Networking issue

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?
LVL 1
bbayachekAsked:
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Paul MacDonaldDirector, Information SystemsCommented:
What subnet mask are you using?
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bbayachekAuthor Commented:
255.255.248.0
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bbayachekAuthor Commented:
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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Paul MacDonaldDirector, Information SystemsCommented:
You can't change it, I believe, once you've established the DHCP Scope.  You have to re-create it.
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bbayachekAuthor Commented:
that's not going to be fun. Would we use 255.255.0.0?
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Paul MacDonaldDirector, Information SystemsCommented:
"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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bbayachekAuthor Commented:
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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bbayachekAuthor Commented:
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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JagrenetCommented:
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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Paul MacDonaldDirector, Information SystemsCommented:
"ok I found the issue."
Great!  And as noted, there shouldn't be any consequences to changing the mask.
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