DHCP relay query

[Translator]

Hi, I'd like to make an inquiry. When a computer performs a DHCP broadcast request, I imagine that it reaches servers both within its network and beyond (if DHCP relay is configured on the router). If this is an external server where you have configured multiple scopes with different networks, how does the scope server know which to provide the data, and does it look at the gateway from which the request is received? Thank you very much.  

[Joseph W. Doherty]

The relayed DHCP packet provides the necessary data.

[sdroy · Accepted solution]

When a computer sends a DHCP request across the network, and it is relayed to an external DHCP server, the relay agent (like a router) includes its own IP address in a field called the Gateway IP Address (GIADDR) in the DHCP message. The DHCP server uses this GIADDR field to identify the subnet from which the request originated, then matches it to a specific scope—a configuration on the server defining the IP range and network settings for that subnet. Based on this match, the server assigns an IP address from the appropriate scope to the client, ensuring that it belongs to the correct network.

[Translator]

Check how DHCP works :#

https://www.cisco.com/en/US/docs/switches/lan/catalyst3850/software/release/3se/consolidated_guide/b_consolidated_3850_3se_cg_chapter_0111011.pdf

[Translator]

Check how DHCP works :#

https://www.cisco.com/en/US/docs/switches/lan/catalyst3850/software/release/3se/consolidated_guide/b_consolidated_3850_3se_cg_chapter_0111011.pdf