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Participant

Connection to DHCP Server Failed for 1 SSID Only

Hi Guys,

I have Cisco WLC 5520 in my deployment using 8.5.151.0 image. I have several active SSIDs on the WLC, all pointing to the same DHCP server. Recently, during operational one of the SSID suddenly lost the connection to DHCP server. Not only new clients that were not able to connect to the SSID, clients that connected will lose the connection once he turned off than turned on the WiFi again.  Other SSIDs were working normally.

Below are the lists of action that I tried:

-Restart DHCP server

-Change interface assignment on WLAN profile

-Delete and add again the interface on the controller

 

Since my deployment on SSO, I tried to issued "redundancy force-switchover" command twice so both WLC were restarted. At first, it was working fine for few days but then the problem comes again. I checked the log and SNMP trap, so far I got none. Any idea where I should look? Thanks

1 ACCEPTED SOLUTION

Accepted Solutions
Highlighted
Participant

Re: Connection to DHCP Server Failed for 1 SSID Only

After some googling, I think I might know the cause of the problem. It's the DHCP proxy mode. The setting is enabled. There are some bugs and workaround provided.

https://bst.cloudapps.cisco.com/bugsearch/bug/CSCvj93657/?rfs=iqvred

https://www.theroutingtable.com/cisco-wlc-dhcp-proxy-mode/

Let's see if this bug is the root cause.

View solution in original post

7 REPLIES 7
Highlighted
Beginner

Re: Connection to DHCP Server Failed for 1 SSID Only

Have you managed to do a packet capture in some points (let's say OTA capture and switchport facing controller) to look for any DHCP petition from those clients connected to the SSID?

Highlighted
Participant

Re: Connection to DHCP Server Failed for 1 SSID Only

No I have not. Since the port that connects WLC to the core is on trunk mode, hence there will be a lot of packets from other VLANs.

I suspected the problem is on WLC because when the problem happened, I connected my laptop to the same VLAN on the core using access port, the LAN was working normally.

Highlighted
Beginner

Re: Connection to DHCP Server Failed for 1 SSID Only

What about an OTA capture to see if the clients are sending DHCP requests? Or invoke WLC "debug dhcp packets enable" to look for those packets in the controller? Is it a Flexconnect deployment with local forwarding?

 

Highlighted
Participant

Re: Connection to DHCP Server Failed for 1 SSID Only

The OTA packet capture, does it require some soft of special software like Eye PA?

I will try to issue "debug dhcp packets enable" once the problem occurs again. What is the command to stop the debugging process?

Regarding the deployment, it's local mode.

Highlighted
Beginner

Re: Connection to DHCP Server Failed for 1 SSID Only

For the OTA packet capture you can use either MacBook native packet capture (https://support.metageek.com/hc/en-us/articles/200907740-Wireless-Packet-Capture-with-macOS) or Linux with compatible adapter (i.e. RTL881x) and tweaked drivers (i.e from aircrack-ng).

 

Additionally, the command to stop debuggin is "debug dhcp packet disable"

 

HTH
-Jesus

*** Rate All Helpful Responses ***

Highlighted
Participant

Re: Connection to DHCP Server Failed for 1 SSID Only

Hi,

Just happened again and the following messages appeared on debug message.

*DHCP Socket Task: Mar 03 17:35:52.083: [SA] 64:1c:b0:ef:ac:67 DHCP ciaddr: 0.0.0.0, yiaddr: 0.0.0.0
*DHCP Socket Task: Mar 03 17:35:52.083: [SA] 64:1c:b0:ef:ac:67 DHCP siaddr: 0.0.0.0, giaddr: 192.168.4.4
*DHCP Socket Task: Mar 03 17:35:52.083: [SA] 64:1c:b0:ef:ac:67 DHCP selecting relay 2 - control block settings:
dhcpServer: 0.0.0.0, dhcpNetmask: 0.0.0.0,
dhcpGateway: 0.0.0.0, dhcpRelay: 192.168.4.4 VLAN: 4
*DHCP Socket Task: Mar 03 17:35:52.162: [SA] a4:d9:90:3a:23:3f DHCP received op BOOTREQUEST (1) (len 306,vlan 85, port 8, encap 0xec03, xid 0x5b8e7ae2)
*DHCP Socket Task: Mar 03 17:35:52.162: [SA] a4:d9:90:3a:23:3f DHCP (encap type 0xec03) mstype 0ff:ff:ff:ff:ff:ff
*DHCP Socket Task: Mar 03 17:35:52.162: [SA] a4:d9:90:3a:23:3f DHCP selecting relay 1 - control block settings:
dhcpServer: 0.0.0.0, dhcpNetmask: 0.0.0.0,
dhcpGateway: 0.0.0.0, dhcpRelay: 192.168.4.4 VLAN: 4
*DHCP Socket Task: Mar 03 17:35:52.162: [SA] a4:d9:90:3a:23:3f DHCP selected relay 1 - 10.152.16.10 (local address 192.168.4.4, gateway 10.152.112.1, VLAN 4, port 8)
*DHCP Socket Task: Mar 03 17:35:52.162: [SA] a4:d9:90:3a:23:3f DHCP selecting relay 2 - control block settings:
dhcpServer: 0.0.0.0, dhcpNetmask: 0.0.0.0,
dhcpGateway: 0.0.0.0, dhcpRelay: 192.168.4.4 VLAN: 4
*DHCP Socket Task: Mar 03 17:35:52.162: [SA] a4:d9:90:3a:23:3f DHCP selected relay 2 - NONE (server address 0.0.0.0,local address 192.168.4.4, gateway 10.152.112.1, VLAN 4, port 8)
*DHCP Socket Task: Mar 03 17:35:52.162: [SA] a4:d9:90:3a:23:3f DHCP selecting relay 1 - control block settings:
dhcpServer: 0.0.0.0, dhcpNetmask: 0.0.0.0,
dhcpGateway: 0.0.0.0, dhcpRelay: 192.168.4.4 VLAN: 4
*DHCP Socket Task: Mar 03 17:35:52.162: [SA] a4:d9:90:3a:23:3f DHCP transmitting DHCP DISCOVER (1)
*DHCP Socket Task: Mar 03 17:35:52.162: [SA] a4:d9:90:3a:23:3f DHCP op: BOOTREQUEST, htype: Ethernet, hlen: 6, hops: 1
*DHCP Socket Task: Mar 03 17:35:52.162: [SA] a4:d9:90:3a:23:3f DHCP xid: 0xe27a8e5b (3799682651), secs: 3584, flags: 0
*DHCP Socket Task: Mar 03 17:35:52.162: [SA] a4:d9:90:3a:23:3f DHCP chaddr: a4:d9:90:3a:23:3f
*DHCP Socket Task: Mar 03 17:35:52.162: [SA] a4:d9:90:3a:23:3f DHCP siaddr: 0.0.0.0, giaddr: 192.168.4.4
*DHCP Socket Task: Mar 03 17:35:52.162: [SA] a4:d9:90:3a:23:3f DHCP selecting relay 2 - control block settings:
dhcpServer: 0.0.0.0, dhcpNetmask: 0.0.0.0,
dhcpGateway: 0.0.0.0, dhcpRelay: 192.168.4.4 VLAN: 4
*DHCP Socket Task: Mar 03 17:35:52.172: [SA] f8:ff:c2:ed:60:28 DHCP received op BOOTREQUEST (1) (len 308,vlan 85, port 8, encap 0xec03, xid 0x5f83ac5d)
*DHCP Socket Task: Mar 03 17:35:52.172: [SA] f8:ff:c2:ed:60:28 DHCP (encap type 0xec03) mstype 0ff:ff:ff:ff:ff:ff
*DHCP Socket Task: Mar 03 17:35:52.172: [SA] f8:ff:c2:ed:60:28 DHCP selecting relay 1 - control block settings:
dhcpServer: 0.0.0.0, dhcpNetmask: 0.0.0.0,
dhcpGateway: 0.0.0.0, dhcpRelay: 192.168.4.4 VLAN: 4
*DHCP Socket Task: Mar 03 17:35:52.172: [SA] f8:ff:c2:ed:60:28 DHCP selected relay 1 - 10.152.16.10 (local address 192.168.4.4, gateway 10.152.112.1, VLAN 4, port 8)
*DHCP Socket Task: Mar 03 17:35:52.172: [SA] f8:ff:c2:ed:60:28 DHCP selecting relay 2 - control block settings:
dhcpServer: 0.0.0.0, dhcpNetmask: 0.0.0.0,
dhcpGateway: 0.0.0.0, dhcpRelay: 192.168.4.4 VLAN: 4

Somehow it happens on this VLAN only.

Highlighted
Participant

Re: Connection to DHCP Server Failed for 1 SSID Only

After some googling, I think I might know the cause of the problem. It's the DHCP proxy mode. The setting is enabled. There are some bugs and workaround provided.

https://bst.cloudapps.cisco.com/bugsearch/bug/CSCvj93657/?rfs=iqvred

https://www.theroutingtable.com/cisco-wlc-dhcp-proxy-mode/

Let's see if this bug is the root cause.

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