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DHCP problem - all addresses excluded

Hi guys, I seem to have a weird DHCP problem with one of my VLANs. It is a pool of 30 addresses, of which all 30 seem to be excluded! None of them are really excluded with ip dhcp excluded-address command.. Still, show ip dhcp pool shows there are no addresses left. Is there something Im missing?

Range is 172.18.2.129-158. Two shots of the relevant config are attached. Any help would be appreciated!

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16 REPLIES

Re: DHCP problem - all addresses excluded

what subnetmask is being used for the 172.18.2.129 - 158 IPs?

I notice that the address 172.18.2.129 is being excluded yet you say it is not to be excluded?  Are those in the attachment the only addresses that are being excluded or are there more?

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Community Member

DHCP problem - all addresses excluded

255.255.255.224

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Re: DHCP problem - all addresses excluded

Re: DHCP problem - all addresses excluded

from your original post  ----> None of them are really excluded with ip dhcp excluded-address command...

in your second attachement in the original post at the bottom I see ip dhcp excluded-address 172.18.2.129

Are there more excluded addresses than those which you show in the attachement? Is it possible that the rest of the IP addresses have exclude statements in there somewhere?

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Re: DHCP problem - all addresses excluded

The gateway address is the only excluded one. Second attachment in the first post is the list of all excuded addresses, from all VLANs. I first was suspicious that there was a larger IP scope excluded, such as 172.18.1.1-254 for example.. but there is not.

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Re: DHCP problem - all addresses excluded

hi,

first try do lease 1 day in the dhcp pool, also do a show ip dhcp binding and see if any of those ip addresses are there.

Community Member

Re: DHCP problem - all addresses excluded

None of the addresses are leased (show ip dhcp binding). It just keeps getting weirder and weirder..

Lease time is 1 day.

Re: DHCP problem - all addresses excluded

hi milos,

could u try a /24 for your pool?

Community Member

Re: DHCP problem - all addresses excluded

No, network is already designed, and my supervisors would not allow it at this point..

Re: DHCP problem - all addresses excluded

Hi Milos,

What are the masks for the other subnets of 172.18.2.x?

Best regards,

Alex

Community Member

Re: DHCP problem - all addresses excluded

Hey Alex, thanks for trying to help. Other 172.18.2.x subnets are:

172.18.2.32 /27

172.18.2.0 /27

172.18.2.64 /26

172.18.2.128 /27

Re: DHCP problem - all addresses excluded

Maybe all clients in this subnet booted at the same time? 

This could lead to dhcp issues, we once had an issue with a lot of access points all booting up at the same time leading to this issue, exhausting the dhcp addresses while in fact there were enough adresses in the pool , but still...

We solved this by clearing dhcp and then booted the aps (clients) at different moments in time.

Good luck.

Community Member

Re: DHCP problem - all addresses excluded

Subnet clients are all workstations..

Re: DHCP problem - all addresses excluded

Hi Milos,

You can have a problem because network 172.18.2.64 /26 is with lower prefix then the previous networks 172.18.2.0 /27 and 172.18.2.32 /27. You have already divided 172.18.2.0 into /27 networks you cannot assign /26 network in the middle only at the beginning.

Best regards,

Alex

EDIT: More info on VLSM:

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800a67f5.shtml

http://www.cisco.com/web/learning/netacad/demos/CCNA3v3Demo/ch1/1_1_4/index.html

Community Member

Re: DHCP problem - all addresses excluded

Could it be that it is Subnetting 101?! I will have to convince my superiors to try changing the scope. Thanks in advance for all of you who chipped in!

Re: DHCP problem - all addresses excluded

Yes it could be. You should revise your IP addressing and subnetting in this network. It can have hierarchy but it is done when you have your smaller networks (higher perfix) after the bigger networks (lower prefix). Otherwise you can have a lot of unpredictable outputs.

Best regards,

Alex

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