Question about DHCP Bindings

Unanswered Question
Jul 19th, 2009

Hi All,

I'm seeing some strange DHCP bindings on our router.

core2#sh ip dhcp binding

IP address Client-ID/ Lease expiration Type

Hardware address

172.16.75.111 0065 Jul 21 2009 02:54 PM Automatic

172.16.75.112 0100.2608.e469.17 Jul 21 2009 02:06 PM Automatic

172.16.75.113 0021.e9a0.777c Infinite Automatic

DHCP config:

ip dhcp pool Wireless-512b

network 172.16.75.0 255.255.255.0

domain-name netspace.net.au

default-router 172.16.75.1

dns-server 210.15.254.240 210.15.254.241

What I don't understand is:

1/ Why is one DHCP client able to obtain an "Infinite" lease? I haven't set the lease option in the dhcp config and it should default to just 1 day. But there's this one DHCP client that keeps getting an infinite lease.

2/ How can one set the Client-ID/Hardware address to something other than the mac address? In the example we're getting a DHCP request from a Client-ID with 0065 - how is this possible???

Thanks.

Andy

I have this problem too.
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pidoshi Tue, 07/21/2009 - 00:06

Hi Andy,

To answer for #1, it seems that you'r receiving a request from a BOOTP client, you might wanna check RFC1534 for the expected behavior of Infinite lease for a BOOTP client. As a solution you might wanna let the client use DHCP instead if that's possible or ignore BOOTP request on the router using "ip dhcp bootp ignore"

For #2 - Its Implementation specific, i mean it ideally depends whether the Client has the capability to insert DHCP Option 61 as part of the DHCP Discover/request packets..

cheers

Pinku

asaykao73 Tue, 07/21/2009 - 00:10

Thanks Pinku.

1/ "ip dhcp bootp ignore" is not supported on the 7606, so will just have to live with this infinite lease for now.

2/ you are correct, looks to be implementation specific with the client being able to utilize option 61.

Cheers.

Andy

asaykao73 Tue, 07/21/2009 - 00:19

Running Version 12.2(18)SXF11

core2(config)#ip dhcp ?

conflict DHCP address conflict parameters

database Configure DHCP database agents

excluded-address Prevent DHCP from assigning certain addresses

limited-broadcast-address Use all 1's broadcast address

ping Specify ping parameters used by DHCP

pool Configure DHCP address pools

relay DHCP relay agent parameters

route Specify the type of routes for clients on unnumbered interfaces

smart-relay Enable Smart Relay feature

snooping DHCP Snooping

asaykao73 Tue, 07/21/2009 - 00:22

There is the option to use "no ip bootp server".

When I enable this command and clear the DHCP bindings, the client still gets on with an infinite lease. Seems to have no impact.

172.16.75.119 0021.e9a0.777c Infinite Automatic

pidoshi Tue, 07/21/2009 - 01:15

I don't think so disabling "bootp server" will work. It seems the later 12.2SR codebase has the option for disabling BOOTP request via "ip dhcp bootp ignore" CLI..

cheers

Pinku

asaykao73 Tue, 07/21/2009 - 21:36

Hi Pinku,

We'll live with it for now :)

Thanks for your help.

Cheers.

Andy

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