Cisco 4006 Layer2 Multicast forwarding problem

[l-gu]

Layer2 multicast forwarding happens between four FE ports on Cisco 4006 switch, and all multicast packets pass through CPU of Cisco 4006, and it lead to very high CPU utilization on Cisco 4006.

Cisco 4006 IOS version 12.1(19)EW

!

ip multicast-routing

!

int Vlan x

ip address x.x.x.x

ip pim spare-dense-mode

!

# all four FE ports belong to the VLAN.

And inject traffic is 5 Mb/s by IXIA

[Georg Pauwen]

Hello,

you might want to try and enable fast switching of multicast packets using the ip mroute-cache interface configuration command. Fast switching of multicast packets is off by default, so turning it on might decrease CPU utilization:

interface VLAN x

ip mroute-cache

HTH,

Georg

[Steve Fuller]

The other thing to consider here is the IP multicast group address you are sending the traffic into.

I know in the Cat6K there are a number of control plane group MAC addresses as follows:

01-00-5e-00-00-01 General Query

01-00-5e-00-00-04 DVMRP

01-00-5e-00-00-05 MOSPF

01-00-5e-00-00-06 MOSPF

01-00-5e-00-00-0d PIMV2

01-00-5e-00-00-13 RGMP

Any traffic destined to these group MAC addresses als gets sent to the CPU.

Although you may not be using one of the above addresses, due to the 32:1 address overlap within IP multicast MAC addresses, if the group address you are using is the same as one of the above, this traffic will also be sent to the CPU for processing.

Check the IP Multicast Group Troubleshooting guide (http://www.cisco.com/en/US/partner/tech/tk828/tk363/technologies_tech_note09186a0080094b55.shtml#groupaddresses) for further info on the address overlap.

[l-gu]

Thanks for your reply.

here's more information:

Multicast address: 239.255.154.26

Run time: 5 mins 30 seconds

Default Multicast TTL: 10

Inject traffic: 5Mb/s

CPU utilization reach to 99%

Below is layer2 forwarding table about MAC address:

#show mac-address-table multicast vlan 7

Multicast Entries

vlan mac address type ports

-------+---------------+-------+-------------------------------------------

7 0100.5e7f.0001 igmp Switch,Fa6/47

7 0100.5e7f.000d igmp Switch,Fa6/47

7 0100.5e7f.0015 igmp Switch,Fa6/47

7 0100.5e7f.9a1a igmp Switch,Fa6/26,Fa6/27,Fa6/28

7 ffff.ffff.ffff system Switch,Fa6/25,Fa6/26,Fa6/27,Fa6/28,Fa6/47

I found the last multicast MAC address ffff.ffff.ffff is very strange; on cisco 3550/6509 I can't see.

But

!

no ip igmp snooping

!

mac-address-table static 0100.5e7f.9a1a vlan 7 interface Fa6/26 Fa6/27 Fa6/28

!

# here we disable ip igmp snooping, and add static multicast MAC.

All multicast packet won't be forwarded to CPU.

Why?

[l-gu]

I resolve the problem, multicast packet with TTL =0 or 1 will lead to high CPU utilization.