HP 3400CL-24G manual UDP Broadcast Forwarding, Dhcp Operation for the Topology in Figure

Enhancements

Release M.08.94 Enhancements

Table 3. DHCP Operation for the Topology in Figure 12

Client	Remote ID	giaddr*	DHCP
			Server
X	10.38.10.1	10.39.10.1	A only If a DHCP client is in the Management VLAN, then its DHCP requests
				can go only to a DHCP server that is also in the Management VLAN.
				Routing to other VLANs is not allowed.
Y	10.38.10.1	10.29.10.1	B or C Clients outside of the Management VLAN can send DHCP requests
Z	10.38.10.1	10.15.10.1	B or C	only to DHCP servers outside of the Management VLAN. Routing to
				the Management VLAN is not allowed.

*The IP address of the primary DHCP relay agent receiving a client request packet is automatically added to the packet, and is identified as the giaddr (gateway interface address). This is the IP address of the VLAN on which the request packet was received from the client. For more information, refer to RFC 2131 and RFC 3046.

Operating Notes

■Routing is not allowed between the Management VLAN and other VLANs. Thus, a DHCP server must be available in the Management VLAN if there are clients in the Management VLAN that require a DHCP server.

■If the Management VLAN IP address configuration changes after mgmt-vlanhas been config- ured 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

Beginning with software release M.08.94, UDP Broadcast Forwarding is available on the ProCurve 3400cl and 6400cl switches. For further information, refer to the section titled “UDP Broadcast Forwarding on 5300xl Switches” in the “IP Routing Features” chapter of the Advanced Traffic Management Guide for your switch. (Note that this manual covers multiple switches and the description of UDP Broadcast Forwarding is no longer restricted to just the 5300xl switches.)

Some applications rely on client requests sent as limited IP broadcasts addressed to a UDP applica- tion 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, then 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.)

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