I've been doing some work on Mininet but still confused on some issues below:
1. As we know,a controller, say POX, can set up a connection to a switch based
on TCP,and then communicate with it using Openflow messages. Must the
contrller connect to one or more switches directly? Is it able to control a
switch via another switch?
2.When the switches form a loop, how will the controller handle the connections
and links?I create a topo in mininet:
mininet> netc0s1 lo: s1-eth1:h1-eth0 s1-eth2:s2-eth2 s1-eth3:s3-eth3s2 lo:
s2-eth1:h2-eth0 s2-eth2:s1-eth2 s2-eth3:s3-eth2s3 lo: s3-eth1:h3-eth0
s3-eth2:s2-eth3 s3-eth3:s1-eth3h1 h1-eth0:s1-eth1h2 h2-eth0:s2-eth1h3
h3-eth0:s3-eth1
And then startup the POX controller,using the l2_multi component which will
detect the links and calculate the shortest path between the nodes,here are the
link detect INFOS, all correct:INFO:openflow.discovery:link detected:
00-00-00-00-00-02.3 -> 00-00-00-00-00-03.2DEBUG:openflow.discovery:Dropping
LLDP packet 10915INFO:openflow.discovery:link detected: 00-00-00-00-00-02.2 ->
00-00-00-00-00-01.2INFO:openflow.discovery:link detected: 00-00-00-00-00-03.3
-> 00-00-00-00-00-01.3INFO:openflow.discovery:link detected:
00-00-00-00-00-03.2 -> 00-00-00-00-00-02.3INFO:openflow.discovery:link
detected: 00-00-00-00-00-01.3 ->
00-00-00-00-00-03.3INFO:openflow.discovery:link detected: 00-00-00-00-00-01.2
-> 00-00-00-00-00-02.2
and there exist many errors:
ERROR:openflow.of_01:[Con 2/1] OpenFlow Error:[Con 2/1] Error: header:[Con 2/1]
Error: version: 1[Con 2/1] Error: type: 1 (OFPT_ERROR)[Con 2/1] Error:
length: 28[Con 2/1] Error: xid: 61[Con 2/1] Error: type:
OFPET_BAD_REQUEST (1)[Con 2/1] Error: code: OFPBRC_BUFFER_EMPTY (7)
I can't make it where the error come from.
and then,another problem is the path installed:
DEBUG:forwarding.l2_multi:Installing path for 00:00:00:00:00:02 ->
00:00:00:00:00:01 0800 (2 hops)
if the l2_multi component has calculated the shortest path ,shouldn't it just
have 1 hop?
Any idea or comment would be highly appreciated.Thanks.
Jin mingshuang
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