[ovs-dev] datapath flow will match packet's tll when we use dec_ttl in action

Ben Pfaff blp at ovn.org
Fri Jun 7 17:35:49 UTC 2019


On Wed, May 29, 2019 at 08:26:12PM +0800, ychen wrote:
> hi,
>    when I send IP packets with ttl in IP header is random in range(1-255), and with all other IP header fields stay not changed
>     but generated 255 datapath flows each with different ttl value.
>     of course, i use the action dec_ttl,  here is code:
>     case OFPACT_DEC_TTL:
>             wc->masks.nw_ttl = 0xff; 
> 
> 
>    my question is: can we optimize the dec_ttl action? only differentiate TTL>1 and TTL <=1?
>    as we all know, when TTL=0, we should send packet to the controller, and let it make decision whether we should send icmp error packet out.
>    when TTL is larger than 1, I think they are no difference, am i right?

This optimization is not too valuable, because in practice IP packets
don't have random TTLs.


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