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HSRP Multicasts Are Flooding My Switchports

Hi

I'm studying for my CCNP Switch exam. I've set up a switch block with

two 3550s and two 2950s. I've also configured HSRP with a 200 msec

hello timer and a & 750 dead timer as per the "Campus Network for High

Availability Design Guide".

Now the PCs that are attached the the access switches are getting

hammered with HSRP messages.

How can I filter these out?

Thx

2 ACCEPTED SOLUTIONS

Accepted Solutions
VIP Purple

HSRP Multicasts Are Flooding My Switchports

HSRP packet woud be sent to Multicast address 224.0.0.2 on udp port 1985. So it is multicast traffic & traverse across trunk links you configured for vlans where HSRP configured. Since you have multiple trunk links between distribution (across access switches & direct distribution switches) traffic can go any path.

In your 2950 switch, is this traffic flooded to all ports (irespective of what vlan configured on it) ? This is a very old switch model & not sure this platform handle multicast traffic exactly the way we wanted.

Following links should help you as well.

Understanding and Troubleshooting HSRP Problems in Catalyst Switch

http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080094afd.shtml

HSRP: Frequently Asked Questions

http://www.cisco.com/en/US/tech/tk648/tk362/technologies_q_and_a_item09186a00800a9679.shtml

Pls rate the response if it is useful

Rasika

HSRP Multicasts Are Flooding My Switchports

Andrew,

You could see if your switch (not all of them do) support "switchport block multicast" on the port. This blocks all multicast though and is not configurable. Otherwise, depending on your setup, you could put your routers in their own vlan and then all of your users in their own vlan.

HTH,
John

*** Please rate all useful posts ***

HTH, John *** Please rate all useful posts ***
6 REPLIES

HSRP Multicasts Are Flooding My Switchports

You can check to make sure that igmp snooping is enabled on the switches. They're generally enabled by default, but may not be on yours.

show ip igmp snooping

HTH,
John

*** Please rate all useful posts ***

HTH, John *** Please rate all useful posts ***
New Member

HSRP Multicasts Are Flooding My Switchports

Hi

I checked the switches. IGMP snooping is enable on all of them.

Unfortunately, it seems IGMP snooping doesn't filter the HSRP multicast

traffic on 224.0.0.2

"In general, addresses from 224.0.0.1 to 224.0.0.255 are reserved... CGMP and IGMP snooping

do not work with this reserved address range."

http://www.cisco.com/en/US/products/hw/switches/ps708/products_tech_note09186a00800b0871.shtml

Andrew

HSRP Multicasts Are Flooding My Switchports

Andrew,

You could see if your switch (not all of them do) support "switchport block multicast" on the port. This blocks all multicast though and is not configurable. Otherwise, depending on your setup, you could put your routers in their own vlan and then all of your users in their own vlan.

HTH,
John

*** Please rate all useful posts ***

HTH, John *** Please rate all useful posts ***
New Member

Re: HSRP Multicasts Are Flooding My Switchports

Hi

There's no joy in HSRP land.

Here's what I've tried:

1. Switchport Block Multicast - This certainly looks good. I tried to configure this on the trunks

at the access layer for multicast traffic entering the switch. Unfortunately, my 2950 switches

don't support this feature.

2. Storm-control Multicast Level 0 - I thought I had it with this one. I configured this on the trunks

at the distribution layer for multicast traffic leaving the switch. Unfortunately, it also filtered the

broadcast traffic.

"...when the multicast traffic rate exceeds the threshold, all incoming traffic, except

spanning-tree packets, INCLUDING BROADCAST AND UNICAST [my emphasis],

is throttled until the level drops below the specified threshold."

http://www.ciscopress.com/articles/article.asp?p=99029&seqNum=3

Conclusion: Don't set aggresive timers without newer equipment. (Switchport Block Multicast looks like the right solution).

Andrew

New Member

Re: HSRP Multicasts Are Flooding My Switchports

I forgot to include my TO DO list...

TO DO: Replace NIC that died under the strain of 2 days worth of 200 msec hello HSRP multicasts

Andrew.

VIP Purple

HSRP Multicasts Are Flooding My Switchports

HSRP packet woud be sent to Multicast address 224.0.0.2 on udp port 1985. So it is multicast traffic & traverse across trunk links you configured for vlans where HSRP configured. Since you have multiple trunk links between distribution (across access switches & direct distribution switches) traffic can go any path.

In your 2950 switch, is this traffic flooded to all ports (irespective of what vlan configured on it) ? This is a very old switch model & not sure this platform handle multicast traffic exactly the way we wanted.

Following links should help you as well.

Understanding and Troubleshooting HSRP Problems in Catalyst Switch

http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080094afd.shtml

HSRP: Frequently Asked Questions

http://www.cisco.com/en/US/tech/tk648/tk362/technologies_q_and_a_item09186a00800a9679.shtml

Pls rate the response if it is useful

Rasika

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