IP Helper/DHCP Relay Commands
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47
IP Helper/DHCP Relay Commands
The IP Helper feature provides the ability for a router to forward configured
UDP broadcast packets to a particular IP address. 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 (with the limited
broadcast address 255.255.255.255, or a network directed broadcast address).
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 relays 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 47-1
.
Table 47-1. UDP Destination Ports
Protocol
UDP Port Number
IEN-116 Name Service
42
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Страница 76: ...Contents 76 ...
Страница 168: ...Command Groups 168 ...
Страница 242: ...Using the CLI 242 ...
Страница 244: ...244 Layer 2 Switching Commands ...
Страница 278: ...278 AAA Commands ...
Страница 287: ...Administrative Profiles Commands 287 global config ethernet config port channel config ...
Страница 288: ...288 Administrative Profiles Commands ...
Страница 326: ...326 Address Table Commands Maximum addresses 100 Learned addresses ...
Страница 332: ...332 Auto VoIP Commands ...
Страница 366: ...366 DHCP Management Interface Commands ...
Страница 464: ...464 Ethernet CFM Commands ...
Страница 478: ...478 Green Ethernet Commands ...
Страница 502: ...502 IGMP Snooping Commands ...
Страница 542: ...542 IPv6 Access List Commands ...
Страница 554: ...554 IPv6 MLD Snooping Commands ...
Страница 568: ...568 IP Source Guard Commands ...
Страница 580: ...580 iSCSI Optimization Commands ...
Страница 588: ...588 Link Dependency Commands ...
Страница 616: ...616 LLDP Commands ...
Страница 652: ...652 Port Channel Commands ...
Страница 656: ...656 Port Monitor Commands Session ID Admin Mode Probe Port Mirrored Port Type 1 Enable 1 0 10 1 0 8 Rx Tx ...
Страница 752: ...752 RADIUS Commands ...
Страница 784: ...784 Spanning Tree Commands ...
Страница 850: ...850 VLAN Commands ...
Страница 856: ...856 Voice VLAN Commands ...
Страница 888: ...888 802 1x Commands console show dot1x advanced gigabitethernet 1 0 2 Port Guest Unauthenticated VLAN Vlan 1 0 2 10 20 ...
Страница 890: ...890 Layer 3 Commands ...
Страница 934: ...934 DHCP Server and Relay Agent Commands ...
Страница 952: ...952 DHCPv6 Commands DHCPv6 Relay forward Packets Transmitted 0 Total DHCPv6 Packets Transmitted 0 ...
Страница 960: ...960 DVMRP Commands ...
Страница 980: ...980 IGMP Commands ...
Страница 988: ...988 IGMP Proxy Commands ...
Страница 1036: ...1036 IP Routing Commands ...
Страница 1109: ...IPv6 Routing Commands 1109 Tracing route over a maximum of 20 hops 1 N N N ...
Страница 1110: ...1110 IPv6 Routing Commands ...
Страница 1114: ...1114 Loopback Interface Commands ...
Страница 1144: ...1144 Multicast Commands ...
Страница 1296: ...1296 OSPFv3 Commands ...
Страница 1306: ...1306 Router Discovery Protocol Commands ...
Страница 1322: ...1322 Routing Information Protocol Commands console config router split horizon none ...
Страница 1328: ...1328 Tunnel Interface Commands ...
Страница 1354: ...1354 Utility Commands ...
Страница 1364: ...1364 Auto Install Commands ...
Страница 1406: ...1406 CLI Macro Commands ...
Страница 1424: ...1424 Clock Commands ...
Страница 1430: ...1430 Command Line Configuration Scripting Commands ...
Страница 1451: ...Configuration and Image File Commands 1451 console ...
Страница 1452: ...1452 Configuration and Image File Commands ...
Страница 1482: ...1482 Mode Commands ...
Страница 1517: ...Power Over Ethernet Commands 1517 Command Mode Privileged EXEC User Guidelines This command has no user guidelines ...
Страница 1518: ...1518 Power Over Ethernet Commands ...
Страница 1576: ...1576 Sflow Commands ...
Страница 1604: ...1604 SNMP Commands ...
Страница 1618: ...1618 SSH Commands ...
Страница 1640: ...1640 Syslog Commands ...
Страница 1708: ...1708 System Management Commands 5 ...
Страница 1716: ...1716 Terminal Length Commands ...
Страница 1734: ...1734 User Interface Commands Example The following example closes an active terminal session console quit ...
Страница 1786: ...1786 Appendix A List of Commands ...
Страница 1787: ...www dell com support dell com Printed in the U S A ...
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