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SubjectRe: Supporting 4 way connections in LKSCTP
On 12/04/2013 12:57 PM, Sun Paul wrote:
> As I know, the A to C and A to D case must have a router in between to form
> SCTP multihome topology.

Not necessary. I've produced proper multihoming topologies with just
VLANs and different subnet assignment. You can even remove VLANs
if you correctly set your arp_ignore and arp_announce values.


> On Dec 4, 2013 10:51 PM, "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.
>> Connections between A and D fail unless the HB errors A receives
>> for are ignored.
>> 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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