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Community Member

InterVLAN routing and broadcasts

I have a multi vlan environment w/ intervlan routing enabled so that hosts in both vlan's can talk. The problem that I am having is that there is a projector in vlan x that the PC's in vlan y need to use. The projector software broadcasts to find the projectors, but I'm not sure what type of broadcast. The problem is that the broadcasts don't traverse the svi's (as they shouldn't) but I need them to. I am sure there is a simple command to do this, but I don't know what it is.


Re: InterVLAN routing and broadcasts

I am not familiar with the projector software, however you may be running into an issue where you need to add an IP HELPER ADDRESS statement on the interface that has the PC's on it. This will pass certain broadcast protocols to the server (in your case the projector). Try that ...

Re: InterVLAN routing and broadcasts

Find out what port number the projector uses and maybe you can use ip helper with ip forward protocol, also find out if it's multicast.

Re: InterVLAN routing and broadcasts

Just adding to Bosalaza post.

check more information on the link:

As a last resource:

ip forward-protocol any-local-broadcast

To forward any broadcasts including local subnet broadcasts, use the ip forward-protocol any-local-broadcast global configuration command. To disable this type of forwarding, use the no form of this command.

(not sure if this is still in use)



Community Member

Re: InterVLAN routing and broadcasts

OK - I will try that. Just one quick question...

Which interface do I want to put that command on? If you look at the attached image, VLAN X is the PC that has a dfgw of, so would that router's E0 int get the helper command? Or would I put in on the SVI for VLAN X? I shouldn't need to do anything with VLAN Y, should I?

Thanks for all of your assistance!

Re: InterVLAN routing and broadcasts

you would add the helper-address on the interface where you believe origin of the braodcast needs to be translated to, for example, the broadcast is coming from vlan 1 and that broadcast needs to be directed to vlan 2, so in interface vlan 1 you would have "ip helper-address vlan2.255". One more thing, I do not believe the video feed is using broacast to send it's stream to other clients that need that feed, it is probably using multicast, if it is indeed using broadcast, its poorly designed, as broadcast would use up all available b/w and eveyone will hear that broadcast even the ones that do not ask for it. my .02 cents.


Community Member

Re: InterVLAN routing and broadcasts

These projectors are not using the broadcast for video. It is just the software locating the projector. The software allows for me to put in an IP address, and then it will work fine, but the end users won't want to put in an IP address every time they want to use these projectors. If it's on the same vlan, the software will immediately locate all projectors on that vlan, but not the ones in any other vlan. That is why I think that it's a broadcast. The actual video doesn't have a problem.

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