User Datagram Protocol

For introductory information about user datagram protocol (UDP), see UDP broadcast forwarding.

Configuring and enabling UDP broadcast forwarding

To configure and enable UDP broadcast forwarding on the switch:

Enable routing.
Globally enable UDP broadcast forwarding.
On a per-VLAN basis, configure a forwarding address and UDP port type for each type of incoming UDP broadcast you want routed to other VLANs.

Globally enabling UDP broadcast forwarding

Syntax:

[no] ip udp-bcast-forward

Enables or disables UDP broadcast forwarding on the routing switch. Routing must be enabled before executing this command.

Using the no form of this command disables any ip forward protocol udp commands configured in VLANs on the switch.

Default: Disabled

Configuring UDP broadcast forwarding on individual VLANs

This command routes an inbound UDP broadcast packet received from a client on the VLAN to the unicast or broadcast address configured for the UDP port type.

Syntax:

[no] ip forward-protocol udp ip-address [ port-number | port-name ]

Used in a VLAN context to configure or remove a server or broadcast address and its associated UDP port number. You can configure a maximum of 16 forward-protocol udp assignments in a given VLAN. The switch allows a total of 256 forward-protocol udp assignments across all VLANs.

You can configure UDP broadcast forwarding addresses regardless of whether UDP broadcast forwarding is globally enabled on the switch. However, the feature does not operate unless globally enabled.

ip-address

This can be either of the following:

The unicast address of a destination server on another subnet. For example: 15.75.10.43.
The broadcast address of the subnet on which a destination server operates. For example, the following address directs broadcasts to All hosts in the 15.75.11.0 subnet: 15.75.11.255.


	NOTE: The subnet mask for a forwarded UDP packet is the same as the subnet mask for the VLAN (or subnet on a multinetted VLAN) on which the UDP broadcast packet was received from a client.

udp-port-# Any UDP port number corresponding to a UDP application supported on a device at the specified unicast address or in the subnet at the specified broadcast address. For more information on UDP port numbers, refer to TCP/UDP port number ranges.

port-name

Allows use of common names for certain well-known UDP port numbers. You can type in the specific name instead of having to recall the corresponding number:

`dns`	Domain name service (53)
`ntp`	Network time protocol (123)
`netbios-ns`	NetBIOS name service (137)
`netbios-dgm`	NetBIOS datagram service (138)
`radius`	Remote authentication dial-in user service (1812)
`radius-old`	Remote authentication dial-in user service (1645)
`rip`	Routing information protocol (520)
`snmp`	Simple network management protocol (161)
`snmp-trap`	Simple network management protocol (162)
`tftp`	Trivial file transfer protocol (69)
`timep`	Time protocol (37)

Example

The following command configures the routing switch to forward UDP broadcasts from a client on VLAN 1 for a time protocol server:
HP Switch(vlan-1)# ip forward-protocol udp 15.75.11.155 timep

Viewing the current IP forward-protocol configuration

Syntax:

show ip forward-protocol [vlan vid]

Displays the current status of UDP broadcast forwarding and lists the UDP forwarding addresses configured on all static VLANS in the switch or on a specific VLAN.

Example:

Displaying global IP forward-protocol status and configuration

This example shows the global display showing UDP broadcast forwarding status and configured forwardig addresses for inbound UDP broadcast traffic for all VLANs configured on the routing switch.

HP Switch(config)# show ip forward-protocol

 IP Forwarder Addresses

    UDP Broadcast Forwarding: Disabled

 VLAN: 1
  IP Forward Addresses UDP Port
  -------------------- --------
  15.75.11.43          37
  15.75.11.255         53
  15.75.12.255         1813

 VLAN: 2
  IP Forward Addresses UDP Port
  -------------------- --------
  15.75.12.255         1812

Displaying IP forward-protocol status and per-VLAN configuration

This example shows the display of UDP broadcast forwarding status and the configured forwarding addresses for inbound UDP broadcast traffic on VLAN 1.

HP Switch(config)# show ip forward-protocol vlan 1

 IP Forwarder Addresses

    UDP Broadcast Forwarding: Disabled

 IP Forward Addresses UDP Port
 -------------------- --------
 15.75.11.43          37
 15.75.11.255         53
 15.75.12.255         1813

Operating notes for UDP broadcast forwarding

Maximum number of entries

The number of UDP broadcast entries and IP helper addresses combined can be up to 16 per VLAN, with an overall maximum of 2048 on the switch. (IP helper addresses are used with the switch's DHCP relay operation.)

For example, if VLAN 1 has 2 IP helper addresses configured, you can add up to 14 UDP forwarding entries in the same VLAN.

TCP/UDP port number ranges

There are three ranges:

Well-known ports: 0 to 1023
Registered ports: 1024 to 49151
Dynamic and/or private ports: 49152 to 65535

For more information, including a listing of UDP/TCP port numbers, go to the Internet Assigned Numbers Authority (IANA) website at:

www.iana.org

Then click on:

Protocol Number Assignment Services

P (Under "Directory of General Assigned Numbers" heading)

Port Numbers

Messages related to UDP broadcast forwarding

Message	Meaning
udp-bcast-forward: IP Routing support must be enabled first.	Appears in the CLI if an attempt to enable UDP broadcast forwarding has been made without IP routing being enabled first. Enable IP routing, then enable UDP broadcast forwarding.
UDP broadcast forwarder feature enabled	UDP broadcast forwarding has been globally enabled on the router. Appears in the Event Log and, if configured, in SNMP traps.
UDP broadcast forwarder feature disabled	UDP broadcast forwarding has been globally disabled on the routing switch. This action does not prevent you from configuring UDP broadcast forwarding addresses, but does prevent UDP broadcast forwarding operation. Appears in the Event Log and, if configured, in SNMP traps.
UDP broadcast forwarder must be disabled first.	Appears in the CLI if you attempt to disable routing while UDP forwarding is enabled on the switch.

prev		next
DHCP Option 82	home	UDP broadcast forwarding