• IGMP snooping not working as expected.
• Customer has multicast traffic running over bridge-domain.
• MX devices are running in MC-LAG A/A. Traffic received from downstream SW's sent across inter-chassis link(AE1) even though there is no receiver.
• This is causing high utilization on one of the member links of AE1. Need you assistance to understand this behavior.

user@router> show igmp snooping interface ae1.1102 detail
Instance: default-switch
Bridge-Domain: __%name%changed%__
Learning-Domain: default
Interface: __%name%changed%__
State: Up Groups: 0 >>>>>>>
Immediate leave: Off
Router interface: no


Configured Parameters:
IGMP Query Interval: 125.0
IGMP Query Response Interval: 10.0
IGMP Last Member Query Interval: 1.0
IGMP Robustness Count: 2






user@router> show multicast snooping route bridge-domain __%name%changed%__ group 239.8.A.A extensive
Nexthop Bulking: OFF


Family: INET


Group: 239.8.A.A/32
Source: X.X.X.X/32
Bridge-domain: __%name%changed%__
Mesh-group: __%name%changed%__
Downstream interface list:
ae1.1102 -(730) <<<<<<<<<
Statistics: 89545 kBps, 65171 pps, 30942392108 packets
Next-hop ID: 1048666
Route state: Active
Forwarding state: Forwarding








user@router> show igmp snooping membership bridge-domain __%name%changed%__
Instance: default-switch


Bridge-Domain: __%name%changed%__


Learning-Domain: default
Interface: ae1.1102, Groups: 0


Learning-Domain: default
Interface: ae4.1102, Groups: 21
Group: 224.0.x.x
Group mode: Exclude
Source: 0.0.0.0
Last reported by: x.x.x.x
Group timeout: 210 Type: Dynamic
Group: 224.0.y.y
Group mode: Exclude
Source: 0.0.0.0
Last reported by: x.x.x.x
Group timeout: 203 Type: Dynamic
Group: 224.0.z.z
Group mode: Exclude
Source: 0.0.0.0
Last reported by: x.x.x.x
Group timeout: 202 Type: Dynamic
Group: 224.0.a.a
Group mode: Exclude
Source: 0.0.0.0
Last reported by: x.x.x.x
Group timeout: 209 Type: Dynamic
Group: 224.0.b.b
Group mode: Exclude
Source: 0.0.0.0
Last reported by: y.y.y.y
Group timeout: 210 Type: Dynamic
Group: 224.0.c.c
Group mode: Exclude
Source: 0.0.0.0
Last reported by: d.d.d.d
Group timeout: 210 Type: Dynamic
Group: 224.0.e.e
Group mode: Exclude
Source: 0.0.0.0
Last reported by: x.x.x.x
Group timeout: 200 Type: Dynamic
Group: 224.0.f.f
Group mode: Exclude
Source: 0.0.0.0
Last reported by: x.x.x.x
Group timeout: 200 Type: Dynamic
Group: 239.8.g.g
Group mode: Exclude
Source: 0.0.0.0
Last reported by: y.y.y.y
Group timeout: 204 Type: Dynamic









user@router> show configuration bridge-domains %name_changed& | display inheritance no-comments
description %name_changed&;
domain-type bridge;
vlan-id %name_changed&;
interface ae1.1102;
interface ae4.1102;
interface ae7.1102;
interface ae8.1102;
interface ae9.1102;
interface ae479.1102;
routing-interface irb.1102;
forwarding-options {
flood {
input %name_changed&;
}
}
protocols {
igmp-snooping;
}

• For FHR traffic (i.e., when IRB is configured in the bridge-domain): When we have a local interest for the same (S, G) in the same VLAN (i.e., L2 Single homed host or another MCAE (MH host)), the route must forward to ICL only for traffic initiated in the local L2 domain.
• Learn the (S,G) routes from RPD that have IRB as IIF (today we learn only S,G route with IRB as OIF). Install this (S,G) into the table by adding the relevant L2 interfaces with membership and ICL. This will ensure that (*,G) will only have the L2 interfaces and traffic from other sources will not be flooded to ICL.
• For the <S,G> traffic will always carry ICL as per design to ensure that for FHR i.e. source as IRB the routed traffic can be sent to any other L3 Multicast receiver on peer MCLAG router.

Conclusion

• The behavior is expected and we saw with IRB as IIF on FHR the ICL carried traffic.
• When we disabled PIM on IRB we never saw any traffic over ICL

Logs and outputs indicating the same on customer setup

Multicast snooping route 


Group: 239.8.x.x/32
  Source: *
  Bridge-domain: %name_changed%
  Mesh-group: __all_ces__
  Downstream interface list:
    icl -(1048577) aeX.%name_changed% -(768) <<<<<<<<<<<<<<<<<< Includes ICL NH
  Statistics: 0 kBps, 0 pps, 254 packets
  Next-hop ID: 1048669
  Route state: Active
  Forwarding state: Forwarding


Group: 239.8.y,y/32
  Source: y.y.y.y/32
  Bridge-domain: %name_changed%
  Mesh-group: __%name_changed%__
  Downstream interface list:
    ae1.%name_changed% -(730) %name_changed% -(768)   <<<<<<<<<<<<<<<<<<< Includes the ICL(%name_changed%) directly under NH
  Statistics: 34901 kBps, 25401 pps, 36666301795 packets
  Next-hop ID: 1048670
  Route state: Active
  Forwarding state: Forwarding