subnet explination

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Jul 10th, 2008
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Saw this configuration on a client and couldn't figure out how this works.


Client configuration:

Address: 10.10.21.26

Mask: 255.255.255.0

Default Gate: 10.25.50.1

With the given subnet mask how does it get to the default gateway on a differient subnet?




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michael.leblanc Thu, 07/10/2008 - 10:46
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If it doesn't have "another" interface on the same network as the default gateway, then the configuration is wrong.

jasosan22 Thu, 07/10/2008 - 11:15
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I am not sure what the router configuration is. I know that the switch(router)Is a 3750 and that it is running VLANS. I know it has a voice and a data.

scottmac Thu, 07/10/2008 - 15:35
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Was there an active VPN?



paul.matthews Fri, 09/05/2008 - 07:35
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This is on a *client*, not a piece of the network? Was the client able to work? Did the client have any other interfaces? VPNs?


Basically if that is the whole story, it should not work, however some (old) clients seem to ignore mask settings. That, combined with the use of proxy arp may let it work anyway.

shane.kearney Fri, 09/05/2008 - 14:34
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Hello, the ip address of 10.10.21.26 /24 has a resident network address of 10.10.21.0 so the first available address is 10.10.21.1 and the last available address is 10.10.21.254 with the broadcast address 10.10.21.255, so any address between 10.10.21.1 and 10.10.21.254 is available and can be used as a default gateway, the whole subnet is 10.10.21.0-255 so the default gateway must reside within this subnet. the configuration above cannot possibly work.

Hope this helps.

mklaphek Tue, 09/09/2008 - 05:25
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I have seen this work IF the client is also using a proxy server (such as Microsoft ISA). In that way, the client, which usually only uses email and web, will go the the ISA server and the gateway won't matter.


Howwver, as others have pointed out, "normal" Layer 3 connectivity isn't possible (or at least shouldn't be!). So, pings should fail, along with other connectivity.

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