[ovs-discuss] Query on DEC_ttl action implementation in datapath

bindiya Kurle bindiyakurle at gmail.com
Thu Aug 29 03:22:35 UTC 2019


Thanks. Is there any forum where i can discuss the design for same?

Regards,
Bindiya

On Thu, Aug 29, 2019 at 1:22 AM Justin Pettit <jpettit at ovn.org> wrote:

> I understand.  This has been discussed previously on the mailing list.
> You are welcome to submit a patch upstream to provide that capability, but
> I suspect you will get some resistance--especially from the Linux kernel
> community.
>
> --Justin
>
>
> > On Aug 27, 2019, at 11:25 PM, bindiya Kurle <bindiyakurle at gmail.com>
> wrote:
> >
> > Hi Justin,
> >
> > Thanks for the clarification. I agree to your point ,but consider a
> use-case if I have routing decision only based on destination ip then as
> per current implementation, ovs will add 2 flows (in data path)for packets
> coming from different source and if the TTL happens to be different for
> them .This will reduce number of flows that can be supported with ovs. If
> decrement TTL  was done in kernel ,it would have ended in adding one flow
> only.
> >
> > Regards,
> > Bindiya
> >
> > Regards,
> > Bindiya
> >
> > On Tue, Aug 27, 2019 at 9:48 PM Justin Pettit <jpettit at ovn.org> wrote:
> > I think it was considered cleaner from an ABI perspective, since it
> doesn't require another action, since "set" was already supported.  In
> practice, I don't think it's a problem, since usually a TTL decrement is
> associated with a routing decision, and TTLs tend to be fairly static
> between two hosts.
> >
> > --Justin
> >
> >
> > > On Aug 27, 2019, at 1:11 AM, bindiya Kurle <bindiyakurle at gmail.com>
> wrote:
> > >
> > > hi ,
> > > I have a question related to dec_ttl action implemented in datapath.
> > > when  dec_ttl action is configured in OVS following action get added
> in datapath.
> > >
> > > recirc_id(0),in_port(2),eth(),eth_type(0x0800),ipv4(ttl=64,frag=no),
> packets:3, bytes:294, used:0.068s, actions:set(ipv4(ttl=63)),3,
> > >
> > > if packet comes with different TTL on same port then one more action
> get added in datapath.
> > > for ex:
> > > recirc_id(0),in_port(2),eth(),eth_type(0x0800),ipv4(ttl=9,frag=no),
> packets:3, bytes:294, used:0.068s, actions:set(ipv4(ttl=8)),3,
> > >
> > > Could someone please explain why dec_ttl is implemeted as a set
> action  rather than dec_ttl action.
> > >
> > >
> > > I mean , why for different ttl one more rule get added rather than
> just adding it as  following as done in userspace
> > >
> > > recirc_id(0),in_port(3),eth(),eth_type(0x0800),ipv4(frag=no),
> packets:3, bytes:294, used:0.737s, actions:dec_ttl,2
> > >
> > > Regards,
> > > Bindiya
> > > _______________________________________________
> > > discuss mailing list
> > > discuss at openvswitch.org
> > > https://mail.openvswitch.org/mailman/listinfo/ovs-discuss
> >
>
>
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