[ovs-discuss] Port range matching

Nicholas Bastin nick.bastin at gmail.com
Sun Aug 7 16:54:53 PDT 2011

On Fri, Aug 5, 2011 at 03:06, Yaxuan <yaxuan at tsinghua.edu.cn> wrote:

> Although it is not difficult to implement Range-match on OvS, it is
> definitly a bad thing for hardware-based OpenFlow switches.**
> **
> **

Range-match should be an interface-provided convenience that your controller
or northbound API should provide for you.  Internally it would still gets
converted to N individual entries.  You could of course extend the protocol
if you wanted to add range-match support in a single flow entry, but as you
say, generally hardware doesn't support this match (although in theory
things like NetFPGA and network-processor-driven data planes could).

In the worst case, 1 range can expand to 2(W-1) prefixes, where W is the
> bit-width of a header field (e.g. W=16 for L4 port fields). So for the TCAM
> based hardware, it might waste many TCAM entries for a single rule.

It shouldn't waste any more than what you would actually do if you didn't
have range functionality, however, and presumably the user knows what
they're doing (har har, I guess).

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