TL-SG108E V6: Wrong Source IP in DHCP DISCOVER messages

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TL-SG108E V6: Wrong Source IP in DHCP DISCOVER messages

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TL-SG108E V6: Wrong Source IP in DHCP DISCOVER messages
TL-SG108E V6: Wrong Source IP in DHCP DISCOVER messages
2022-11-08 17:01:20 - last edited 2022-11-09 12:55:52
Model: TL-SG108E  
Hardware Version: V6
Firmware Version: 1.0.0 Build 20220930 Rel.35985

When the switch is configured with DHCP enabled, it uses the wrong source IP in DHCP DISCOVER messages.

 

Per DHCP RFC, the source address should be 0.0.0.0, but it is in fact 192.168.0.1.

 

This causes issues with DHCP server running on linux with rp_filter active if using a different network than 192.168.0.0/24 as local address range.

If rp_filter is active (/proc/sys/net/ipv4/conf/all/rp_filter = 1 and/or /proc/sys/net/ipv4/conf/${interface}/rp_filter = 1), the packets will be dropped before reaching the DHCP server because the source IP (192.168.0.1) is invalid for this certain interface.

 

One fix is to disable rp_filter for the given interfaces (and also "all"), but a better option would be a firmware which sets the source IP to 0.0.0.0 for the DHCP DISCOVER packets...

 

Here is the sentence from the DHCP RFC 2131 Section 4.1 :

 

   DHCP messages broadcast by a client prior to that client obtaining
   its IP address must have the source address field in the IP header
   set to 0.

 

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Re:TL-SG108E V6: Wrong Source IP in DHCP DISCOVER messages
2022-11-10 08:30:52

  @georgmu 

 

By default, the switch will default to an IP address of 192.168.0.1 if it can't get an IP address from the front end properly.

The problem is most likely a problem with the DHCP Server in your network, and it would be more helpful if you could briefly describe the current network topology.

 

Also, can you confirm that the dhcp server in your network can assign IP addresses to other devices properly?

Just striving to develop myself while helping others.
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Re:TL-SG108E V6: Wrong Source IP in DHCP DISCOVER messages
2022-11-10 09:07:31 - last edited 2022-11-10 09:12:05

  @Virgo 

Thanks for your response, but no, the DHCP client of the switch does not follow the standard. See attached pictures showing the DHCP DISCOVER packet of the switch:

 

This is the wrong behavior:

 

 

And this is the correct behavior (like every other DHCP client does):

 

 

After a firmware update to the latest firmware, I saw this packet once, but after that, it falls back to the wrong behavior.

 

I can make it work with my DHCP server, but the behavior of the DHCP client is still wrong and I can only make it run by lowering the security level (by disabling rp_filter).

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Re:TL-SG108E V6: Wrong Source IP in DHCP DISCOVER messages
2022-11-14 08:34:59

Dear @georgmu,

 

Thank you so much for taking the time to post the issue on TP-Link community!

 

To better assist you, I've created a support ticket via your registered email address, and escalated it to our support engineer to look into the issue. 

The ticket ID is TKID221119283, please check your email box and ensure the support email is well received. Thanks!

Once the issue is addressed or resolved, welcome to update this topic thread with your solution to help others who may encounter the same issue as you did.

 

Many thanks for your great cooperation and patience!

Best Regards! >> Omada EAP Firmware Trial Available Here << >> Get the Latest Omada SDN Controller Releases Here << *Try filtering posts on each forum by Label of [Early Access]*
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