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Subnet Mask deference

877 views 8 replies 4 participants last post by  zx10guy 
#1 ·
Hi,
I , working as an embedded software developer in the Networking Domain, had a issue in pinging a Device(IP:192.168.1.1 with Gateway of 192.168.1.227 and Mask of 255.255.255.0) from my PC(IP:192.168.2.22 with Gateway of 192.168.2.1 and Mask of 255.255.255.0), but I'm not getting ping response. But Whenever I set my device's(but not my PC) mask to 255.255.0.0 then it is able to pinging. Why class C IP configured device responding when it's mask set to class B's mask 255.255.0.0.
Please Respond me as soon as possible.

Thanks and Regards.,
Siva Prakash Reddy
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#2 ·
Because 255.255.0.0 is larger and includes the other ranges. You need to change your IP to a 192.168.1.x IP to match the rest of the network if you want to use the 255.255.255.0 or if both 192.168.1.x and 192.168.2.x are in use on the network use a 255.255.254.0 mask instead.
 
#4 ·
I didn't see the picture before.

If there is a router or switch in between then there would or should be some routing involved.

You have something labelled as SNMP with an IP, I don't think you have that labelled correctly. SNMP is Simple Network Management Protocol.

You may want to have sit down with your Network admin.
 
#6 ·
Yeah, I had placed routers, which are configured as OSPF, and all are connected to a switch like in attached image. The actual thing is, I tried to test a device in field. But, when i configured my device with subnet mask of 255.255.255.0, it is not responding, While if I configured to 255.255.0.0 it is responding.
Even though I configured two devices with same class-C IPs but why they required for different subnet mask.?
 

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#7 ·
You have the entire set up connected improperly. I don't know what routers you have. What is the IP/subnet you are using to exchange OSPF routes between routers? It can't be the same subnets you've listed as they're not on the same network. You need to stand up another L3 interface on each router which both routers can talk to each other. You can pick something like 192.168.3.x/30. One router would have an IP of 192.168.3.1 and the other would have an IP of .2 with subnet masks of 255.255.255.252. It appears you've never set up a layer 3 network before. If you're going to use OSPF, make sure set up the Area and list the networks you want OSPF to distribute for routes.

Your devices must be connected behind their respective routers being used as their gateways. If that switch you have is a managed switch, you can use that single switch to accomplish connectivity if you're looking for more than one device to be connected to this environment. You'll just logically segment the switch to provide isolated connectivity with VLANs.
 
#9 ·
And you're still not getting what I'm telling you. Your setup is fundamentally wrong from both a layer 2 and layer 3 aspect. I am attaching a diagram showing you how you MUST layout this network for anything to work. It's a very simple layer 3 topology you're looking to set up. If the diagram I'm posting up doesn't make sense to you, you need to stop what you're doing and read up on the fundamentals of layer 2 and 3 before you start messing with doing advanced layer 3 topics such as OSPF routing.
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