On Apr 30, 2011, at 12:15 PM, Schoch Christian wrote:
On Apr 30, 2011, at 9:11 AM, Schoch Christian wrote:
During a measurement with CMT-SCTP and PF i figured out, that
sometimes a ICMP Destination unreachable message triggers a
message transmission on an inactive data path that has been
primary before.
It looks as the ICMP message is reseting the inactive state back
to active without reseting RTO.
This behavior is triggered by a returning heartbeat message when
no ICMP unreachable by data is sent quite before.
Test system are two multi-homed hosts with FreeBSD8.1 and a WANem
host between.
A wireshark log can be provided on demand (quite large).
Hi Christian,
any chance to upgrade the FreeBSD machines to head or to use newer
SCTP sources, which I could provide? It would require a recompilation
of the kernel...
It is possible, but the results could be provided not until next week
if a reboot is necessary.
I can use any sources you could provide me since nothing else is
done at this systems.
OK, but maybe I can try to understand what is going on.
How many paths do you have? One is inactive, but was primary, so it
is confirmed. On another one, you get an ICMP (which one? Port unreachable,
host unreachable, ...). Do you have more than two paths?
Setup looks like this:
-------- ----cut---
Host A WANem Host B
-------- ----------
Transfer is running on both path from A to B till the primary link is
cut between WANem and the receiver and the whole transfer switches to
the second path. The ICMP message (Host not reachable with a Heartbeat
as attachment) is received on the primary interface from WANem host.
As I tested this morning, the primary path is switching to unreachable
due to the ICMP message but should be in this state quite before by
exceeding path.max_retrans.
So this ICMP message does two things:
- Set the primary path to unreachable
- Triggers something to retry data transfer on the primary path.
The ICMP message would not reset the RTO, since you need an ACKed TSN
or a HB-ACK to to that. Since it is inactive, it is missing these.
Sending on an inactive path is OK, as soon as you enter the dormant
state, which means all your paths are inactive.
Transfer is still running on second link which is active.
Are you using the PF support for CMT?
Yes, but without NR-SACK and DAC.
I uploaded the pcap file to:
http://37116.vs.webtropia.com/cmt_2.pcap
Best regards,
Christian
Best regards
Michael
Are you using IPv4 or IPv6?
IPv4
Best regards
Michael
Regards,
Schoch Christian
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