Re: Supporting 4 way connections in LKSCTP

[Michael Tuexen]

On Dec 4, 2013, at 5:12 PM, Vlad Yasevich <vyasevich@xxxxxxxxx> wrote:

> On 12/04/2013 11:01 AM, Michael Tuexen wrote:
>> On Dec 4, 2013, at 4:41 PM, Vlad Yasevich <vyasevich@xxxxxxxxx> 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) 10.10.10.1 on LAN X and 192.168.1.1 on LAN Y.
>>>> B) 10.10.10.2 on LAN X and 192.168.1.2 on LAN Y.
>>>> C) 10.10.10.3 on LAN X.
>>>> D) 10.10.10.4 on LAN X and 192.168.1.2 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 192.168.1.1 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
>>> 192.168.1.1 on the interface connected to LAN X.  I shouldn't
>>> technically be a problem for C as it should mark the path to 192.168.1.1
>>> 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 192.168.1.2 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 10.10.10.1 to 10.10.10.4 you should not list 192.168.1.1,
>> 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) 10.0.0.1 on Lan X, 10.10.0.1 on Lan Y
> System B) 10.0.0.2 on Lan X, 10.10.0.2 on Lan Y
> System C) 10.0.0.3 on Lan X, 10.10.0.2 on Lan Z
> 
> Same problem will occur.
Depending on the subnet masks, it might work not not. Are you
configuring them with /8? 
> 
> Btw, were there any IDs other then draft-stewart-tsvwg-sctp-ipv4?
Yes, one for IPv6.
http://tools.ietf.org/html/draft-stewart-tsvwg-sctpipv6-01
They need to be integrated and improved...

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
>>>> 
>>> 
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>> 
> 
> 

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