WLC - mDNS Bridging Between Wired LANs

[tresdodi]

Does a WLC support bridging mDNS between wired LANs only? More accurately, will it respond with mDNS service provider info learnt from wired LANs to mDNS queries coming from wired devices in other LANs? I had assumed so, but debugging today I'm seeing that my AIR-CT2504 refuses to respond to these queries. Wireless to wired works fine; however, logs for tests between wired-only show that the WLC has the record for the requested services but does not send them to the requesting client because "SP on DS side & Query is from DS side." Snippets:

Packet from wired client asking for Chromecast services:

*Bonjour_Msg_Task: May 11 15:25:59.660: 98:09:cf:<elided> Received bonjour packet from DS, vlan id 1, protocol 0x800, SRC MAC 98:09:CF:<elided> , DST MAC 01:00:5E:00:00:FB
*Bonjour_Msg_Task: May 11 15:25:59.660: 98:09:cf:<elided> Processing BONJOUR Packet from Wired

 WLC matches registered Chromecast providers on another wired LAN and starts building the response:

*Bonjour_Msg_Task: May 11 15:25:59.661: Service Name : Chromecast Service String : _googlecast._tcp.local. is supported in MSAL-DB
[...]
*Bonjour_Msg_Task: May 11 15:25:59.661: bgSendQueryResponseMsg : 4178 Sending BONJOUR_AGGREGATED_QUERY_RESPONSE SRV :Chromecast , MsgId :1, dst-Mac :98:09:cf:<elided> , dst-IP :192.168.1.28
[...]
*Bonjour_Process_Task: May 11 15:25:59.663: sendBonjourPkt : 4114 sendBonjourPkt msg-type = BONJOUR_AGGREGATED_QUERY_RESPONSE toSend = Wired

 But then changes its mind before actually attaching the provider info:

*Bonjour_Process_Task: May 11 15:25:59.663: Skipping SP: BRAVIA-4K-VH21-<elided>._googlecast._tcp.local.. SP on DS side & Query is from DS side.
*Bonjour_Process_Task: May 11 15:25:59.663: Skipping SP: Pioneer-VSX-LX105-<elided>._googlecast._tcp.local.. SP on DS side & Query is from DS side.
*Bonjour_Process_Task: May 11 15:25:59.663: buildBonjourQueryResponsePld : 6802 Not able to attach any record
*Bonjour_Process_Task: May 11 15:25:59.663: Error building the Bonjour Packet !!
[...]
*Bonjour_Process_Task: May 11 15:25:59.663: sendBonjourPacketToWired : 3845 Building Bonjour Packet Failed

*Bonjour_Process_Task: May 11 15:25:59.663: Sending bonjour Query to wired host failed.
[...]
*Bonjour_Process_Task: May 11 15:25:59.663: bgSendMdnsQueryToMdnsAp :3699 allMdnsAp = FALSE toSend = BONJOUR_PKT_TO_WIRED
[...]
*Bonjour_Process_Task: May 11 15:25:59.664: sendBonjourPkt : 4345 Sending mDNS query to a mDNS AP failed

Although I'm not sure what "SP" and "DS" mean here; (maybe, Service Provider and Distribution System), my interpretation is that the WLC notices that both client and provider are on wired networks and by design halts the reply. Pointing to that too is the last message "Sending mDNS query to a mDNS AP failed", which seems to indicate that it expected that the query had come from a wireless client.

[marce1000]

 - Ref : https://www.cisco.com/c/en/us/support/docs/wireless/catalyst-9800-series-wireless-controllers/215352-configure-and-troubleshoot-mdns-on-catal.html#toc-hId-721178525
  >...In C9800 Architecture, mDNS (Bonjour Protocol) Bridging refers to the same L2 broadcast domain Bonjour TTL=1 protocol packet forwarding. The dataplane enables mDNS bridging functionality for packets received on the wired ports and wireless interfaces for each WLAN by default. This is the default behavior without specific configuration required, as not even Global mDNS needs to be enabled to allow mDNS Bridging to work,

                     As  a result you may need to migrate to the modern 9800 based controller platforms , 

 M.

[Rich R · Accepted solution]

I agree with your conclusion that it will only service queries from Wireless clients @tresdodi .  The WLC is not supposed to be acting as a LAN switch/router.  It expects that task to be performed by the wired switch or router.

As Marce says 9800 series WLC (with latest software versions) have significant mDNS/Bonjour enhancements.

[tresdodi]

Thanks, @marce1000 and @Rich R. As a quick temporary solution I'll configure an Avahi mDNS reflector in a multihomed Ubuntu machine that is existing.