Dhcp server problem in cisco switches / routers.

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Aug 19th, 2006
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We are configuring DHCP server on our L3 switches / Routers in our network. network range is in subnet

Sometimes it is observed that the pc s get the ip address from dhcp server but the subnet mask is instead of

Kindly help me in understanding as to why the client subnet mask is,

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devang_etcom Sat, 08/19/2006 - 04:00
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hi abhay,

will you please post your configuration?



devang_etcom Sat, 08/19/2006 - 04:19
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ip dhcp database ftp://user:password@ write-delay 120

ip dhcp excluded-address

ip dhcp excluded-address


ip dhcp pool 0

network /16

domain-name cisco.com



netbios-node-type h-node

so make sure you have configure right subnetmask

rate this post if it helps



abhayaa123 Sun, 08/20/2006 - 03:19
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Pls find my dhcp configuration

ip dhcp pool PKT



netbios-node-type m-node


Eventhough the subnet mask is the client takes the ip address but subnetmask as

sarbjeet-dhillon Sun, 08/20/2006 - 14:37
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Configuration looks fine.

Try capturing the output from the following the commands whilst doing a dhcp renew.

debug ip dhcp server events

debug ip dhcp server packets

scottmac Sun, 08/20/2006 - 15:18
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Verify that you have "IP CLASSLESS" in your configuration.

For most version of IOS it's on by default, but it's worth checking anyway.

Good Luck


sundar.palaniappan Sun, 08/20/2006 - 18:59
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The router is assigning the natural mask to the clients because it probably ignores the subnet mask you have configured.

Can you make sure there's a space between the IP address and subnet mask in the network statement. You might even want to remove the network statement and reconfigure it.

Hope that helps!



jackyoung Sun, 08/20/2006 - 19:24
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Agreed w/ Scott that the ip classless may be an issue. Moreover, remember to include the "ip dhcp excluded-address " to exclude the gateway & any issue that was statically assigned to the host.

If it still not solve the problem, please post full config and also try to use prefix as below :

ip dhcp pool PKT

network /22

Hope this helps.

abhayaa123 Mon, 08/21/2006 - 04:50
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Thanks for the suggestion,

Will check and revert on this.


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