Thanks Murphy, Finally got it to work. I set the ToS bits in my packet generation code as 4. And set a match for nw_tos=4 on the switch. This was a little confusing.
On Sun, Dec 8, 2013 at 11:54 PM, Murphy McCauley <murphy.mccau...@gmail.com>wrote: > The issue you're having is described on page 24 of the OpenFlow spec as > well as on the ovs-ofctl man page, but without some context, it may not > entirely make sense. Specifically, the spec says: > The nw_tos fi eld is the 6 upper bits of the ToS field to set, in the > original bit positions (shifted to the left by 2). > > To understand this better: nw_tos is actually not really to do with the > TOS field (which is long retired), but with the DiffServ field which > superseded it. The bottom two bits of this field were originally unused, > and later became the ECN bits. The top six bits are the DiffServ Code > Point (DSCP), which is what nw_tos actually matches (right; it should > actually probably be called nw_dscp). > > So the value you give to OpenFlow for nw_tos is actually a six bit field > -- the top six bits of eight. One might imagine that the values of this > field would therefore be 0 through 63, and would be shifted up two bits > when written to the packet. However, as the spec says, these are "in the > original bit positions". Thus, the smallest value legal for this field is > 4 (followed by 8 and then 12, etc.). > > TLDR: You can't set the bottom two bits. You want one of the following, > though it's hard to say which for sure: 1) to shift what you think the > value should be to the left by two, or 2) to set the ECN bits and not the > "TOS" (DSCP) bits. > > -- Murphy > > On Dec 8, 2013, at 11:12 PM, Sameer Katti <ska...@usc.edu> wrote: > > > Hi All, > > > > I am trying to set a flow that matches based on the nw_tos field of the > match object. But when I dump the flows on the switch it has nw_tos field > set as 0. > > I am using OpenvSwitch 1.10 on Mininet 2.0 > > The code snippet I am using is:- > > > > msg = of.ofp_flow_mod() > > #msg.match.dl_dst = packet.dst > > msg.match.dl_type = ethernet.IP_TYPE > > msg.match.nw_tos = 1; > > > > Even after installing a flow with such a match the nw_tos is still set > to zero. > > > > *** s1 > ------------------------------------------------------------------------ > > NXST_FLOW reply (xid=0x4): > > cookie=0x0, duration=13.677s, table=0, n_packets=1, n_bytes=98, > idle_age=12, ip,dl_dst=d2:35:53:03:83:bc,nw_tos=0 actions=output:1 > > cookie=0x0, duration=6.652s, table=0, n_packets=3, n_bytes=294, > idle_age=3, ip,dl_dst=da:79:78:e1:7c:4f,nw_tos=0 actions=output:2 > > > > > > How should I set the nw_tos field in ofp_match object? > > -- > > -Sameer > > -- -Sameer
