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New Member

Multicast

I'm fairly new to IP Multicast. I've been reading up on it and it is getting harder and harder to grasp. I have a Cisco 4506 running as my core switch. It is doing all my inter vlan routing. It is the only router on our LAN. I have about 30 other edge switches. about 30 vlans total with roughly 800 hosts. I inherited this network and at first everything was running on vlan 1. Now i have segmented it a little but there is still about 50% of the hosts on vlan 1. I'm trying to configure multicast on our network. I first realized i needed multicast when our Ghost stopped working. I have enabled IP Multicast-routing, igmp snooping is enabled, Loopback interface on 4506 is the RP, IP PIM Sparse-mode on necessary vlans. When i turn on IP Pim SM on a vlan other than vlan 1, the CPU is fine. But when i enable it on vlan 1, the cpu stays at 80-90%. It eventually drops to around 70 but it spikes. I know vlan 1 is the problem, but i want to know if i have configured multicast right. Like i said, all of this is on my 4506. Also, when i run SHOW IP IGMP GROUPS, i get a huge list of groups. A lot of printers, servers, and weird things like our proximity panels. any ideas?

13 REPLIES

Re: Multicast

I'am at the same level as you are. Fortunately you got a problem which will help understand things better. But as per theory, IGMP snooping sniff's every multicast pkt to knw the information. This may be adding to the cpu load. so may changing it to IGMP ver may hlp.

Lets see what experts have to say. This definitely is a great learning topic.

New Member

Re: Multicast

thanks. This is really an important issue. any suggestions will be great!

New Member

Re: Multicast

anyone?

Re: Multicast

I think ur issue is caused by combination of igmp snooping + huge number of groups.

igmp snooping is useful, so we need to question the huge nuymber of groups.

if you know hich groups you need to carry, you coudl have an IGMP static join, with class map on upsteream interface configured for PIM. this way you will reduce ur groups.

How many are they anyway ?

Sam

New Member

Re: Multicast

On vlan 1 there are about 25 groups. On some of the others there are around 5. One thing i noticed is a lot of printers. AV equipment and proximity panels. why would devices like this be using multicast?

Re: Multicast

25 groups shopudl not cause any issues, I have 75 multicast groups for IPTV on 7600 + 4500 and all is working as it should. baselined at 40% CPU.

1-what do u get out of "sh processes cpu | exc 0.00" ?

2-do u have to use VLAN 1 ?, try usng another VLAN and limit it to ports were feed is required.

3-how is multicast carried, within VLANs through 4506 or routed by 4506 in global routing table.

Sam

Bronze

Re: Multicast

There's also a nice document that goes through some methods for troubleshooting high CPU usage on the 4500 series switches:

http://www.cisco.com/en/US/products/hw/switches/ps663/products_tech_note09186a00804cef15.shtml

Silver

Re: Multicast

Hi,

could you send the vlan 1 configuration? And your topology?

thanks

Andrea

New Member

Re: Multicast

!

interface Vlan1

description Data

ip address 10.0.0.1 255.255.248.0

ip pim sparse-mode

!

(I had nothing to do with the /21 on vlan 1)

it is a 4506, with about 30 vlans. it is doing my interklan routing. we have about 800 hosts total in the network with about 500 still on vlan 1. i'm trying to segment as fast as possible.

New Member

Re: Multicast

With NO Multicast on vlan 1

Admin_4506#sh processes cpu | exc 0.00

CPU utilization for five seconds: 21%/3%; one minute: 26%; five minutes: 30%

PID Runtime(ms) Invoked uSecs 5Sec 1Min 5Min TTY Process

16 41821524 146736251 285 0.23% 0.17% 0.20% 0 ARP Input

27 24606609763580494840 687 9.59% 11.24% 11.32% 0 Cat4k Mgmt HiPri

28 28814752363591023803 802 6.95% 11.32% 14.65% 0 Cat4k Mgmt LoPri

38 84011412 143613165 584 0.39% 0.54% 0.51% 0 Spanning Tree

44 69394348 463932950 149 0.23% 0.21% 0.21% 0 IP Input

50 2975080 15860645 187 0.07% 0.06% 0.05% 0 CEF process

Multicast on

Admin_4506#sh processes cpu | exc 0.00

CPU utilization for five seconds: 85%/4%; one minute: 31%; five minutes: 30%

PID Runtime(ms) Invoked uSecs 5Sec 1Min 5Min TTY Process

16 41821612 146736543 285 0.07% 0.16% 0.19% 0 ARP Input

27 24606674483580512889 687 5.59% 11.04% 11.29% 0 Cat4k Mgmt HiPri

28 28814863643591037951 802 68.71% 16.06% 14.91% 0 Cat4k Mgmt LoPri

38 84011668 143613249 584 0.39% 0.48% 0.50% 0 Spanning Tree

44 69395072 463937574 149 3.91% 0.59% 0.29% 0 IP Input

50 2975104 15860791 187 0.15% 0.05% 0.05% 0 CEF process

53 393092 2368304 165 0.31% 0.08% 0.01% 0 IGMPSN

92 97524 586142 166 0.07% 0.05% 0.01% 0 IGMP Input

98 335756 7443704 45 0.07% 0.02% 0.02% 0 IP-EIGRP(0): HEL

99 324 318 1018 1.75% 0.25% 0.05% 2 Virtual Exec

New Member

Re: Multicast

my 4506 is doing intervlan routing. Some clients are in other vlans. I have about 500 hosts on vlan 1. I'm trying to break it up but that is A LOT of stuff on vlan 1.

Hall of Fame Super Bronze

Re: Multicast

28 28814863643591037951 802 68.71% 16.06% 14.91% 0 Cat4k Mgmt LoPri

It sounds like you have a rogue multicast client in your network. This client is sending a lot of IGMP joins/leaves which is affecting the IGMP Snooping in the switch.

I suggest you to take a packet trace to determine which device is causing this.

HTH,

__

Edison.

New Member

Re: Multicast

10-4

I think i know what it is but i can't take him off the network yet.

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