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Multicast, mDNS/Bonjour configuration across subnets

SonicAdmin80SonicAdmin80 Cybersecurity Overlord ✭✭✭
in Mid Range Firewalls

I'm reading up on multicast & mDNS across VLANs with SonicWall and I came across these two articles:

https://www.sonicwall.com/support/knowledge-base/configuring-multicast-dns-for-apple-bonjour-on-gen-5-and-gen-6-sonicwall-appliances/170503725498663

https://www.sonicwall.com/support/knowledge-base/configuring-multicast-dns-for-apple-bonjour-on-sonicwall-with-ios-airprint-support/170505405308995

They seem to have contradicting and out of date information. For example the one with a Multicast configuration example says "IP Helper is not needed. In fact, it doesn't have mDNS support. mDNS support was added on GEN 5." while the other says to configure IP Helper.

Has anyone done this recently? Do I need to configure Multicast or IP Helper or both? And is a NAT rule required in addition to an access rule?

Category: Mid Range Firewalls
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Answers

  • BWCBWC Cybersecurity Overlord ✭✭✭

    I don't do much with Multicast, but my configuration at home comes down to this.

    FW.jpg

    This address group currently holds a single object for 224.0.0.251 (mDNS) in the Multicast Zone.

    Multicast support is enabled in the Advanced section of the interface which houses my AppleTV and on the Interfaces where my different WLAN SSIDs are attached.

    Access Rules into the MULTICAST zone are only the defaults. But you need Access Rules to allow client traffic (e.g. WLAN clients) to the destination (e.g. Apple TV).

    That's it, no IP Helper no nothing. You have to make sure that Access Points or Switches do not mess with your Multicast traffic.

    —Michael@BWC

  • SonicAdmin80SonicAdmin80 Cybersecurity Overlord ✭✭✭

    Thanks @BWC, so no special NAT rules at all between zones?

    I’ll try to do this with Sonos in a business network, so both mDNS and SSDP might be required but hopefully it’s this simple.

  • BWCBWC Cybersecurity Overlord ✭✭✭
    edited February 26

    No NAT rules, I can't see a reason why, because all traffic is routed through the SNWL (when configured as gateway).

    But you might check the Access Rules from LAN (or WLAN) to MULTICAST, I'am not sure if they are set to "Allow" by default.

    —Michael@BWC

  • SonicAdmin80SonicAdmin80 Cybersecurity Overlord ✭✭✭
    https://community.sonicwall.com/technology-and-support/discussion/comment/23226#Comment_23226

    NAT was mentioned in one of those articles and I get that it might be a requirement in certain scenarios if the device connected to doesn't like answering to traffic not originating from the same subnet, but perhaps it depends on the service and implementation.

    I'll give multicast configuration a go and I'll find out soon enough if it works.

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