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 255.255.252.0.


Sometimes it is observed that the pc s get the ip address from dhcp server but the subnet mask is 255.0.0.0 instead of 255.255.252.0.


Kindly help me in understanding as to why the client subnet mask is 255.0.0.0,

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


will you please post your configuration?


regards

Devang

devang_etcom Sat, 08/19/2006 - 04:19
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ip dhcp database ftp://user:password@172.16.4.253/router-dhcp write-delay 120

ip dhcp excluded-address 172.16.1.100 172.16.1.103

ip dhcp excluded-address 172.16.2.100 172.16.2.103

!

ip dhcp pool 0

network 172.16.0.0 /16

domain-name cisco.com

dns-server 172.16.1.102 172.16.2.102

netbios-name-server 172.16.1.103 172.16.2.103

netbios-node-type h-node


so make sure you have configure right subnetmask


rate this post if it helps


regards

Devang

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


ip dhcp pool PKT

network 10.2.188.0 255.255.252.0

default-router 10.2.188.1

netbios-node-type m-node

dns-server 10.2.188.9


Eventhough the subnet mask is 255.255.252.0 the client takes the ip address but subnetmask as 255.0.0.0.





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


Scott

sundar.palaniappan Sun, 08/20/2006 - 18:59
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Hi,


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!


Regards,

Sundar

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 10.2.188.0 /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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