DHCP Snooping on a multi-switch topology
DHCP snooping is not a feature that requires communication between switches in order to be enabled across multiple devices. There is no negotiation between switches involved to make it work. DHCP snooping operates on a per-interface basis, where ports aredefined as either trusted or untrusted.
Now if you have multiple switches, then it is necessary to make all of the DHCP-server-facing interfaces trusted. In other words, based on your topology, any port that can expect to see legitimate incoming DHCP OFFER packets from the DHCP server should be trusted.
Unless you have some specialized requirements, the basic rule of thumb is to make ports connected to other switches trusted ports, and ports that connect to hosts untrusted ports.
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