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DHCP problem - all addresses excluded

Unanswered Question
Nov 1st, 2011
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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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Marius Gunnerud Tue, 11/01/2011 - 02:01
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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?

fearless.rabbit Tue, 11/01/2011 - 02:10
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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.

Ionut.Hristea Tue, 11/01/2011 - 02:48
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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.

fearless.rabbit Tue, 11/01/2011 - 02:56
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None of the addresses are leased (show ip dhcp binding). It just keeps getting weirder and weirder..


Lease time is 1 day.

johnlloyd_13 Tue, 11/01/2011 - 03:44
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hi milos,


could u try a /24 for your pool?

fearless.rabbit Tue, 11/01/2011 - 05:41
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No, network is already designed, and my supervisors would not allow it at this point..

Alexander Maroukian Tue, 11/01/2011 - 04:18
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Hi Milos,


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


Best regards,

Alex

fearless.rabbit Tue, 11/01/2011 - 05:44
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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

Ton V Engelen Tue, 11/01/2011 - 06:13
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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.

Alexander Maroukian Tue, 11/01/2011 - 06:27
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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

fearless.rabbit Tue, 11/01/2011 - 09:08
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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!

Alexander Maroukian Tue, 11/01/2011 - 10:27
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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

Marius Gunnerud Tue, 11/01/2011 - 01:48
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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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