[j-nsp] Problem with 802.1p/802.1q priority values and MX / EX4200

[Sebastian Wiesinger]

Hello,

we're having a strange problem with 802.1p priority values:

Packets are forwarded by VPLS. A MX960 (MPC/Trio) then forwards them
onto an EX4200 virtual chassis from where they are forwarded to an
external service provider (SP) as a VLAN tagged link.

While testing the line we noticed that packets were dropped by the
SP. Further testing showed that all packets that were dropped had a
VLAN priority value of 2. The SP is dropping packets with these value.

In Wireshark it reads like this:

802.1Q Virtual LAN, PRI: 2, CFI: 0, ID: 468

Now if I apply a firewall filter which tests for these values on the
MX960 outgoing interface (connected to the EX4200) it counts none:

swiesinger at rt1# run show firewall filter vlan-prio-test

Filter: vlan-prio-test
Counters:
Name                                                Bytes              Packets
vlan-prio-test-high-prio                             0                    0
vlan-prio-test-normal-prio                        3420                   30

When I apply the same filter on the incoming interface of the EX4200 I see:

swiesinger at sw1# run show firewall filter vlan-prio-test

Filter: vlan-prio-test
Counters:
Name                                                Bytes              Packets
vlan-prio-test-high-prio                          1830                   15
vlan-prio-test-normal-prio                          1342                   11

Notice that not all packets have a priority value != 0, only some of
them.

So it seems one of the devices is lying to me or the switch is doing
some sort of implicit rewriting on the link.

The connection between the MX960 and the EX4200 is an AE interface
with MC-AE/MC-LAG on the MX side.

I tried forcing all packets to best-effort/loss-priority low on the MX
but that didn't change anything. I'm currently suspecting the EX4200
to be the problem.

Did anyone else experience something like this or has a clue where to
look for the cause of this?

Regards

Sebastian

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