DHCP Loop

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NewToNetworking
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DHCP Loop

As my name indicates, I am pretty new to networking. I have an IP camera that suddenly lost its IP address and can only get one via DHCP. It went offline and started broadcasting Discover packets to get a new IP. From what I can see there are offers being sent to the camera but it is not requesting one of the two IPs that are being offered. Meraki is showing that on the port no offers are being received by the camera but when I do a packet capture on that specific port it shows that the offer is getting there. I did notice that on the offer packet it includes the IP address that is being offered as the destination and I do not think that is correct, but I could be wrong (ex. OFFER PACKET source: DHCP server IP / MAC , destination: DHCP offered IP / Camera MAC). DHCP relay is turned on and directed towards the DHCP Server. 

 

Note: Camera did work when plugged into another switch and gained a new IP dynamically for testing. 

Don't ask me why it is setup this way lol I am not the Architect or Engineer. 

 

Thank you for any help in advance. 

DHCP Issue.png

1 Accepted Solution
NewToNetworking
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I was trying to avoid rebooting anything but after rebooting the switch it was directly connected to it was able to grab the IP from the DHCP server. 

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7 Replies 7
Ryan_Miles
Meraki Employee
Meraki Employee

So, does VLAN 30 exist/is allowed on the trunks all the way to the L3 switch? Then on that L3 switch is there a DHCP helper/relay to the IP of the DHCP server?

 

And when you say the camera worked on another switch. Which one? The switchport is configured exactly the same, the uplink is configured the same?

Ryan / Meraki Solutions Engineer

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Yes VLAN 30 is allowed on all trunk ports that leads back to the DHCP server and relay is setup for the layer 3 router. Ports were configured the same way as well. Only difference is that the Native VLANs are different. One is on VLAN 1 and the one that it worked on was NATIVE VLAN 101. No configurations have been made when the camera went down and was working on this current setup for months before having an issue... I am thinking it has to do with the Offer packet sent by the DHCP server. It does not look like other packets that are issued. The destination is not 255.255.255.255 it includes the IP that is trying to be offered. 

RaphaelL
Kind of a big deal
Kind of a big deal

Hi ,

 

1- Is there a MX in the flow ? ( You posted this under Security & SD-WAN ) MXs had nasty DHCP bugs that were resolved under MX 15.44 and higher. DHCP renew might fail ( in our case 100% of the time )

 

2- DHCP process goes under D-O-R-A  ( Discover - Offer - Request - Ack ). However under the DHCP renew process , the packets are unicast ( since the client already has an valid IP )

 

3 - Do you have DHCP snooping enabled ?

 

4- Meraki is showing that on the port no offers are being received by the camera but when I do a packet capture on that specific port it shows that the offer is getting there.   Which device are you capturing the DHCP offers ?

There is a MX connected to the Layer 3 switch but I do not believe that the traffic flows through it. DHCP snooping is enabled. I see the offer packet and then it stops and loops back again. I am capturing the packets on the port of the switch that the camera is on. The offer packet is being sent as a unicast packet. Does it matter that the Discover packet has bootp flag is set to 0 for unicast? 

Are you capturing a renew or a new lease ? eg : if you reboot the device it may go through d-o-r-a. If the dhcp lease is around 75% expired the camera will do a dhcp renew ( r-a ) .Both the request and ack will be unicast.

 

Those are the common DHCP packets you will see on your network. 

RaphaelL_0-1660256850002.png

 

 

 

** I do not have a DHCP helper , the DHCP server is on the same LAN. Captures on your side will be slightly different.

No the only packets that are coming up under DHCP are Discover and Offer packets. DHCP Issue 2.png

NewToNetworking
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I was trying to avoid rebooting anything but after rebooting the switch it was directly connected to it was able to grab the IP from the DHCP server. 

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