troubleshooting Question

Subnet Broadcasting

Avatar of dbrannigan
dbrannigan asked on
NetworkingSwitches / HubsNetwork Analysis
16 Comments1 Solution1139 ViewsLast Modified:
Hi all

This is a rather strange question, but I hope you can help

We have 2 subnets at our office... (FYI they are 10.120.0.0/16 and 10.122.0.0/16) Now these subnets believe it or not exist on the same phyiscal wire.. ie we have two routers each with an ethernet interface in the same switch (on the same VLAN) We also have machines in both subnets plugged into the same switch. The routers are there to obviously "route" between the logical subnets.

The reason for this is complex in which I won't go into much detail..(we want to keep a software licensing server off the 10.120.0.0/16 network and not be visable)

Now heres the question, If I initate a 10.120.255.255 subnet broadcast (from a 10.120.0.0/16 machine) would you expect the 10.122.0.0/16 machines to respond to this? I think that the answer is sort of yes and know. The reason being is that in the IP broadcast packet (at the lower ethernet/data link) level there lies the MAC Address broadcast of FFFFFFFFFFFF. Now all machines WILL pickup this frame (there is no phyiscal seperation of the subnets) Will they respond/visable to the machine who iniated the subnet broadcast? Certainly all machines should respond to 255.255.255.255

I have used network monitor etc to help find out the answer but this is quite vague.
I know there are other solutions to this problem.. ie creating VLAN's and indeed IPSec

Thanks!


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SpazMODic

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