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Community Member

Dhcp server problem in cisco switches / routers.

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,

8 REPLIES

Re: Dhcp server problem in cisco switches / routers.

hi abhay,

will you please post your configuration?

regards

Devang

Re: Dhcp server problem in cisco switches / routers.

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

Community Member

Re: Dhcp server problem in cisco switches / routers.

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.

Community Member

Re: Dhcp server problem in cisco switches / routers.

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

Green

Re: Dhcp server problem in cisco switches / routers.

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

Re: Dhcp server problem in cisco switches / routers.

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

Silver

Re: Dhcp server problem in cisco switches / routers.

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.

Community Member

Re: Dhcp server problem in cisco switches / routers.

Thanks for the suggestion,

Will check and revert on this.

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