Hi Samba,
It seems there is firewall between host-X and host-Y, so the cross path packets can not reach the destination?
In my understanding, some aspects may impact the result.
As far as I know, different vendors maybe provide different implementation.
some provide parallel path, like
(px) ----- (py)
A: host-X host-Y
(ax) ----- (ay)
while some provide both parallel and cross path, like
(px) ------ (py)
B: host-X X host-Y
(ax) ------ (ay)
So, if host-Y takes implementation A, I guess the result would not change even you re-configure the network, because host-Y would
not return HBAck in the cross path when it receives the HB message (it doesn't think the cross path is SCTP PATH), I did ever see
such device.
But, the more important point is host-X, it looks very strange.
1. to mark the destination endpoint IPay as NETWORK DOWN on Host-X when it exceeds max retranmission in same path(cross)
consecutively and
If the path of IPax -- IPay is OK, this should not happen, this is the key point.
Host-X would also send HB to IPpy by the source address IPpx, and send HB to IPay by the source address IPax, and the corresponding
HBAck would be returned by host-Y, so num of retransmission would be reset to 0. In the viewpoint of host-X, the right result should
be: parallel paths are both OK and cross paths are both invalid, but the association should be OK.
Do you see the HB message (or DATA chunk) in the parallel path? or host-X only sends HB in the cross path?
By the way, tsvwg@xxxxxxxx is a better list for this discussion.
Regards
Xiangsong
----- Original Message -----
From: "Sambasiva Rao Manchili" <sambasiva.manchili@xxxxxxxxxxxxxxxx>
To: <ietf@xxxxxxxx>
Cc: "Antonio Gambin" <antonio.gambin@xxxxxxxxxxxxxxxx>; "Markus Locher" <markus.locher@xxxxxxxxxxxxxxxx>
Sent: Thursday, April 15, 2010 6:30 PM
Subject: SCTP Mulithoming Communication PATHS Query
Hallo,
I have a query related to SCT Mulithoming communication paths.
Host-X: (IPpx IPax): Multihomed Association with Host-Y (IPpy IPay).
Host-X SCTP Client is running with SCTP stack provided by Vendor X
Host-Y SCTP Server is running with SCTP stack provided by Vendor Y.
Notation.
IPpx means IP Address of Primary path on Host-X
IPax means IP Address of Alternate path on Host-X
IPpy means IP Address of Primary path on Host-Y
IPpy means IP Address of Primary path on Host-Y
Host-X is Communicating as follows :-
-------------------------------------------------------
Primary IP to Primary IP
Host-X(IPpx)--------HBEAT---------->Host-Y(IPpy)
Host-X(IPpx)<-------HBEAT-ACK------Host-Y(IPpy)
Alternate IP to Alternate IP
Host-X(IPax)--------HBEAT---------->Host-Y(IPay)
Host-X(IPax)<-------HBEAT-ACK------Host-Y(IPay)
/*
* Host-X installed in Customer network.
* Customer Network not configured/ not capable to deliver to destination
* in the following two paths. I do not know if they have special requirement
* to configure their network only primary talks to primary and alternate talks
* to alternate, but I see disadvantage in their setup.
* Host-X keeps on trying to reach every Destination received in the
* INIT_ACK message from Host-Y
*
*/
Primary to Alternate Address
Host-X(IPpx)--------HBEAT---------->Host-Y(IPay) (DOES N0T REACH IPay)
Host-X(IPax)--------HBEAT---------->Host-Y(IPpy) (DOES NOT REACH IPpy)
Now Host-X was forced to configured Path Max Retransmissions and Max Init Retransmissions to value of 5, while RTO Initial and RTO
MAX value is set to 1 second.
This results
1. to mark the destination endpoint IPay as NETWORK DOWN on Host-X when it exceeds max retranmission in same path(cross)
consecutively and
2. then sends INIT from IPpx to IPpy and also IPpx to IPay and as soon as it gets the response from any destination(in customer
nework only from IPpy) it is marked as NETWORK UP,
3. but soon or later we receive again NETWORK DOWN and same repeats from step 1.
Now the query is,
Is it right to tell custome Network to re-configure their network to allow
cross communication ?
OR
Is it MUST to change the Host-X stack to stop communicating Cross
i.e., IPpx trying to reach IPay.
Advantage that I see from Host-X Stack :
I also see an advantage with Host-X tranport addresses IPs trying to reach every destination
of the peer. The advantage is If the path between the Host-Y(IPpy) and its next hop is broken and
If the path between Host-X(IPax) and its next hop is broken still Multihoming makes real sense and
could cope up with such breakdown in network while Host-X(IPpx)------->Host-Y(IPay)
If I overlook any other disadvantage of Host-X stack, please correct me.
Looking forward for your suggestion from your expert knowledge. If something not clear please feel to ask me.
Thanks in advance.
Thanks,
samba.
Sambasiva Rao Manchili
Software Development Engineer
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Network and Service Investigation
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