DELL N3000 User Manual

Configuring L2 and L3 Relay Features

The system limits the total number of relay entries to four times the 

maximum number of routing interfaces (512 relay entries). There is no 

individual limit to the number of relay entries on an individual interface, and 

no individual limit to the number of servers for a given {interface, UDP port} 

pair. The system limit applies in these cases.
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 

IEN-116 Name Service

42

DNS

53

NetBIOS Name Server

137

NetBIOS Datagram Server

138

TACACS Server

49

Time Service

37

DHCP

67 

Trivial File Transfer Protocol

69