Dell PowerConnect M6348 Configuration Manual

Also see for PowerEdge M520: Manual Command reference guide Owner's manual Information update Release notes

Contents

Dell PowerConnect M6348 Configuration Manual Manual pdf 93 page image

Routing Configuration 93Certain pre-existing configurable DHCP relay options do not apply to relay of other protocols. Theseoptions are unchanged. The user may optionally set a maximum hop count or minimum wait time usingthe bootpdhcprelay maxhopcount and bootpdhcprelay minwaittime commands.The relay agent relays DHCP packets in both directions. It relays broadcast packets from the client toone or more DHCP servers, and relays packets to the client that the DHCP server unicasts back to therelay agent. For other protocols, the relay agent only relays broadcast packets from the client to the server.Packets from the server back to the client are assumed to be unicast directly to the client. Because thereis no relay in the return direction for protocols other than DHCP, the relay agent retains the source IPaddress from the original client packet. The relay agent uses a local IP address as the source IP address ofrelayed DHCP client packets.When a switch receives a broadcast UDP packet on a routing interface, the relay agent verifies that theinterface is configured to relay to the destination UDP port. If so, the relay agent unicasts the packet tothe configured server IP addresses. Otherwise, the relay agent verifies that there is a global configurationfor the destination UDP port. If so, the relay agent unicasts the packet to the configured server IPaddresses. Otherwise the packet is not relayed.NOTE: If the packet matches a discard relay entry on the ingress interface, the packet is not forwarded,regardless of the global configuration.The relay agent only relays packets that meet the following conditions:• The destination MAC address must be the all-ones broadcast address (FF:FF:FF:FF:FF:FF).• The destination IP address must be the limited broadcast address (255.255.255.255) or a directedbroadcast address for the receive interface.• The IP time-to-live (TTL) must be greater than 1.• The protocol field in the IP header must be UDP (17).• The destination UDP port must match a configured relay entry.CLI ExamplesExample 1: Enable/Disable IP HelperTo globally enable/disable IP Helper (relay of UDP packets) use the following command:console (config)#ip helper enableconsole (config)#no ip helper enable