VLANs Multicast Isolation

johnpoz

If you forward multicast traffic from 1 L2 into a different L2... In "theory" that could be used for bad things..

Are you sending it in such a way that all devices on the dest L2 are seeing this traffic, even if they don't need too? Ie didn't join the group. Or have you limited this on your switches acls to only allow the multicast to the device that needs to see this and act upon this traffic?

When you create a boundary, you need to be aware of what can cross that boundary is all.. You would be the only one that can determine if crossing that boundary with traffic X is acceptable to you. A vlan is a boundary, where you can limit what passes between from who to whom..

What I find troublesome in the whole thing is just passing everything to everyone on the other L2.. If that is the case - they might as well just be on the same L2, ie no boundaries. Even if only a discovery method, a compromised system could use it to discover stuff that is different network than itself, and then direct attack to that IP which may or may not be open, etc. etc. I could be used for discovery, that if boundary was in place would not be possible.

This might be an interesting read for you?
https://www.cisco.com/c/en/us/about/security-center/multicast-toolkit.html

Could this be considered over the top for home network - more than likely yes ;) But good security practices are good no matter what the network.

chpalmer

@johnpoz said in VLANs Multicast Isolation:

While I agree in a corp environment I could see a few reasons

Then "never" is the wrong word to use.

We use mulicast for simulcast audio in multi site radio systems. The system is designed to use multicast addresses. We deal in microseconds. .000001 of a second.

Again.. My only issue is the word "Never!" Sometimes it is needed.

johnpoz

@chpalmer said in VLANs Multicast Isolation:

never

Ah your comments are directed at @JKnott but they seem directed at me.. Sorry. I never stated never ;)

chpalmer

@johnpoz said in VLANs Multicast Isolation:

@chpalmer said in VLANs Multicast Isolation:

never

Ah your comments are directed at @JKnott but they seem directed at me.. Sorry.

Still trying to get ahead of this forum software..

johnpoz

So your doing multicast over a wan? I don't see multi sites being over a lan ;) Are you using a tunnel sort of method to connect these sites?

Really don't see how you could be multiple sites, and be worried about microseconds ;)

While sure you can have extended L2s -- this is really a whole different ball of wax when what someone does in their home or even most enterprises.. If you worried about timing at a high level, your going to want minimal "hops" in the wire, etc.. So I would assume where your sending the data would be in some sort of extended L2 where the devices you sending the audio to is in the same L2, you sure and the F are not using avahi ;)

chpalmer

No..noooooo No passing the WAN. Im not sure I saw that idea presented here.

"but I would like to know if on the other two vlan that I have I should block the multicast traffic" I do not see that in the OP's input either..

This is a question as I see it about Multicast between local subnets.

I do it between routers. But no WAN involved.. Totally private networks. But at this point on Cisco routers.

johnpoz

So you have multiple sites radio systems all on the same campus? Just because its some private line doesn't mean its not a wan circuit. How far apart are they sites?

chpalmer

Western part of the state all connected by microwave. Different subnet at all sites. Not my design. but necessary. One of the largest private VOIP networks in the world.

JKnott

@johnpoz said in VLANs Multicast Isolation:

@chpalmer said in VLANs Multicast Isolation:

never

Ah your comments are directed at @JKnott but they seem directed at me.. Sorry. I never stated never ;)

I used "never" when talking about how traffic shouldn't pass between VLANs. I don't recall using it elsewhere, so I'm also not sure what he's referring to.

JKnott

@chpalmer said in VLANs Multicast Isolation:

Western part of the state all connected by microwave. Different subnet at all sites. Not my design. but necessary. One of the largest private VOIP networks in the world.

This is getting confusing. I thought you were talking about a single network where VLANs are used, now it's multiple sites. Also, it's entirely normal to have different subnets between sites. Otherwise you'd need a bridge between sites. It's doable, but that means everything, broadcasts included, can pass over the link. That's generally avoided.

johnpoz

Yeah what he is talking about is this

https://en.wikipedia.org/wiki/Multicast_routing

Completely different ball game to be honest ;) This is NOT what the OP was talking about.. not at all!!