L2 communication between different network segments

[vandermause]

Is it possible to communicate between two different network segments within a single vlan? Both devices on VLAN1, untagged.  10.9.10.10/24 communicating with 192.168.1.33/24 via layer two communication.  Is this possible?

Just to clarify a bit further, I don't think this would be advisable, but would it work?  Just curious if anyone has seen or lab tested a scenario like this before.

[FredrikB-NN2]

SephenW's reply is the _correct_ way to do it, but that makes it L3, routed. Let's go back one step. Ethernet is supposed to communicate within Ethernet segments, so that will of course work. As you indicate that you want hosts with IP addresses to communicate, that is NOT via Ethernet, but via IP. Now, on a local IP subnet, the IP traffic may be (and is very often these days) carried in Ethernet frames. This IP traffic is then limited by the rules for IP communication and saying that a host on 10.9.10.0/24 should talk L2 to something on 192.168.1.0/24 just makes no sense.

Then again, if those hosts also have another type of communication, besides IP, they may well do that over L2, like IPX, Appletalk or some proprietary protocol. To make things even more complex, they could have a third set of IP addresses, say 10.255.255.0/24, that is shared among them. Within that subnet, L2 is possible.

[vandermause]

Thank you for your reply @FredrikB-NN2.  I completely agree that this just makes no sense.  It is not really that I want it this way, but more that this situation does exist in our environment, and I am trying to understand how it is.  Thank you for the other protocols that you mentioned.  This will be something I can look into as a possible culprit.  I was primarily focused on L2 and L3 in the TCP/IP stack.  I am also new to the company and will be investigating the possibility that I haven't collected all data yet.  Thank you for your help!

[StephenW · Accepted solution]

The switch would have to be the router for both network segments.  It does work, but as you said... not advisable.

configure vlan Default ipaddress 10.9.10.10/24
configure vlan Default add secondary-ipaddress 192.168.1.33/24
enable ipforwarding vlan Default

[vandermause]

@StephenW - I believe you are referring to Multinetting, correct?

ExtremeXOS® Command Reference Guide (extremenetworks.com)

After reading a bit on mulitnetting, I agree completely that this would not be advisable.  This seems more like a short term remedy, rather than any long term solution.  I plan on collecting more information from the team and seeing what we can do to split the broadcast domains into their own VLANs and establish a better IP Schema.  Thanks for your reply and insight to my question.