08-12-2008 10:54 AM - edited 03-06-2019 12:45 AM
I have these two IPs
IP 1---192.168.1.1/24
IP 2-----192.168.2.1 /24
Many thanks
mahesh
Solved! Go to Solution.
08-12-2008 04:41 PM
With all the emphasis on broadcast domains and L2, but since the original question referenced IP subnets, I did want to mention broadcasts themselves are not limited to just L2. For instance, IP can "route" an IP (directed) broadcast to a subnet.
08-12-2008 11:08 AM
Hello Mahesh,
the /24 notation means that the subnet mask is formed by 24 ones followed by 32-24 = 8 zeros
192.168.1.1 255.255.255.0
net part : 192.168.1.0 host part 1
the same for 192.168.2.1/24
192.168.2.1 255.255.255.0
net part : 192.168.2.0 host part 1
net 192.168.1.0 <> net 192.168.2.0
the two ip addresses are in different subnets
a broadcast domain is a layer 2 concept: it is the set of switch ports that receive the same broadcast frame.
the two hosts need a router device cannot talk directly
Hope to help
Giuseppe
08-12-2008 11:35 AM
You can't, unless you now whether the two subnets are virtually or physically separated, and if conneced within a routed environment, how broadcasts are forwarded, or not.
Normally, one would expect two separate subnets would not be within the same broadcast domain, but they can be.
08-12-2008 01:11 PM
Mahesh
I like parts of both responses. I especially like the point that Guiseppe makes that a broadcast domain is a layer 2 concept. And related to that is the point from Joseph that "You can't, unless you now whether the two subnets are virtually or physically separated". To expand on this point a bit: broadcast domains are layer 2 concepts while IP addresses and subnets are layer 3 concepts. You can not look at layer 3 IP addresses and subnets and know for sure what the layer 2 reality is.
As they both sort of say, we make assumptions about relationships between layer 2 and layer 3. One of our assumptions is that a subnet should be its own broadcast domain and when there are 2 separate IP networks there should be 2 separate broadcast domains. But it is quite possible to have a single broadcast domain (perhaps a single VLAN) and to put 2 separate IP networks into it.
It is also true that if you break some assumptions (like the assumption that a subnet should be its own broadcast domain) other assumptions about how things should work (like devices in separate subnets must have a router to communicate) may no longer be true.
HTH
Rick
08-12-2008 04:41 PM
With all the emphasis on broadcast domains and L2, but since the original question referenced IP subnets, I did want to mention broadcasts themselves are not limited to just L2. For instance, IP can "route" an IP (directed) broadcast to a subnet.
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