[Bridge] Linux bridge on linksys WRT54GS running OpenWRT

Stephen Hemminger shemminger at osdl.org
Thu Jul 7 10:59:57 PDT 2005

On Thu, 07 Jul 2005 18:37:07 +0200
Olaf Menzel <olaf.menzel at fokus.fraunhofer.de> wrote:

> Hello,
> I am experimenting with delivering IPv6 multicast traffic over the
> WRT54GS, running OpenWRT. OpenWrt is currently running linux-2.4.30 for
> the mipsel architecture and the OpenWRT distribution has bridged the 4
> port LAN switch (vlan0) with the WLAN interface (eth1) by default.  On
> the IP layer both devices are represented via the br0 interface. The
> bridge work fine for IPv4 Unicast and Multicast and for IPv6 Unicast but
> not for IPv6 multicast.
> I went into a problem with forwarding the MLDv2_report message over the
> bridge from a mobile client, connected over WLAN. The MLDv2 report
> messages are received in in the eth1 (WLAN IF), but not in the eth0 nore
> in the br0 interface. Does the bridge support IPv6 multicast compliant
> MAC addresses, starting with 3333+LowByte(Ipv6 MulticastAddress) ?

The bridge handles IEEE multicast mac addresses 
(ie. least significant bit of first byte of address is set).
What is a an example Ethernet MAC address of a MLDv2 message?

> Usually a bridge is working on L2 and should forward any ICMPv6 packages
> .? The bridge  is forwarding any other IPv6 traffic without problems
> e.g. ICMPv6 messages generated with ping6. MLDv2 report messages are a
> subset of IPv6 ICMP messages with the link local IPv6 multicast address
> FF02::16 ( all MLDv2 compliant router)  as destination address. The same
> behavior I figured out with the MLDv2 query messages, sent by the
> Multicast router to all nodes (FF02::1) on the local link. The MLD query
> I have seen at the eth0  IF but not at the wireless link. Any other IPv6
> link local multicast adresses are forwarded e.g. IPv6 router
> advertisements or neighbour soicitation messages. Do you have any idea,
> how to solve the problem ??

The bridge intentionally knows nothing about higher level protocols.
But if you are using ebtables/iptables perhaps a filtering rule is getting
in the way.

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