Udp Broadcast Forwarding; Overview - HP 2920 Series Multicast And Routing Manual

If the Management VLAN IP address configuration changes after mgmt-vlan has been
configured as the remote ID suboption, the routing switch dynamically adjusts to the new IP
addressing for all future DHCP requests.
The Management VLAN and all other VLANs on the routing switch use the same MAC address.

UDP broadcast forwarding

Overview

Some applications rely on client requests sent as limited IP broadcasts addressed to a UDP
application port. If a server for the application receives such a broadcast, the server can reply to
the client. Since typical router behavior, by default, does not allow broadcast forwarding, a client's
UDP broadcast requests cannot reach a target server on a different subnet unless the router is
configured to forward client UDP broadcasts to that server.
A switch with routing enabled includes optional per-VLAN UDP broadcast forwarding that allows
up to 256 server and/or subnet entries on the switch (16 entries per-VLAN.) If an entry for a
particular UDP port number is configured on a VLAN, and an inbound UDP broadcast packet with
that port number is received on the VLAN, the switch routes the packet to the appropriate subnet.
(Each entry can designate either a single device or a single subnet. The switch ignores any entry
that designates multiple subnets.)
NOTE: The number of UDP broadcast forwarding entries supported is affected by the number of
IP helper addresses configured to support DHCP relay. See
forwarding" (page
A UDP forwarding entry includes the desired UDP port number and can be either an IP unicast
address or an IP subnet broadcast address for the subnet the server is in. Thus, an incoming UDP
packet carrying the configured port number will be:
Forwarded to a specific host if a unicast server address is configured for that port number.
Broadcast on the appropriate destination subnet if a subnet address is configured for that port
number.
A UDP forwarding entry for a particular UDP port number is always configured in a specific VLAN
and applies only to client UDP broadcast requests received inbound on that VLAN. If the VLAN
includes multiple subnets, the entry applies to client broadcasts with that port number from any
subnet in the VLAN.
For example, VLAN 1 (15.75.10.1) is configured to forward inbound UDP packets as shown in
Table 9.
Table 9 Example of a UDP packet-forwarding environment
Interface IP address
VLAN 1 15.75.10.1
VLAN 2 15.75.1 1.1
76 IP Routing Features
79).
Subnet mask Forwarding
address
255.255.255.0 15.75.1 1.43
15.75.1 1.255
15.75.12.255
255.255.255.0 None
"Operating notes for UDP broadcast
UDP Notes
port
1 188 Unicast address for forwarding inbound UDP
packets with UDP port 1 188 to a specific device
on VLAN 2.
1812 Broadcast address for forwarding inbound UDP
packets with UDP port 1812 to any device in the
15.75.1 1.0 network.
1813 Broadcast address for forwarding inbound UDP
packets with UDP port 1813 to any device in the
15.75.12.0 network.
N/A Destination VLAN for UDP 1 188 broadcasts from
clients on VLAN 1. The device identified in the