Following on from my look at Juniper WXC and WCCP for resilient sites, it transpires that the issue with IGMP snooping needing to be disabled on certain switches is due to the partial implementation of the multicast IP support within the Juniper WXOS software.
For switches that have IGMP snooping feature, this normally enabled on these switches, and most support IGMP v2. This requires both the multicast end device to advise that the multicast group has been joined, but also that the multicast router to query the end device periodically to determine if the device is still actively part of that group.
IGMP snooping on the switch monitors these messages and enables or disables the forwarding of multicast packets to the particular port that responds, and closes off the port if no membership report information is returned to the router. Because the Juniper does not support IGMP v2, these switches will withdraw the multicast forwarding for the Juniper WXC port as it’s not part of the multicast group that the switch recognises via IGMPv2.
Disabling the IGMP snooping prevents the shutdown of the multicast traffic to non-member ports, and instead floods the multicast traffic to all ports, similar to broadcast traffic processing. As this traffic is now forwarded to the Juniper (and incidentally to all other devices connected to the switch), the WCCP relationship between the Juniper and the routers is maintained. Correct operation of this feature can be seen using the show packet-interception command. This will show the HereIAm and ISeeYou WCCP messages (HereIAm is issued by the Juniper, ISeeYou comes from the routers). Both should be increasing, if the IGMP issue occurs, what is shown is the HereIAm messages continue to be emitted, but the returned ISeeYou messages are prevented from reaching the Juniper via the switch, and this counter stops.
Time for a feature request, methinks..
This post was valid at the time written, but has not been updated to support the latest release of WXOS or JWOS. See www.juniper.net for more information on later releases and if this is fixed.
