Dell PowerConnect 7048P User Manual - Page 910

Table 33-1. Default Ports - UDP Port Numbers Implied By Wildcard Protocol IEN-116 Name Service DNS NetBIOS Name Server NetBIOS Datagram Server TACACS Server Time Service DHCP Trivial File Transfer Protocol UDP Port Number 42 53 137 138 49 37 67 69 The system limits the number of relay entries to four times the maximum number of routing interfaces (512 relay entries). There is no limit to the number of relay entries on an individual interface, and no limit to the number of servers for a given {interface, UDP port} pair. Certain configurable DHCP relay options do not apply to relay of other protocols. You may optionally set a maximum hop count or minimum wait time using the bootpdhcprelay maxhopcount and bootpdhcprelay minwaittime commands. The relay agent relays DHCP packets in both directions. It relays broadcast packets from the client to one or more DHCP servers, and relays packets to the client that the DHCP server unicasts back to the relay agent. For other protocols, the relay agent only relays broadcast packets from the client to the server. Packets from the server back to the client are assumed to be unicast directly to the client. Because there is no relay in the return direction for protocols other than DHCP, the relay agent retains the source IP address from the original client packet. The relay agent uses a local IP address as the source IP address of relayed DHCP client packets. 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 910 Configuring L2 and L3 Relay Features