I have an SG500-52MP and I do not believe IPv4 DHCP pools created with a "Domain Name Server IP Address (Option 6)" are functioning as designed or expected. When a Windows 11 or Windows 10 PCs receives it's DHCP information, the IP identified in the SG500 "Domain Name Server IP Address (Option 6)" field of the pool is being populated in the "Connection-specific DNS Suffix" or "Primary DNS Suffix" of the Windows PCs and as a result the PC's DNS values are left blank. I suspect this is not Windows specific but related to the SG500 / 1.4.11.5 since I also had problems with IOT devices and some phones as well which were obtaining the DHCP properties from the SG500's DHCP pools - and they were not getting the correct DNS address. I instead managed to use my AP3802i's to create separate but equivalent DHCP pools and DNS addresses are being handled properly by the AP3802i's- but that only solves the issue on wireless IOT devices and Wi-Fi enabled phones/tablets. On all wired devices such as Linux or Windows PC, I have to manually predefine their correct DNS parameters on each PC and only populate the IPv4 IPs from from the SG500-52MP...
If I am populating the IP of my DNS server into the wrong part of the DHCP pool definition, please advise the correct methodology. FYI, I have tried using the drop-down to select my DNS server and I have tried applying my DNS as an Other option. Both ways fail for me...
Now I did some extra checking and I can get the DHCP service to work correctly if I use the CLI command to populate the dns-server IP. I did notice when I checked the GUI afterword, that it placed the dns-server IP in Domain Name (Option 15) field. That was unexpected (for me at least, but at least I now have a workaround instead of having to complicate my DHCP pool management over multiple servers... I just have to squint and little when I look at the GUI DHCP pool configurations... LOL
I was also able to add multiple DNS servers using the CLI interface. The GUI interface only shows the first DNS server in the Domain Name (Option 15) field. As a cautionary note. I did not test this but be careful if you edit the DNS pools using the GUI interface after making adding the correct configuration in the CLI. I'm not sure if any other GUI change on the DHCP pool will undo the correct change you made in the CLI interface...
It would be nice if Cisco could fix this in a subsequent firmware update but I know this is an older switch. If anyone else is having this same problem, I would suggest configuring your DHCP pools through the SSH / CLI interface...
