[nznog] UFB 2M upload issues - DEI markings - Juniper

5 Nov 2014

      Hi all

We have finally fixed our 2M upload issues on Chorus UFB accelerate plans.
Skip to the end of this email if you just want an example fix.

Along the way we established a couple of incorrect "facts". Some of which I
shared with this list.

These were:
1) DEI marked packets were being silently dropped on ingress from the
Chorus handover
2) Junos 12.3 fixed this issue

Recently I deemed that "fact" 1) was wrong and hence "fact" 2) was a bit
irrelevant.

Here's a crude diagram of our typical set-up:

<Chorus handover> <-> [1] <MX80> [2] <-> MPLS/VPLS over Backhaul fibre <->
[3] <PMR MPLS MX> [4] <-> [5] <PMR BNG>

Where the numbers in the square brackets are interfaces where I performed
some traffic stats.

I deemed that DEI=1 marked packets were still showing up at [1] and [3].
They were not showing up at interfaces [4] and [5]. This deemed my above
"facts" incorrect.

With Juniper CoS you classify on ingress and rewrite on egress. Once we
deemed that DEI marked packets were not being dropped at [1] and instead
were being dropped between [3] and [4] we can now rewrite these before
interface [4]. As we need to rewrite on egress we'll do this at point [2].

In our test case interface [2] is actually xe-1/2/0.388 . And a simple fix
for the issue is under the class-of-service section implement:

interfaces {
    xe-1/2/0 {
        unit 388 {
            rewrite-rules {
                ieee-802.1ad {
                    ieee-802.1ad-dei-rewrite;
                    vlan-tag outer;
                }
            }
        }
    }
}
rewrite-rules {
    ieee-802.1ad ieee-802.1ad-dei-rewrite {
        forwarding-class best-effort {
            loss-priority low code-point 0000;
            loss-priority high code-point 0000;
        }
    }
}

The key is to use a ieee-802.1ad rewrite rule rather than a ieee-802.1
rule. The leftmost bit of the 4 bit code-point is the DEI bit. This is all
assuming that all traffic is classified as best-effort at interface [1] -
if that is not the case then re-write the DEI bit for your other queues as
well.

You only need to rewrite the outer vlan DEI bit.

This is tested on Junos 12.3R8.7 on a MX80.

Thanks to all involved in helping fix this - Steve K, Vance and Ivan
especially.

Cheers
Dave

[nznog] UFB 2M upload issues - DEI markings - Juniper

Dave Mill