libtool was needed when NOX was directly linking against libopenflow.
Since it doesn't do that anymore, we can drop its use (and that makes
OpenFlow configure and build slightly faster).
This keeps vlogconf, in particular, from being linked against OpenSSL,
which in turn keeps the Debian package build tools from complaining that
the openflow-common package shouldn't need to depend on OpenSSL but does
because of the spurious library link.
One use case is when NOX is running on localhost, in which case waiting
for the full default backoff interval is unnecessary and undesirable.
Also changes default maximum backoff to 15 seconds (from 60).
It can happen that the secure channel thinks that it is connected
to the controller, but in fact the connection has dropped. For
example, a switch intermediate between the secure channel and the
controller could have a flow inserted, due to a malfunction, that
causes packets in one direction or the other to be dropped. When
this happens, the Linux kernel's TCP implementation will continue
retransmitting packets for somewhere between 13 and 30 minutes,
depending on the connection's retransmission timeout (according
to linux/Documentation/networking/ip-sysctl.txt) with the default
Linux settings.
We want to detect the lost connection and re-connect much faster
than that. We use OpenFlow echo request and reply messages: if
no message is received from the controller for N seconds, we
send out an echo request. If no reply (actually, any message at
all) is received for an additional N seconds, then we assume
that the connection has been lost, and reconnect.
This brings the user-space switch in-line with fixes that were previously
made to the kernel one. The main problem was that when wildcards are used
some of the fields that follow should also be wildcarded.
This allows us to open network devices without bringing them up
and setting them for promiscuous mode, which will be useful in the
secchan for in-band communication.
When the controller wishes to add a flow entry to the switch, it sends a request with a description of matching flows in a "match". The switch was adding these exactly as described into the flow tables. However, when packets arrived, all invalid fields (e.g., the TCP/UDP ports in a non-TCP/UDP packet) are set to zero. If the rule being added by the controller had not set these invalid fields to zero, the packets would never match. We now zero out these fields when extracing a "match".
-- Reported by Brandon H. --
Otherwise, we give the table implementations the opportunity to screw up
by distinguishing between two flows without wildcards but with apparently
different priorities that are required to be treated as the same priority.
Now the number of actions is limited, as a practical matter, to the size
of the buffer that the kernel provides for Netlink dumps, which is usually
4096 bytes. A flow statistics entry must fit in a single one of these
buffers. Actions are 8 bytes each, so this is about 500 actions
considering overhead.
Ben Pfaff
Justin Pettit
root