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Networking issue

Posted on 2015-01-20
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Last Modified: 2015-01-21
We have a vlan 11 with a DHCP range of 10.11.20.1 - 10.11.254.254 default gateway of 10.11.0.1.

all clients that have an IP address of 10.11.0.x and work fine. All clients that get an IP of 10.11.1.x cannot ping anything (server, gateway, printers, not internet) or be pinged. All client on vlan11 have the same default gateway.

We have a Cisco firewall and cannot find any settings that could be causing this issue. Of course I could be overlooking something.

Not sure if the core switch would do anything. DHCP and DNS are controlled by a windows 2008 DC.

Any ideas?
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Question by:bbayachek
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by:paulmacd
ID: 40559988
What subnet mask are you using?
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by:bbayachek
ID: 40560000
255.255.248.0
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by:bbayachek
ID: 40560009
I think you are on to something. Should we use 255.255.0.0? If so, it is greyed out in the DHCP settings on our windows dc
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by:paulmacd
ID: 40560026
You can't change it, I believe, once you've established the DHCP Scope.  You have to re-create it.
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by:bbayachek
ID: 40560063
that's not going to be fun. Would we use 255.255.0.0?
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by:paulmacd
ID: 40560082
"Would we use 255.255.0.0?"
I can't answer that question for you.  It seems like it would be valid for you, but whether or not it's the best choice...

If creating a new scope is too much trouble, you can create a superscope instead and proceed that way.
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by:bbayachek
ID: 40560142
i just looked at the settings we are using on a IP address calc.

The subnet mask that we are using should be fine. It has a range of 10.11.0.1 - 10.11.7.254
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by:bbayachek
ID: 40560458
ok I found the issue. It was our settings in our core switch. VLAN11 is using subnet mask 255.255.255.0. My new question is if I change the vlan 11 subnet mask to 255.255.248.0 on the core switch would it cause any issues with the devices that are already connected? Will it change the settings in all my other switches?
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Jagrenet earned 250 total points
ID: 40560499
If you change the subnet mask to 255.255.248.0 it should not affect any of the devices that are already connected. When the DHCP lease expires, the devices will get a new IP address with the new subnet mask and connectivity should remain seamless to the end user. Obviously, this means changing the subnet mask in the DHCP scope as well.

Your next question, "Will it change the settings in all my other switches? ". This depends .... are you using VTP (VLAN trunking protocol) in your environment? If so, how is it configured? - (i.e Server, Client or Transparent mode)

How many IP Addresses do you have configured for VLAN11 (on separate SVI's)?
We need a little more info.
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by:paulmacd
paulmacd earned 250 total points
ID: 40561905
"ok I found the issue."
Great!  And as noted, there shouldn't be any consequences to changing the mask.
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