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Beginner

DHCP Relay Issue, Dropped due to Option 43

I have upgraded a C3750G-12S-E to c3750-ipserviceslmk9-tar.122-55.SE5

This switch is a distribution layer switch for one of my remote sites.  it contains an ip helper-address on the site vlan's SVI.

DHCP relay is no longer functioning for client PCs.  Static address assignment allows full network functionality.

I enabled debug ip dhcp server packet


DHCPD: Looking up binding using address [Correct Network Address]

DHCPD: setting giaddr to [Correct Network Address]

DHCPD: BOOTREQUEST from [Client MAC] forwarded to [Correct DHCP Server IP]

DHCPD: option 43 is malformed (option length 0).

DHCPD: invalid DHCP options - unable to parse

I found this: https://supportforums.cisco.com/message/3151175#3151175 containing:

Actually I am betting you upgraded your IOS from something before 12.2(50)SE to 12.2(50)SE or later.  We added enhancement CSCso19800 which will validate DHCP options when we are a relay agent.

As your option 61 had Leng 0, its invalid and should not be there.

I am using option 43 for LWAPP Discovery and it functions correctly for other sites.  The option contains the IP of my WLC(s).

I currenly do not have any LAPs at this site but will be adding them soon so getting rid of Option 43 is not an option. ( LOL )

Any thoughts?

Your help is much appreciated.

- JK -

3 REPLIES 3
Beginner

DHCP Relay Issue, Dropped due to Option 43

Any suggestions other than downgrading to an earlier version?

I cannot see how this behavior could be "by design"

ajc Frequent Contributor
Frequent Contributor

Re: DHCP Relay Issue, Dropped due to Option 43

Hi,

 

I know this is an old post. did you find a solution for this? I had the same problem this week and temporarily removed the Option 43 from DHCP Scope but that is not a solution as I need it for the AP's to join the right WLC.

ajc Frequent Contributor
Frequent Contributor

Re: DHCP Relay Issue, Dropped due to Option 43

Issue solved after reading the http://www.faqs.org/rfcs/rfc1533.html and removing an incorrect Option 43 configuration from DHCP.

 

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