Re: xdp-cpumap-tc multi queue schema and traffic mirroring

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"Ethy H. Brito" <ethy.brito@xxxxxxxxxxxx> writes:

> On Thu, 07 Oct 2021 19:02:58 +0200
> Toke Høiland-Jørgensen <toke@xxxxxxxxxx> wrote:
>
>> "Ethy H. Brito" <ethy.brito@xxxxxxxxxxxx> writes:
>> 
>> > Hi All
>> >
>> > Before I moved to XDP cpumap bandwidth control "philosophy" I used to snoop
>> > inside the htb classes (mainly the default one) mirroring traffic to a
>> > dummy interface then run tcpdump on that like:
>> >
>> > 	tc filter add dev eth0 parent 1: protocol all prio 0xffff \
>> > 	u32 match u32 0 0 flowid 1:$shp action mirred egress mirror dev
>> > dummy0
>> >
>> > Then "tcpdump -npi dummy0" used to show me all that classid "1:$shp" was
>> > carrying.
>> >
>> > Now, with the multi queue environment XDP creates, I can't make mirroring
>> > to work. For instance: I need to see what is going on with HTB classid
>> > e:102, so I tried: 
>> > 	tc filter add dev eth0 parent e: ... e:102 action mirred egress ...
>> >
>> > and "tcpdump -npi dummy0" prints traffic that has nothing to do with
>> > classid e:102. I can confirm the traffic is pored thru the class since its
>> > bandwidth is controlled/limited correctly.  
>
>
> Hi Toke, et All.
>
>> 
>> The xdp-cpumap-tc utility will attach a filter to the egress interface,
>> presumably that is taking priority and short-circuit your mirred filter?
>
> This makes sense. 
> But How to circumvent this??
>
> Snooping the default class (classes, in xdp-cpumap case) is essencial
> to catch misconfigured mappings.

Well, it's possible to chain multiple filters, they just need to be
configured properly. Not sure exactly what the right incantation is, but
it'll likely require at least changing the priority of the filter
installed by xdp-cpumap. I'd suggest you open an issue on the github
repository, as that is really the appropriate place to discuss this, as
it's not really XDP-specific...

-Toke





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