Planet IGSW-2840, Руководство пользователя

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User’s Manual of IGSW-2840
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When the DHCP snooping is globally disabled, DHCP snooping can still be configured for specific VLANs, but the changes
will not take effect until DHCP snooping is globally re-enabled.
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When DHCP snooping is globally enabled, and DHCP snooping is then disabled on a VLAN, all dynamic bindings learned for
this VLAN are removed from the binding table.
Figure 4-11-51 DHCP Snooping VLAN Configuration screenshot
The page includes the following fields:
Object Description
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VLAN ID
ID of a configured VLAN. (Range: 1-4094)
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DHCP Snooping Status Enables or disables DHCP snooping for the selected VLAN.
4.11.16.3 Information Option Configuration
DHCP provides a relay mechanism for sending information about the switch and its DHCP clients to DHCP servers. Known as
DHCP Option 82, it allows compatible DHCP servers to use the information when assigning IP addresses, or to set other
services or policies for clients. It is also an effective tool in preventing malicious network attacks from attached clients on DHCP
services, such as IP Spoofing, Client Identifier Spoofing, MAC Address Spoofing, and Address Exhaustion.
Command Usage
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DHCP Snooping must be enabled for Option 82 to function.
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When Option 82 is enabled, the requesting client (or an intermediate relay agent that has used the information fields to
describe itself) can be identified in the DHCP request packets forwarded by the switch and in reply packets sent back from
the DHCP server.
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If Option 82 is enabled on the switch, client information may be included in any relayed request packet.
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DHCP request packets are flooded onto all attached VLANs other than the inbound VLAN under the following situations:
- DHCP snooping is disabled.
- The request packet contains a valid relay agent address field.
DHCP reply packets received by the relay agent (that is, this switch) are handled in the following way:
1. When the relay agent receives a DHCP reply packet with Option 82 information, it first ensures that the packet is
destined for it, and then removes the Option 82 field from the packet.