I try to understand the differences between Catalyst 9800 and AireOs and the corresponding consequences for the network. Topic for today is Multicast / IGMP handling for local mode APs (no Flex, no SDA).
So in AireOS, the user VLANs/interfaces (dynamic) had an IP address, because of DHCP relay and IGMP proxy.
IGMP snooping is supported on WLC to better direct multicast packets. When this feature is enabled, the controller gathers IGMP reports from the clients, processes the reports, creates unique multicast group IDs (MGIDs) from the IGMP reports after checking the Layer 3 multicast address and the VLAN number, and sends the IGMP reports to the infrastructure switch. The controller sends these reports with the source address as the interface address on which it received the reports from the clients.
So, the wired layer-3 instance only gets IGMP reports from the WLC dynamic interface source IP adress on behalf of the wireless clients.
The C9800 typically does not have a layer-3 interface (SVI) for the wireless user VLANs, except the "bonjour gateway" shall be used. So the WLC does not act as an IGMP proxy in any way, right?
- All IGMP queries from the wired network to the wireless network are forwarded to ALL APs. The APs have their own IGMP/MGID table and manage those queries
- All IGMP reports from the wireless clients to the wired network are forwarded.
- All IGMP queries from the wired network to the wireless network are forwarded to ALL APs. The APs have their own IGMP/MGID table and manage those queries
- All IGMP reports from the wireless clients to the wired network are forwarded.
Here is what I found on 9800 config guide, which should help you to understand it. Those IGMP queries should be destined to the given multicast group address that they intend to subscribe to.
"Internet Group Management Protocol (IGMP) snooping is introduced to better direct multicast packets. When this feature is enabled, the device snooping gathers IGMP reports from the clients, processes them, creates unique multicast group IDs (MGIDs) based on the Layer 3 multicast address and the VLAN number, and sends the IGMP reports to the IGMP querier. The device then updates the access-point MGID table on the corresponding access point with the client MAC address. When the device receives multicast traffic for a particular multicast group, it forwards it to all the access points, but only those access points that have active clients listening or subscribed to that multicast group send multicast traffic on that particular WLAN. IP packets are forwarded with an MGID that is unique for an ingress VLAN and the destination multicast group. Layer 2 multicast packets are forwarded with an MGID that is unique for the ingress VLAN"
- All IGMP queries from the wired network to the wireless network are forwarded to ALL APs. The APs have their own IGMP/MGID table and manage those queries
- All IGMP reports from the wireless clients to the wired network are forwarded.
Here is what I found on 9800 config guide, which should help you to understand it. Those IGMP queries should be destined to the given multicast group address that they intend to subscribe to.
"Internet Group Management Protocol (IGMP) snooping is introduced to better direct multicast packets. When this feature is enabled, the device snooping gathers IGMP reports from the clients, processes them, creates unique multicast group IDs (MGIDs) based on the Layer 3 multicast address and the VLAN number, and sends the IGMP reports to the IGMP querier. The device then updates the access-point MGID table on the corresponding access point with the client MAC address. When the device receives multicast traffic for a particular multicast group, it forwards it to all the access points, but only those access points that have active clients listening or subscribed to that multicast group send multicast traffic on that particular WLAN. IP packets are forwarded with an MGID that is unique for an ingress VLAN and the destination multicast group. Layer 2 multicast packets are forwarded with an MGID that is unique for the ingress VLAN"
==> All IGMP reports from the wireless clients to the wired network are forwarded.
Right?
My understanding is WLC should snoop it as IGMP snooping enabled on wireless user vlans by default. I haven't test & see it myself though. This document also useful and indicate WLC will snoop IGMP
Yeah, the WLC snoops IGMP. Caution: if interface groups (vlan groups) are used, the Multicast VLAN is mandatory (differs from AireOS), otherwise IGMP queries are not sent to the wireless clients. I consider this a bug.
Anyway... what I'm missing right now is the MGID table on the APs. With AireOS there was the possibility to check the MGID table on the APs. With IOS-XE 17.3 I can only see, that there is an MGID (Index, MGID, Group, VLAN)... However I don't see on which APs the MGID is applied.
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