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sctp multihoming query

Subject: sctp multihoming query
From: Sudhanva Mudigere Narayana Gowda
Date: Fri, 4 Dec 2009 17:27:16 +0530


I have a query regarding sctp multihoming behavior.


I have setup a multihomed association and this is my observation


Host_A (IP a): Local single Homed endpoint


Host_B (IP b(Primary), IP c(secondary)): Remote multiHomed endpoint


During Heartbeat I see that even though the Heart beat req is to the secondary ip of Host_B, the Host_B uses its primary ip as source when sending back the Heartbeat Ack.

Ie  Host_A (IP a) --------HEART_BEAT_REQ-----------> Host_B(IP c)

     Host_A (IP a)<--------- HEART_BEAT_ACK---------- Host_B(IP b)


also during data exchange I observed that even when the data is sent to the secondary ip of Host_B, the SACK is being sent back from the primary ip of Host_B.

  Host_A (IP a) --------DATA_MSG-----------> Host_B(IP c)

  Host_A (IP a)<--------- SACK------------------- Host_B(IP b)


Is this the expected behavior, shouldn’t the node use the same ip on which it received the data or Heart_beat_req on while sending back the responses(Heart_beat_ack or SACK).

Due to this behavior if the primary ip of an endpoint fails the association goes down as the node will not be able to transmit any Heartbeat_Req or Heartbeat_Ack.


On Host_A I blocked the incoming packets which has Host_B(IP b) as source and I expected Host_B to retry using its secondary ip addr, but I observed that even the retries from Host_B uses its primary ip .


Does this mean that an endpoint always uses its primary-ip while sending packets, but might receive packets on primary or secondary-ip?




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