2

I've got a single MX router connected to two physical interfaces on an SRX chassis cluster - each interface being a member of a reth interface.

In order to make this work, on the MX side I have the interface from each SRX node connected into a bridge-domain, which in turn has an irb configured on it for the L3 interface. This all works fine.

I now want to schedule egress traffic from the MX (received and classified on another interface) into an appropriate forwarding class, however the MX (currently) does not support applying a scheduler to an irb interface.

Has anyone come across a way of doing this on the MX?

  • I’m not well versed in Junos, but scheduling happens on physical interfaces, not logical ones. So the CoS markings would be used. – Ron Trunk Apr 22 '18 at 12:37
  • That's my take too, but because the physical interfaces assigned to a bridge-domain are L2, the DSCP classifier I'm using is not having any effect. I've also tried an IEEE-802.1 re-write, but this doesn't work because you need to assign traffic to a forwarding-class before you can differentiate it for re-write. – Benjamin Dale Apr 22 '18 at 14:17
1

So I just came up with a hideous hack that gives the desired result:

firewall {
    family inet {
        filter DSCP-CLASSIFIER {
            term MATCH-EF {
                from {
                    dscp ef;
                }
                then {
                    forwarding-class VOICE-FC;
                    accept;
                }
            }
            term MATCH-ALL {
                then {
                    forwarding-class BE-FC;
                    accept;
                }
            }
        }
    }
}
interfaces {
    irb {
        unit 100 {
            family inet {
                filter {
                    output DSCP-CLASSIFIER;
                }
                address 192.168.88.3/31;
            }
        }
    }
}

bdale@lab-mx80a> show interfaces queue ge-1/0/4.100
  Logical interface ge-1/0/4.100 (Index 334) (SNMP ifIndex 850)
Forwarding classes: 16 supported, 5 in use
Egress queues: 8 supported, 5 in use
Burst size: 0
Queue: 0, Forwarding classes: BE-FC
  Queued:
    Packets              :                176357                     0 pps
    Bytes                :              21939946                     0 bps
  Transmitted:
    Packets              :                176357                     0 pps
    Bytes                :              21939946                     0 bps
    Tail-dropped packets :                     0                     0 pps
...
Queue: 1, Forwarding classes: VOICE-FC
  Queued:
    Packets              :                    69                     1 pps
    Bytes                :                  8694                   896 bps
  Transmitted:
    Packets              :                    69                     1 pps
    Bytes                :                  8694                   896 bps
    Tail-dropped packets :                     0                     0 pps
...

This works because the traffic that I’m sending is already pre-marked with DSCP; even though it is being classified by an EXP classifier on an ingress MPLS interface and that’s what we should really be using to determine forwarding-class on the egress interface, but obviously because it’s a non-mpls interface, we don’t see the EXP on egress.

It bugs me that the box is clearly capable of scheduling egress traffic from an irb in this manner, but doesn’t support it in the more traditional (and saner) way through the CoS stanza.

If you’ve got any better ideas, I’m all ears!

  • I suspected you were going to have such a problem. The incompatible layer-2 QoS and having layer-3 QoS just is a mess. It is difficult, and you can have conflicting layer-2 and layer-3 QoS, but mixing MPLS EXP layer-2 and ethernet CoS layer-2 just seems like a difficult proposition. – Ron Maupin Apr 23 '18 at 3:05
  • it's just the irb/bridge-domain that causes issues. If I switch to a single L3 link, or L3 AE, everything works swimmingly (classify based on DSCP/EXP/802.1P depending on interface type to forwarding class, re-write markings based forwarding class and egress interface type) – Benjamin Dale Apr 23 '18 at 4:07

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