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blackswans
Beginner

Some clients cannot get ip address

Hi,

We are using cisco wlan controller 2504. Some of our clients (laptops, iphones) seems from the wlc that they are getting ip address but from the client it seems to have no ip and no internet access. 

This happens with microsoft dhcp server. If I configure dhcp server on cisco switch wifi works fine and everyone can get ip address. 

Also If I test with other vendow ap with microsoft dhcp it is also working fine. Do you have any idea what is wrong with this wlc?

Regards.

Software Version8.3.143.0

 

5 REPLIES 5
pieterh
VIP Collaborator

Yes,

The wlc has insifficient information to process the request    :-(

 

I mean there are lot of possibilities why this does not work and you need to supply more information.

- Is the AP in local-mode or flexconnect mode?

- is the wlc in dhcp-proxy or in bridging mode?

- does the ap itself get a dhcp address?

- is the dhcp server directly connected to the vlan where the clients reside or do you use multiple vlans?

- do you see any requests in the windows dhcp server logging?

- Is the AP in local-mode or flexconnect mode?

Local mode

- is the wlc in dhcp-proxy or in bridging mode?

- does the ap itself get a dhcp address?

Yes there is no problem with the AP.

- is the dhcp server directly connected to the vlan where the clients reside or do you use multiple vlans?

No I'm using dhcp helper configurations, helpers are configured on L3 switches.

- do you see any requests in the windows dhcp server logging?

Yes I see the requests and also see some DHCP NAK packets.

- Is the AP in local-mode or flexconnect mode?
Local mode

-> the AP passes all DHCP requestst to the WLC and the WLC either

1) handles the request by own dhcp server configuration (I guess this is not configured)

2) performs dhcp-proxy (similar, but not equal to dhcp-relay)

3) just drops the packet on the (v)lan and the packet is forwarded by the ip-helper on the switch

=> please specify more info on the WLC interface configuration.


- is the wlc in dhcp-proxy or in bridging mode?

=> you did not answer this one ?

this is important for the dhcp server return packets,

In proxy mode the wlc uses its management adress to forward the dhcp packets to the dhcp server

can the dhcp server find the route back to the wlc? (I assume for the ip-helper all is configured ok).


- does the ap itself get a dhcp address?
Yes there is no problem with the AP.

=> no further info needed.


- is the dhcp server directly connected to the vlan where the clients reside or do you use multiple vlans?
No I'm using dhcp helper configurations, helpers are configured on L3 switches.
- do you see any requests in the windows dhcp server logging?
Yes I see the requests and also see some DHCP NAK packets.

-> do you have multiple/ dhcp-servers? redundant/failover/load-balancing,

it can mean one offer is accepted and the other recieves a nak. so do not neccessary mean there is a problem.

but can also indicate you've got a rogue dhcp-server on the network?

it could also indicat you've got not enough addresses in the pool, so addresses get exchausted.

=> needs further investigation

 

-> the AP passes all DHCP requestst to the WLC and the WLC either

1) handles the request by own dhcp server configuration (I guess this is not configured)

2) performs dhcp-proxy (similar, but not equal to dhcp-relay)

3) just drops the packet on the (v)lan and the packet is forwarded by the ip-helper on the switch

 

DHCP is microsoft windows server dhcp.

 

=> please specify more info on the WLC interface configuration.


- is the wlc in dhcp-proxy or in bridging mode?

 

Tried with global setting, disabled. Both of them changed nothing. Some phones still dont get ip.

 

=> you did not answer this one ?

this is important for the dhcp server return packets,

In proxy mode the wlc uses its management adress to forward the dhcp packets to the dhcp server

can the dhcp server find the route back to the wlc? (I assume for the ip-helper all is configured ok).

 

Helper is configured on the switch, but I also tried with configuring helper on the wlc interface.

 

 

-> do you have multiple/ dhcp-servers? redundant/failover/load-balancing,

Pool has enough ip addresses. Firstly it was a reduntand server but now we installed a fresh new server but nothing changed.

 

Do you think does it help to take a dump from a client?

 

Thanks.

Best would be to do a pcap on the laptop and the server at the same time. Filter for bootp packets. Please upload an unsuccessful DHCP attempt.
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