Administrator Guide

Layer-2 and Layer-3 Relay Features 1161
When a switch receives a broadcast UDP packet on a routing interface, the
relay agent verifies that the interface is configured to relay to the destination
UDP port. If so, the relay agent unicasts the packet to the configured server IP
addresses. Otherwise, the relay agent verifies that there is a global
configuration for the destination UDP port. If so, the relay agent unicasts the
packet to the configured server IP addresses. Otherwise the packet is not
relayed.
The relay agent relays packets that meet only the following conditions:
• The destination MAC address must be the all-ones broadcast address
(FF:FF:FF:FF:FF:FF).
• The destination IP address must be the limited broadcast address
(255.255.255.255) or a directed broadcast address for the receive interface.
• The IP time-to-live (TTL) must be greater than 1.
• The protocol field in the IP header must be UDP (17).
• The destination UDP port must match a configured relay entry.
NOTE: If the packet matches a discard relay entry on the ingress interface, the
packet is not forwarded, regardless of the global configuration.