that requires the application know the exact network topology
>>> and may be difficult for incoming calls.
>>> David
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-sctp" in
>> the body of a message to
>> More majordomo info at

 \ /
  Last update: 2013-12-04 17:21    [W:0.098 / U:0.320 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site