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ENWLSI 300-430 study materials
ENWLSI 300-430 study resources

ENWLSI 300-430: Implementing and Configuring Cisco Wireless Multicast and mDNS

ENWLSI 300-430 · Work through your exam, one topic at a time.

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Implementing and Configuring Cisco Wireless Multicast and mDNS

The Implementing and Configuring Cisco Wireless Multicast and mDNS domain tests how the controller delivers group traffic to wireless clients and how Bonjour discovery crosses VLAN boundaries.

Multicast forwarding modes

  • Unicast mode: the controller replicates each packet per client. No wired multicast is needed, but it scales badly.
  • Multicast (multicast-multicast): one copy per WLAN is sent to a multicast group, and the APs replicate over the air. Clients are mapped to a multicast group ID (MGID) per VLAN.
  • Multicast-direct: the APs join the group and forward traffic directly onto the wired network; requires multicast routing (PIM) in the infrastructure.
  • AP multicast mode moves replication to the AP level and likewise depends on multicast-enabled wired networks.

IGMP snooping and group membership

  • The controller snoops client IGMP reports to learn which clients belong to which group. Enable global multicast mode and IGMP snooping, or clients join the WLAN but never receive group traffic.

mDNS / Bonjour gateway

  • The mDNS gateway snoops mDNS queries on the WLAN and answers on behalf of devices in other VLANs, converting multicast to unicast.
  • You enable the gateway, then attach a service policy/profile listing the services you allow, such as _airplay._tcp.local, _raop._tcp.local, _ipp._tcp.local or _googlecast._tcp.local.
  • Catalyst 9800 attaches the mDNS service policy in the policy profile; AireOS ties an mDNS profile to the WLAN/interface. With FlexConnect local switching, the AP must run in mDNS AP mode so it snoops and caches locally.

Worked example

An Apple TV on VLAN 20 is visible to clients on VLAN 20 but invisible to clients on VLAN 30. Reasoning: same-subnet discovery is link-local multicast and needs nothing from the controller; cross-VLAN discovery needs the gateway. Enable the mDNS gateway, create a service policy containing _airplay._tcp.local, attach it to the VLAN 30 policy profile, and confirm query counters increase. If discovery still fails, the service string is usually missing or misspelled.

Traps that cost marks

  • Multicast enabled but IGMP snooping left off, so clients receive no group traffic.
  • Multicast-direct or AP multicast mode deployed without PIM/multicast routing on the wired network.
  • An mDNS policy that omits the specific service the client is browsing for.
  • Expecting controller mDNS to work for FlexConnect locally switched clients without mDNS AP mode.