Multicast Routing on a Cicso 3750

Posted on 2009-04-29
Medium Priority
Last Modified: 2012-05-06
I've got a Cisco 3750 switch/router, first line of show version reports:

Cisco IOS Software, C3750 Software (C3750-IPSERVICES-M), Version 12.2(35)SE5, RELEASE SOFTWARE (fc1)

Ive got 3 VLANs 1, 100 and 200. I want each VLAN to act like a regular switch with respect to multicast traffic. Meaning its a broadcast until it hits the router. I also need the multicast to be routed between the VLANs as different applications on those VLAN subscribe for them. So, I turned on PIM with the following commands:

ip multicast-routing distributed

And on each VLAN interface:

ip pim sparse-dense-mode

I couldnt just enter ip multicast-routing. It told me that was an incomplete command. So now multicast packets only go to ports on the VLAN where apps have subscribed. I would like to turn off the smarts controlling the VLAN multicast traffic but keep automatic multicast routing on. How do I do that?

Question by:MassiveD
  • 4
  • 2

Expert Comment

ID: 24265503
I think you did it correctly, here's a recap for each VLAN interface:
interface interface-id
ip pim version 2
ip pim sparse-dense-mode
show run
copy run start
Your VLAN's all have IP's assigned right?

Author Comment

ID: 24275072
I didn't have the ip pim version line. I have added it. The switch doesn't support version 2, so I turned on version 1. That didn't fix my problem.

I have IP addresses assigned to each VLAN. I have ip routing enabled and unicast routing is working fine.

I've got 2 devices on 2 ports of a single VLAN. Each one is sending out multicast traffic on One is using UDP destination port 11841 and the other is using port 11842. Neither device actually subscribes for that multicast address. As a result, neither one can see the others multicast traffic.

My understanding of VLANs is that they are like logical switches. When I use a simple linksys switch, each app can see the other ones traffic fine. I think the cisco switch is doing multicast routing on the VLAN. So the multicast packets only go to the ports that have subscribed. I need the VLAN to be more like a regular switch. I also need to keep the ability to dynamically route multicast traffic across the VLANS.

Expert Comment

ID: 24281177
If you are unable to issue the command ip multicast-routing globally to enable it, then you probably are not running advanced feature set on that switch. Find it and download it.
It is called Advanced IP Services with Web Based Device Manager
the filename is c3750-advipservicesk9-tar.122-40.SE.tar
Just make sure your switch has at least 128MB DRAM and 16MB Flash memory.
With this feature set, you can enable the multicast-routing globally without having to setup subscriptions. You will still have to have ip pim sparse-dense-mode enabled for each VLAN.
Independent Software Vendors: We Want Your Opinion

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!


Author Comment

ID: 24300722
That file can't be installed. It says I don't have the correct feature set.

I can issue to following command to globally enable multicast routing:

ip multicast-routing distributed

The problem is, that seems to effect how multicast is treated on the VLAN level too. All the applications get their multicast traffic when they join the multicast group. I've got 1 app that doesn't join a group. It relies on the VLAN to broadcast multicast traffic. This switch doesn't seem to do that once multicast routing is enabled. If the app doesn't subscribe, it doesn't get the data, even though it's on the same VLAN as the sender. That's what I am trying to fix.

Author Comment

ID: 24338170
Any other ideas?

Accepted Solution

MassiveD earned 0 total points
ID: 24399967
I figured it out. I had to turn off IGMP snooping like this

no ip igmp snooping

Featured Post

Free Tool: SSL Checker

Scans your site and returns information about your SSL implementation and certificate. Helpful for debugging and validating your SSL configuration.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

New Server  was moved from behind Router R2 f0/1 to behind router R1 int f/01 and has now address But we want users still to be able to connected to it by old IP. How to do it ? We can used destination NAT (DNAT).  In DNAT…
How to set-up an On Demand, IPSec, Site to SIte, VPN from a Draytek Vigor Router to a Cyberoam UTM Appliance. A concise guide to the settings required on both devices
After creating this article (http://www.experts-exchange.com/articles/23699/Setup-Mikrotik-routers-with-OSPF.html), I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…
After creating this article (http://www.experts-exchange.com/articles/23699/Setup-Mikrotik-routers-with-OSPF.html), I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…

809 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question