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+1 vote

I've got a question about primary SCTP addresses, what it exactly means to be primary.

Consider an association with two addresses (ie. two sockaddr:s were supplied to sctp_connectx()). SCTP starts using the primary path, then after a while the connection goes down. SCTP tries the secondary path, which is functional. After a while the primary path becomes operational again.

Now, as far as we've seen the SCTP stack delivers a SCTP_ADDR_AVAILABLE event, but doesn't revert back to the primary path, which would be desirable to us. We've discovered the SCTP_PRIMARY_ADDR socket option, but looking at the kernel sources the zeroth address specified with sctp_connectx()
is always made the primary one, so there would be no benefit in trying to reinforce the primaryness with SCTP_PRIMARY_ADDR on SCTP_ADDR_AVAILABLE.

In summary, I'd like to know how to tell the SCTP stack to prefer the zeroth address of sctp_connectx() to transmit data whenever its path is available?

posted Jul 12, 2013 by anonymous

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1 Answer

+1 vote

All primary addr means is that for as long as that address exists as an active association, it will be the source address used when routing packets to a destination. And yes, the primary address might change over the life of a connection.

I don't understand your concern though. you've found the SCTP_PRIMARY_ADDR socket option, how come you can't issue a setsockopt call in response to the reception of a ADDR_AVAILABLE event (or any other address changing event)?

answer Jul 12, 2013 by anonymous
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0 votes

We are using LKSCTP version 1.0.16 and have configured the SCTP configuration parameters as follows:

SctpInitMaxAttempts : 10
SctpInitRTO : 3000
SctpMinRTO : 1000
SctpMaxRTO : 60000

We observed that SCTP:INIT re-transmission is occurring at interval 6,12,24.., 6,12,24.., 6,12,24....... As per our understanding re-transmission should occur at interval 3,6,12,24..., 3,6,12,24...3,6,12,24... since SctpInitRTO=3000.

Could you please let us know if it is an expected behavior or not. Also why re-transmission interval is not started with 3,6,12,24...

+2 votes

Is LKSCTP 100% compliant with the following?

RFC 2960 - SCTP (obsoleted by RFC 4960)
RFC 3309 - SCTP Checksum Change (obsoleted by RFC 4960)
RFC 3758 - SCTP Partial Reliability Extension
RFC 4460 - SCTP Errata and Issues
RFC 4895 - Authenticated Chunks for SCTP
RFC 4960 - SCTP
RFC 5061 - SCTP Dynamic Address Reconfiguration
RFC 5062 - Security Attacks Against SCTP

Any pointers are welcome?

+4 votes

Are the values in /proc/sys/net/sctp/sctp_[rw]mem honored? Or are they overridden by those in /proc/sys/net/core/[rw]mem_*

Furthermore, the kernel documentation states that sctp_wmem has no effect, but makes no such mention for sctp_mem and sctp_rmem.