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New Member

Problems with obtaining IP addresses

I have had our WLC4400 in place for around five years.  No configuration changes have been made to it or the 32 LWAPPs connecting to it.  We have begun to have some spotty issues with client devices.  The error message says they are unable to obtain an IP address.  After they wait a few minutes, they connect.  We have plenty of DHCP addresses available.  We have 25 locations with at least one AP and the problem seems to be system wide.  One person can connect and the person beside them cannot.  Many say they have been connecting to our library wireless for a long time with no problems.  No error messages are being logged.

Thanks for any help or ideas you can provide.

17 REPLIES
Cisco Employee

Problems with obtaining IP addresses

Hello,

What version of code is running on your WLC?

The next step would be to grab a client debug for a device that cannot get DHCP (are these APs in local mode or H-reap mode?)

On the WLC command line:

debug client xx:xx:xx:xx:xx:xx (mac addr of client device)

-Pat

New Member

Re: Problems with obtaining IP addresses

Thanks for responding. I have answered your questions below.

Cisco Employee

Re: Problems with obtaining IP addresses

I think you may have accidently left off your answers/debugs from your previous post.

-Pat

New Member

Re: Problems with obtaining IP addresses

We have had to put the wireless troubleshooting on the back burner until today. We learned two things; Initially, the client receives the auto-configuration IP in Windows (169.x.x.x) The WLC is handing out 10.13.x.x addresses. When you do an IP Renew, you are given a working IP. Using the debug client command on the WLC shows me it is trying to hand out 0.0.0.0:

Fri Feb 24 14:20:54 2012: DhcpProxy(): Setting dhcp server from OFFER server: 10

.1.1.200

client mac: 00:c6:10:32:84:57 offer ip: 0.0.0.0

Do you have any idea as to why this would be happening?

Thank you,

Anna Turner

IT Manager

Tulsa City-County Library

Work - 918.549.7301

Cell – 918.607.1422

Cisco Employee

Re: Problems with obtaining IP addresses

Hi Anna,

I would need to take a look at a full client debug  from the start of the connection for more clues. Also, what version of  code are you running on the WLC?

Also, if I could see your interface configuration for the WLAN in question (and the management interface details):

show interface detailed management

show interface detailed

If you do not want to post this information publically, you can send it in a private message and I will try to take a look.

-Pat

Bronze

Re: Problems with obtaining IP addresses

Anna,

You are not really clear on what device is handing out the IP addresses. Is it the WLC or an external server. If it is the WLC, then all your clients should experience the same problem, and if this is the case, then make sure DHCP proxy is enabled under  Controller -> Advanced->Dhcp. If you are using an external DHCP server, and running HREAP, then check the vlan mapping on the access points to make sure the vlan for clients are correct

New Member

Re: Problems with obtaining IP addresses

It is the WLC doing DHCP. It has been up for years and working flawlessly until several months ago. No changes in the configuration have been made, either. When on a client that wasn’t connected, I clicked the wireless icon in the task bar and it connected. No particular devices are problematic, clients connected previously have problems but most do not. I haven’t experienced it yet on my three wireless devices. We have 37 APs throughout the system and all the locations seem to be experiencing the issue so it has to be the WLC. What else can I provide?

Version 4.1.171.0

(Cisco Controller)

User: root

Password:********

(Cisco Controller) >show interface detailed management

Interface Name................................... management

MAC Address...................................... 00:18:b9:ea:a3:40

IP Address....................................... 10.1.1.200

IP Netmask....................................... 255.255.0.0

IP Gateway....................................... 10.1.1.1

VLAN............................................. 100

Active Physical Port............................. LAG (29)

Primary Physical Port............................ LAG (29)

Backup Physical Port............................. Unconfigured

Primary DHCP Server.............................. 10.1.200.1

Secondary DHCP Server............................ Unconfigured

DHCP Option 82................................... Disabled

ACL.............................................. Unconfigured

AP Manager....................................... No

(Cisco Controller) >

Again, thank you!

Anna Turner

Bronze

Re: Problems with obtaining IP addresses

On the Advanced tab in the WLAN config, do you have dhcp required ticked. If so could you check if the clients with the problem have static ip in the wireless properties. Also your WLC code is old. Could you upgrade to version 7. What service packs are the laptops running

Sent from my HTC

Cisco Employee

Re: Problems with obtaining IP addresses

Hi Anna,

Alright, one idea comes to my mind, we did have a bug in earlier 4.x WLC code:

CSCsy79782: WLC uptime reset to 0 after being up for 497 days.

Basically, counters WLC could reset if it was up for 497 consecutive days. The results after these counter resets are unpredictable, and intermittent issues can result.

A code upgrade on the WLC should be considered if possible, but what is the current Uptime on your WLC? You might want to simply try a WLC reboot during a maintenance window if the above condition could be possible.

Otherwise, if you can capture a full client debug of a failure we can take a look.

-Pat

New Member

Re: Problems with obtaining IP addresses

My understanding is that the WLC was never intended to be a DHCP server for clients, only for APs, which is why you can't set other DHCP options other the the regular def gateway and DNS

By default the WLC is set to "enable DHCP Proxy" a.k.a. DHCP Relay

When a client connects to an SSID they are associated to a VLAN and you can specify the external DHCP in the advanced tab of the WLAN setup, or on the interface, if set. If you want to use a DHCP server or IP Helper without relaying through the WLC then you'll need to disable the DHCP Proxy so that DHCP Offer broadcasts are sent directly out the interface.

I think the fact that it worked originally might have just been good luck, as it will depend on the VLAN that you were using and adding more VLANs / Interfaces would likely upset this

That's my understanding anyway

Sent from Cisco Technical Support iPad App

New Member

Re: Problems with obtaining IP addresses

This all started a month or two after we moved to a new Layer 3 switch. Even though the interface the WLC is plugged into appears to be the same – vlan 100 and vlan 105, perhaps there is a default setting confusing the dhcp requests. I shouldn’t need a helper address, since there is no actual broadcast within our network. The WLC intercepts the request but I was told it was meant to be a DHCP server for clients. If not, it worked well for us for years, thankfully!

I truly appreciate everyone’s help on this. I have an engineer coming tomorrow who may be able to help me with the new switch configuration, if that is indeed my problem.

Bronze

Re: Problems with obtaining IP addresses

Hi Anna,

You have shed more light by mentioning the L3 switch. I also noticed that your DHCP server is 10.1.200.1, while your WLC management IP is 10.1.1.200.

Firstly, the disparity in IP means that the WLC is not the dhcp server. If it was, then the dhcp server IP address would be same as the dhcp management IP.

Secondly,  if VLAN 100 is for WLC management IP and VLAN 105 is for the AP manager interface, then you have to be able to route between VLANs via the L3 switch by configuring Switched Virtual Interfaces on the Layer 3 switch.

Thirdly, if you actually have an external dhcp server, then you must put an IP helper address on VLAN 105  on the L3 switch.

New Member

Re: Problems with obtaining IP addresses

I do have the management IP, 10.1.1.200, which is the local network. All DHCP requests are handled by the WLC. There is no active DHCP server on 10.1.200.1. I will see if I can find that in the config somewhere. I don’t think that is being used, though.

Here is a sample from our layer 3 switch:

11:59:04.996636 In 00:24:d2:3f:2b:91 > ff:ff:ff:ff:ff:ff, ethertype 802.1Q (0x8100), length 64: vlan 105 , p 0, ethertype ARP, arp who-has 169.254.44.56 tell 0.0.0.0

Listening on ge-0/0/47, capture size 96 bytes

12:00:42.154631 Out 2c:21:72:9d:6a:32 > 01:80:c2:00:00:0e, ethertype LLDP (0x88cc), length 74: LLDP, name GATEWAY, length 60

12:00:42.511716 In 5c:59:48:e3:32:62 > 01:00:5e:00:00:16, ethertype 802.1Q (0x8100), length 64: vlan 105, p 0, ethertype IPv4, 169.254.74.139 > 224.0.0.22: igmp v3 report, 1 group record(s)

12:00:43.038075 In f0:cb:a1:6f:eb:38 > 01:00:5e:00:00:fb, ethertype 802.1Q (0x8100), length 74: vlan 105, p 0, ethertype IPv4, truncated-ip - 98 bytes missing! 10.13.3.98.5353 > 224.0.0.251.5353: 0 [|domain]

12:00:43.667016 In 18:34:51:f0:6c:61 > 2c:21:72:9d:6a:01, ethertype 802.1Q (0x8100), length 64: vlan 105, p 0, ethertype ARP, arp who-has 10.13.0.1 tell 10.13.2.149

12:00:43.667143 Out 2c:21:72:9d:6a:01 > 18:34:51:f0:6c:61, ethertype 802.1Q (0x8100), length 46: vlan 105, p 0, ethertype ARP, arp reply 10.13.0.1 is-at 2c:21:72:9d:6a:01

12:00:43.997231 In d0:df:9a:80:d0:c0 > 2c:21:72:9d:6a:01, ethertype 802.1Q (0x8100), length 74: vlan 105, p 0, ethertype IPv4, truncated-ip - 24 bytes missing! 10.13.2.205.63192 > 192.168.1.5.51602: UDP, length 52

12:00:43.997344 Out 2c:21:72:9d:6a:01 > d0:df:9a:80:d0:c0, ethertype 802.1Q (0x8100), length 74: vlan 105, p 0, ethertype IPv4, 192.168.1.5 > 10.13.2.205: ICMP host 192.168.1.5 unreachable, length 36

12:00:44.131990 In f0:cb:a1:6f:eb:38 > ff:ff:ff:ff:ff:ff, ethertype 802.1Q (0x8100), length 64: vlan 105, p 0, ethertype ARP, arp who-has 10.13.0.1 tell 10.13.3.98

12:00:44.132119 Out 2c:21:72:9d:6a:01 > f0:cb:a1:6f:eb:38, ethertype 802.1Q (0x8100), length 46: vlan 105, p 0, ethertype ARP, arp reply 10.13.0.1 is-at 2c:21:72:9d:6a:01

12:00:44.151793 In f0:cb:a1:6f:eb:38 > ff:ff:ff:ff:ff:ff, ethertype 802.1Q (0x8100), length 64: vlan 105, p 0, ethertype ARP, arp who-has 169.254.255.255 tell 10.13.3.98

12:00:44.243950 In f0:cb:a1:6f:eb:38 > ff:ff:ff:ff:ff:ff, ethertype 802.1Q (0x8100), length 64: vlan 105, p 0, ethertype ARP, arp who-has 10.13.0.1 tell 10.13.3.98

12:00:44.244079 Out 2c:21:72:9d:6a:01 > f0:cb:a1:6f:eb:38, ethertype 802.1Q (0x8100), length 46: vlan 105, p 0, ethertype ARP, arp reply 10.13.0.1 is-at 2c:21:72:9d:6a:01

12:00:44.447345 In f0:cb:a1:6f:eb:38 > ff:ff:ff:ff:ff:ff, ethertype 802.1Q (0x8100), length 64: vlan 105, p 0, ethertype ARP, arp who-has 169.254.255.255 tell 10.13.3.98

12:00:44.701857 In 18:34:51:f0:6c:61 > ff:ff:ff:ff:ff:ff, ethertype 802.1Q (0x8100), length 64: vlan 105, p 0, ethertype ARP, arp who-has 10.13.0.1 tell 10.13.2.149

12:00:44.701974 Out 2c:21:72:9d:6a:01 > 18:34:51:f0:6c:61, ethertype 802.1Q (0x8100), length 46: vlan 105, p 0, ethertype ARP, arp reply 10.13.0.1 is-at 2c:21:72:9d:6a:01

12:00:44.722714 In 18:34:51:f0:6c:61 > ff:ff:ff:ff:ff:ff, ethertype 802.1Q (0x8100), length 64: vlan 105, p 0, ethertype ARP, arp who-has 169.254.255.255 tell 10.13.2.149

12:00:44.770992 In f0:cb:a1:6f:eb:38 > ff:ff:ff:ff:ff:ff, ethertype 802.1Q (0x8100), length 64: vlan 105, p 0, ethertype ARP, arp who-has 169.254.255.255 tell 10.13.3.98

12:00:44.866693 In 18:34:51:f0:6c:61 > ff:ff:ff:ff:ff:ff, ethertype 802.1Q (0x8100), length 64: vlan 105, p 0, ethertype ARP, arp who-has 10.13.0.1 tell 10.13.2.149

12:00:44.866825 Out 2c:21:72:9d:6a:01 > 18:34:51:f0:6c:61, ethertype 802.1Q (0x8100), length 46: vlan 105, p 0, ethertype ARP, arp reply 10.13.0.1 is-at 2c:21:72:9d:6a:01

12:00:45.060838 In 18:34:51:f0:6c:61 > ff:ff:ff:ff:ff:ff, ethertype 802.1Q (0x8100), length 64: vlan 105, p 0, ethertype ARP, arp who-has 169.254.255.255 tell 10.13.2.149

^C

23 packets received by filter

Bronze

Re: Problems with obtaining IP addresses

Hi Anna,

Your filter output has through so many variables in the mix. You have arp broadcasts going to different subnets

Please answer the following questions:

1. On the WLC, I presume that you have 2 interfaces, management and AP-manager. If so  what is the IP address/mask of the AP-mgr interface.

2. Did you set up a dynamic vlan for clients and if so what is the IP address/mask

3. What are the IP addresses/mask for Vlans 100 and 105.

4. Could paste a copy of the config for the Advanced tab for WLAN setting on the controller and also the interface setting for both the management interface and other interfaces configure on the controller. You can attach as a word document.

Like I said before, if your management interface, AP-manager interface and other dynamic interfaces are on different IP subnet, then the vlans must be routable through a router or L3 switch.

New Member

Re: Problems with obtaining IP addresses

Thank you for your help. I can’t express how much I appreciate the feedback. I will try to answer the questions as best I can.

Bronze

Re: Problems with obtaining IP addresses

Anna,

You could you also issue the follwing commands at the controller prompt and paste the results;

1. show interface summary

2. show wlan id (id = 1,2,3.........)

Bronze

Re: Problems with obtaining IP addresses

Anna,

From the document that you posted, it shows that the controller is not set up as the dhcp server. This is because the dhcp server override button is not ticked. If you want the wlc to be the dhcp server, you must tick the button. When you tick the button, another box will appear requesting that you specify the IP of the dhcp server. This should be the Wireless users interface which is 10.13.0.2.

The next step is to set up a dhcp pool. This is done by going to the Controller menu and clicking on the Internal DHCP server sub-menu and complete the information such as DHCP pool (10.13.0.4 - 10.13.0.x), subnet - 10.13.0.14.0, and DNS server. I assume that you are using a 24 bit mask.

The next step is to enable routing between the management vlan (100) and the dynamic vlan (105). This will be done on the L3 switch. Hence you configure interface vlans and assign IP addresses such 10.1.1.202 (vlan 100) and 10.13.0.1 (vlan 105.)

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