On Mar 11, 2011, at 7:44 AM, Will Yu wrote:
I have a query on SCTP standard (RFC 4960). In section 8.2 Path Failure
Detection, it describes the action which end points should take in detecting
When its peer endpoint is multi-homed, an endpoint should keep an
error counter for each of the destination transport addresses of the
Each time the T3-rtx timer expires on any address, or when a
HEARTBEAT sent to an idle address is not acknowledged within an RTO,
the error counter of that destination address will be incremented.
When the value in the error counter exceeds the protocol parameter
’Path.Max.Retrans’ of that destination address, the endpoint should
mark the destination transport address as inactive, and a
notification SHOULD be sent to the upper layer.
In my case, I connected two end points through four IP address. EP1 owns
IP1 and IP2, EP2 owns IP3 and IP4. And IP1 is the primary address for EP1,
while IP3 is the primary address for EP2. There is no other packet in this
association except with Heartbeat and Heartbeat_ACK.
End \ / End
Point1 * Point2
When IP4 is unavailable, the heartbeat messages from IP1 and IP2 with the
destination IP4 cannot received acknowledgement. In this case, PMR in each
EP is set to 4. I observed that EP1 used IP1 and IP2 as source address to
send the heartbeat messages to IP4 respectively. When the heartbeat message
from source address IP2 exceed 4 times, it marked the path(IP2-IP4) is
unreachable. And then IP1 exceed, it would mark the destination IP4 is
unavailable. In my opinion, this result is
There is no state for the path IP2-IP4, only for the remote address IP4.
reasonable with the recognition of IP2-IP4 is a path and IP1-IP4 is
another path for the association. Consequently, the PMR parameter is for
determining which PATH could regard as unavailable.
SCTP supervises remote addresses. So EP1 is supervising IP3 and IP4. So
there is one error counter for IP3
and one for IP4. There is also only a state per remote IP address. So after
the error counter for IP4
exceeds PMR, the IP address IP4 should be marked as unreachable.
But in the section 8.2 Path Failure Detection, the increasing counter
action is based on different destination transport address, not on the
different source-destination address pair. I think it make me confused that
counter will impact the result in my case with the assumption RFC regard the
destination address failure as the critical element for Path Failure
Would you kindly help me clarify the behaviors in Path Failure Detection,
or figure out if I have any misunderstanding in this case?
As said above, SCTP supervises remote addresses, not paths.
PS: It might be better to send SCTP related questions to
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