Ip Helper/Dhcp Relay Commands - Dell N1100-ON Reference Manual

IP Helper/DHCP Relay Commands

Dell EMC Networking N1500/N2000/N2100-ON/N3000/N3100-
ON/N4000 Series Switches
The IP Helper feature provides the ability for a router to forward configured
UDP broadcast packets to a particular IP address over a routed interface. This
allows applications to reach servers on non-local subnets. This is possible even
when the application is designed to assume a server is always on a local subnet
or when the application uses broadcast packets to reach the server (using the
broadcast MAC address FF:FF:FF:FF:FF:FF and with the IP broadcast
address 255.255.255.255 or a network directed broadcast IP address on the
receiving switch interface). IP routing must be enabled for IP Helper to
forward properly.
Network administrators can configure relay entries globally and on routing
interfaces. Each relay entry maps an ingress interface and destination UDP
port number to a single IPv4 address (the helper address). Multiple relay
entries may be configured for the same interface and UDP port, in which case
the relay agent unicasts matching packets to each server address. Interface
configuration takes priority over global configuration. If the destination UDP
port for a packet matches any entry on the ingress interface, the packet is
handled according to the interface configuration. If the packet does not
match any entry on the ingress interface, the packet is handled according to
the global IP helper configuration.
Network administrators can configure discard relay entries. Discard entries are
used to discard packets received on a specific interface when those packets
would otherwise be relayed according to a global relay entry. Discard relay
entries may be configured on interfaces, but are not configured globally.
Additionally, administrators can configure which UDP ports are forwarded.
Certain UDP port numbers can be specified by name in the UI, but network
administrators can configure a relay entry with any UDP port number.
Administrators may configure relay entries that do not specify a destination
UDP port. The relay agent assumes that these entries match packets with the
UDP destination ports listed in Table 7-1.
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Layer 3 Routing Commands