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Cisco IOS DHCP server - Handling the receiving of unicasts?

Unanswered Question
Apr 4th, 2006
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Is the Cisco IOS DHCP server capable to handle DHCPDiscover/Requests not as broadcasts but as unicast packets? Is this a configuration issue? Why this question? We test in a Wireless environment the AIRESPACE solution with IOS DHCP server on routers. We found out, that the AIRESPACE controller needs to act as an relay agent (otherwise he doesn't forward these packets). The result is that the DHCPDiscover is correctly converted to an unicast and sent to the IOS DHCP server, but this guy ignores these packets. Note: We need to have the IOS DHCP server running on routers in this environment.

Any ideas? Thanks in advance.


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amit-singh Tue, 04/04/2006 - 23:39
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Yes, Cisco IOS DHCP server can handle the DHCP unicast packets.

Do you have any option in AIRESPACE controller to add the DHCP address.If you have that option make sure that DHCP server IP is there and its enabled.

-amit singh

ak1871 Wed, 04/05/2006 - 00:29
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Hi Amit

I'm not really sure if I understand you correctly. Let me explain the following things: The DHCP server address is already added (to activate the dhcp relay function) on the Airespace controller. But the existing configuration on the IOS dhcp server, which is laying on the router doesn't work for this. Can you explain to me, if possible which parameters are to be added/changed in the configuration? Thanks a lot. -Raffael

amit-singh Wed, 04/05/2006 - 00:37
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Please paste the route configuration.

-amit singh

ak1871 Thu, 04/06/2006 - 00:37
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Hi Amit

Thereby the dhcp part of a router:

ip dhcp pool ACME


domain-name pwlan-acme.com



lease 0 0 15

update arp

accounting DHCP

! *** end ***

Can you tell me which of the config possibilities will solve my problem?:


DHCP pool configuration commands:

accounting Send Accounting Start/Stop messages

bootfile Boot file name

class Specify a DHCP class

client-identifier Client identifier

client-name Client name

default-router Default routers

dns-server DNS servers

domain-name Domain name

exit Exit from DHCP pool configuration mode

hardware-address Client hardware address

host Client IP address and mask

import Programatically importing DHCP option parameters

lease Address lease time

netbios-name-server NetBIOS (WINS) name servers

netbios-node-type NetBIOS node type

network Network number and mask

next-server Next server in boot process

no Negate a command or set its defaults

option Raw DHCP options

origin Configure the origin of the pool

subnet Subnet allocation commands

update Dynamic updates

utilization Configure various utilization parameters

vrf Associate this pool with a VRF


Thank you


ak1871 Tue, 04/11/2006 - 04:17
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It's a long time since I've read/heard about this. So, is it possible to get some input concerning this topic? I'd appreciate to get any updates. Thanks in advance


Bobby Thekkekandam Tue, 04/11/2006 - 05:01
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Hi Raffael,

Do you know for sure if the DHCP server is receiving the DHCP discover frames and whether a DHCP offer is sent?

Try running a debug to verify:

debug ip dhcp server events

debug ip dhcp server packets

This should be safe to run as long as your DHCP clients aren't in the range of thousands or more.

It may be helpful to have a test PC to release/renew so that you can watch for information for that specific machine.



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