[c-nsp] Cisco 7600 multicast traffic - strange behavior

[Chris Evans]

Simple answer is that the group matches up to the link local MAC address
block which is always used for 224.0.0.0/24 groups. Unfortunately the
7600/6500 does the filtering at layer two still, newer platforms typically
do l3 filtering.  Groups x.0.0.0 x.128.0.0 match to the 00-01-5e-00-00-xx
range.  There is a 32:1 overlap on MAC addresses for the mulicast addresses.
These are always flooded. Best practice is to never use these ranges.

Hope this helps.
On Sep 3, 2010 7:26 AM, "Artyom Viklenko" <artem at aws-net.org.ua> wrote:

> Hi, List!
>
> I need some help solving strange problem with multicast
> traffic forwarding.
>
> At the main POP we have 7600 router which connected with
> two TenGig interfaces to the main backbone ring in the
> city. Port Gi3/2 connected to 3560G switch acting as a
> multicast router for IPTV. Several PIM neigbors connected
> to it via vlans passing through 7600 router. Yesterday
> one customer bring up his PIM router and join
> all multicast groups (total of 90 in range of 239.0.0.1
> through 239.0.0.90). This lead to 400Mbit/s traffic from
> 3560G switch through 7600 router in the customer's vlan.
>
> Backbone ring include other 7600 router and several 3750E
> switches. This ring is L2 with MSTP.
>
> Later I found that main 7600 router sends all this multicast
> traffic to all trunk ports containing customer's vlan including
> two TenGig backbone ports and two other GigE ports.
>
> 7600 router runs 12.2(33)SRD4 Adv. IP Services.
>
> Mod Ports Card Type                              Model
> --- ---- -------------------------------------- ------------------
>  1   48  CEF720 48 port 1000mb SFP              WS-X6748-SFP
>  2    8  CEF720 8 port 10GE with DFC            WS-X6708-10GE
>  3   48  CEF720 48 port 10/100/1000mb Ethernet  WS-X6748-GE-TX
>  5    2  Route Switch Processor 720 (Active)    RSP720-3CXL-GE
>
> Also, ip multicast routing switched on and MVPN vrf configured
> on it - have plans to dismiss 3560G as multicast router.
>
> I try to find any glue in Cisco docs and google - no luck.
>
> Is it expected behavior or a bug, or misconfig of something.
> Why router sends multicast traffic to all ports which members
> of customer vlan? There is no igmp joins nor PIM traffic through
> some of these ports.
>
> Please, point me in right direction.
> Thanks!
>
> --
>           Sincerely yours,
>                            Artyom Viklenko.
> -------------------------------------------------------
> artem at aws-net.org.ua | http://www.aws-net.org.ua/~artem
> artem at viklenko.net   | ================================
> FreeBSD: The Power to Serve   -  http://www.freebsd.org
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