[j-nsp] Finding drops

[James Bensley]

On Mon, 21 Jan 2019 at 20:09, Jason Lixfeld <jason-jnsp at lixfeld.ca> wrote:
>
> Hi all,
>
> I’m doing some RFC2544 tests through an MX204.  The tester is connected to et-0/0/2, and the test destination is somewhere out there via et-0/0/0.  64 byte packets seem to be getting dropped, and I’m trying to find where on the box those drops are being recorded.
>
> I’ve distilled the test down to generating 100 million 64 byte (UDP) packets to the destination, but the counters on et-0/0/2 read as though they’ve only received about 76.6% of those packets.
>
> If I change the test to send 100 million 100 byte packets, the counters on et-0/0/2 account for all packets.
>
> I’ve tried looking at various output to find a counter that registers the missing packets, but I’m not having any luck.
>
> Aside from 'show interface et-0/0/2 extensive’, I’ve looked here with no luck:
>
> show interface queue et-0/0/2
> show pfe statistics traffic detail
> show pfe statistics exceptions
> show pfe statistics error
>
> Somewhere else I should be looking?

Hi Jason,

To me there are two variables here; speed and packet size. You are
sending 64B packets and experiancing issues but at what rate? 40Gbps
line rate (circa 59.4Mpps)? When you are sending 100B packets you are
not experiancing issues, at what rate is this, 40Gbps (circa 41.6Mpps)
too?

When sending larger packets (100B) the PPS rate would be lower to
achieve line rate @ 40Gbps so two things have changed between the
working and non-working that tests. To try and reduce this to a single
variable (packet size only) does you tester support any sort of packet
pacing, i.e. can you sending 64B packets but at less than line rate?
For example, can you transmit at a rate of 10Gbps of 64B packets
(circa 14.4Mpps) instead of 40Gpbs of 64B packets (circa 59.5Mpps) and
see if all the packets are counted on your ingress interface?

On a side note, when you say that the packet counters on the MX
receiving interface are missing packets, what about the transmitting
interface and the receiving RFC2544 tester? Do they also show the
packets as missing (so they were dropped) or do they show the correct
number of packets received and it's just the MX receiving interface
that isn't accounting for all packets BUT all packets are forwarded?

Cheers,
James.