Hello all,
I am currently building a monitoring component on top of NOX.
As part of monitoring I am trying to make use of the transaction id
field (xid) in open flow messages to detect whether stats replies from
switches are being lost, delayed or re-ordered.
The simplified scenario we have in mind is shown below where stats
replies from a switch are delayed or reordered:
collection
window
(time t): | t=1 | t=2
switch 1: | stats_req1(sw1) | stats_req2(sw1)
| stats_reply1(sw1) | stats_reply2(sw1)
-----------------------------------------------------------
switch 2: | stats_req1(sw2) | stats_req2(sw2)
| [reply delayed] | stats_reply1(sw2), stats_reply2(sw2) OR
| | stats_reply2(sw2), stats_reply1
I have 4 questions about event delivery in NOX:
1) When stats request messages are issued from a python component is a
transaction id (xid) set in the openflow message header automatically by
the underlying controller/C++ plumbing? Are there any examples in python
of setting the xid on an outgoing stats request message (or other type
of openflow message)? The ripcord flowinstaller is close just wondering
if a better example existed?
2) When NOX delivers an event to a component, is there a way to
access/check the xid associated with the event message or is this
information stripped off by the controller before passing the event onto
the component?
Looking at the guts of a port stats reply event it looks like the low
level details like xid either a) were not set automatically b) have been
stripped off before handing the event to the component or c) may be
hidden behind the opaque pyevent*:
{'this': <Swig Object of type 'pyevent *' at 0xadc58d8>, 'datapath_id':
150874213227L, 'ports': [{'rx_over_err': 0L, 'tx_dropped': 0L,
'rx_packets': 0L, 'rx_frame_err': 0L, 'rx_bytes': 0L, 'tx_errors': 0L,
'rx_crc_err': 0L, 'collisions': 0L, 'rx_errors': 0L, 'tx_bytes': 1380L,
'rx_dropped': 0L, 'tx_packets': 69L, 'port_no': 0}, {'rx_over_err': 0L,
'tx_dropped': 0L, 'rx_packets': 0L, 'rx_frame_err': 0L, 'rx_bytes': 0L,
'tx_errors': 0L, 'rx_crc_err': 0L, 'collisions': 0L, 'rx_errors': 0L,
'tx_bytes': 1360L, 'rx_dropped': 0L, 'tx_packets': 68L, 'port_no': 1}]}
3) If a stats request message goes unanswered does a subsequent stats
request message to the same switch supersede it. In the toy example does
stats_req2(sw2) cause any late replies to stats_req1(sw2) to be
ignored/dropped?
4) Do stats request messages time out? If so is there a way to be
notified of the time out?
by the way, which mailing list is appropriate for these kinds of questions?
thanks,
Rean
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