
User’s Guide
FUJITSU PSWITCH
December/2018
141
Protocol
UDP Port Number
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
Table 3-7: Default Ports
—
UDP Port Numbers Implied by Wildcard
The relay agent relays DHCP packets in both directions. It relays broadcast packets
from clients to one or more DHCP servers and relays the client packets that the
DHCP server sent back to the relay agent in unicast. For other protocols, the relay
agent relays only broadcast packets from the client to the server. Packets from the
server to the client are considered unicast to the client directly. Since there is no
relay in the return direction with protocols other than DHCP, the relay agent holds
the source IP address from the original client packet. The relay agent uses the local
IP address as the source IP address of the relayed DHCP client packet.
When the relay agent receives a broadcast UDP packet on the routing interface, it
checks whether the interface is configured to relay the destination UDP port. If
configured, the relay agent unicasts the packet to the configured server IP address.
If it is not configured, the relay agent checks whether there is a global
configuration of the destination UDP port. If there is a global configuration of the
destination UDP port, the relay agent unicasts the packet to the configured server
IP address. Otherwise, the packet is not relayed. Please note that packets will not
be transferred regardless of the global setting if the packet matches the discard
relay entry on the ingress interface.
The relay agent relays only packets that satisfy the following conditions:
The destination MAC address is all-ones broadcast address (FF: FF: FF: FF: FF: FF).
The destination IP address is a limited broadcast address (255.255.255.255) or a
direct broadcast address to the receiving interface.
IP time-to-live (TTL) is greater than 1.
The protocol field in the IP header is UDP (17).
The destination UDP port matches a configured relay entry.