[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 Dec 4, 2013, at 7:23 PM, Vlad Yasevich <> wrote:

> On 12/04/2013 11:25 AM, Michael Tuexen wrote:
>> On Dec 4, 2013, at 5:12 PM, Vlad Yasevich <> wrote:
>>> 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
>> That is correct. But I think you should not transfer a private address
>> to another private address belonging to a different network.
>> I don't think this was specified in the older IDs...
>>> 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.
>> Depending on the subnet masks, it might work not not. Are you
>> configuring them with /8?
> No, /16 :). With that, Sys A talking to Sys C will get an abort
> from Sys B when trying to talk to With /8, it'll be
> even worse since SysB and SysC will have duplicate addresses
> within the subnet. :)
> The point is that you don't always know that the same private subnet
> is in reality 2 different subnets with duplicate addresses.
I agree, you can't do it perfectly right. But you can provide some
> I've had to debug an actual production issue similar to this where
> customer had a very similar configuration to above, and their
> associations kept getting aborted. When I tried accessing the
> system that kept sending aborts, I found it was some windows
> server and not a Diameter station they were expecting.
Interesting... Availability of SCTP on Windows is quite limited...
But people seem to use SCTP on Windows.

Best regards
>>> Btw, were there any IDs other then draft-stewart-tsvwg-sctp-ipv4?
>> Yes, one for IPv6.
>> They need to be integrated and improved...
> Ok. I'll take a look.
> Thanks
> -vlad
>> Best regards
>> Michael
>>> Thanks
>>> -vlad
>>>> 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 21:01    [W:0.077 / U:0.448 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site