Dell PowerEdge M520 Dell PowerConnect M6220/M6348/M8024 Switches Configuration - Page 93

Example 1: Enable/Disable IP Helper

Get Dell PowerEdge M520 PDF manuals and user guides View all Dell PowerEdge M520 manuals
Add to My Manuals
Save this manual to your list of manuals

Page 93 highlights

Certain pre-existing configurable DHCP relay options do not apply to relay of other protocols. These options are unchanged. The user may optionally set a maximum hop count or minimum wait time using the bootpdhcprelay maxhopcount and bootpdhcprelay minwaittime commands. The relay agent relays DHCP packets in both directions. It relays broadcast packets from the client to one or more DHCP servers, and relays packets to the client that the DHCP server unicasts back to the relay 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 there is no relay in the return direction for protocols other than DHCP, the relay agent retains the source IP address from the original client packet. The relay agent uses a local IP address as the source IP address of relayed DHCP client packets. When a switch receives a broadcast UDP packet on a routing interface, the relay agent verifies that the interface is configured to relay to the destination UDP port. If so, the relay agent unicasts the packet to the configured server IP addresses. Otherwise, the relay agent verifies that there is a global configuration for the destination UDP port. If so, the relay agent unicasts the packet to the configured server IP addresses. 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 directed broadcast 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 Examples Example 1: Enable/Disable IP Helper To globally enable/disable IP Helper (relay of UDP packets) use the following command: console (config)#ip helper enable console (config)#no ip helper enable Routing Configuration 93

  • 1
  • 2
  • 3
  • 4
  • 5
  • 6
  • 7
  • 8
  • 9
  • 10
  • 11
  • 12
  • 13
  • 14
  • 15
  • 16
  • 17
  • 18
  • 19
  • 20
  • 21
  • 22
  • 23
  • 24
  • 25
  • 26
  • 27
  • 28
  • 29
  • 30
  • 31
  • 32
  • 33
  • 34
  • 35
  • 36
  • 37
  • 38
  • 39
  • 40
  • 41
  • 42
  • 43
  • 44
  • 45
  • 46
  • 47
  • 48
  • 49
  • 50
  • 51
  • 52
  • 53
  • 54
  • 55
  • 56
  • 57
  • 58
  • 59
  • 60
  • 61
  • 62
  • 63
  • 64
  • 65
  • 66
  • 67
  • 68
  • 69
  • 70
  • 71
  • 72
  • 73
  • 74
  • 75
  • 76
  • 77
  • 78
  • 79
  • 80
  • 81
  • 82
  • 83
  • 84
  • 85
  • 86
  • 87
  • 88
  • 89
  • 90
  • 91
  • 92
  • 93
  • 94
  • 95
  • 96
  • 97
  • 98
  • 99
  • 100
  • 101
  • 102
  • 103
  • 104
  • 105
  • 106
  • 107
  • 108
  • 109
  • 110
  • 111
  • 112
  • 113
  • 114
  • 115
  • 116
  • 117
  • 118
  • 119
  • 120
  • 121
  • 122
  • 123
  • 124
  • 125
  • 126
  • 127
  • 128
  • 129
  • 130
  • 131
  • 132
  • 133
  • 134
  • 135
  • 136
  • 137
  • 138
  • 139
  • 140
  • 141
  • 142
  • 143
  • 144
  • 145
  • 146
  • 147
  • 148
  • 149
  • 150
  • 151
  • 152
  • 153
  • 154
  • 155
  • 156
  • 157
  • 158
Routing Configuration
93
Certain pre-existing configurable DHCP relay options do not apply to relay of other protocols. These
options are unchanged. The user may optionally set a maximum hop count or minimum wait time using
the bootpdhcprelay maxhopcount and bootpdhcprelay minwaittime commands.
The relay agent relays DHCP packets in both directions. It relays broadcast packets from the client to
one or more DHCP servers, and relays packets to the client that the DHCP server unicasts back to the
relay 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 there
is no relay in the return direction for protocols other than DHCP, the relay agent retains the source IP
address from the original client packet. The relay agent uses a local IP address as the source IP address of
relayed DHCP client packets.
When a switch receives a broadcast UDP packet on a routing interface, the relay agent verifies that the
interface is configured to relay to the destination UDP port. If so, the relay agent unicasts the packet to
the configured server IP addresses. Otherwise, the relay agent verifies that there is a global configuration
for the destination UDP port. If so, the relay agent unicasts the packet to the configured server IP
addresses. 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 directed
broadcast 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 Examples
Example 1: Enable/Disable IP Helper
To globally enable/disable IP Helper (relay of UDP packets) use the following command:
console (config)#ip helper enable
console (config)#no ip helper enable