4000 Router Series Layer 3 - IP Services Configuration Guide

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Step Command Remarks

4. Specify the port as a trusted

port.

dhcp snooping trust

By default, all ports are untrusted

ports after DHCP snooping is

enabled.

5. Return to system view.

quit N/A

6. Enter interface view.

interface interface-type

interface-number

This interface must connect to the

DHCP client.

7. (Optional.) Enable recording

of DHCP snooping entries.

dhcp snooping binding record

By default, after DHCP snooping is

enabled, recording of DHCP

snooping entries is disabled.

Configuring Option 82

Follow these guidelines when you configure Option 82:

• To support Option 82, you must configure Option 82 on both the DHCP server and the DHCP

snooping device. For information about configuring Option 82 on the DHCP server, see "Enabling

handling o

f Option 82."

• If the handling strategy is configured as replace, you must configure a padding format for Option

82. If the handling strategy is keep or drop, there is no need to configure any padding format.

• If Option 82 contains the device name, the device name must contain no spaces. Otherwise, DHCP

snooping drops the message. You can use the sysname command to specify the device name. For

more information about this command, see Fundamentals Command Reference.

• If DHCP snooping and QinQ work together or DHCP snooping receives a DHCP packet with two

VLAN tags, and the verbose padding format is adopted for Option 82, DHCP snooping fills the

VLAN ID field of sub-option 1 with outer VLAN tag.inner VLAN tag. For example, if the outer VLAN

tag is 10 (a in hexadecimal) and the inner VLAN tag is 20 (14 in hexadecimal), the VLAN ID is

000a.0014.

To configure DHCP snooping to support Option 82:

Ste

Command

Remarks

1. Enter system view.

system-view N/A

2. Enter interface view.

interface interface-type interface-number N/A

3. Enable DHCP snooping to

support Option 82.

dhcp snooping information enable

By default, DHCP snooping

does not support Option

82.

4. (Optional.) Configure a

handling strategy for DHCP

requests that contain Option

82.

dhcp snooping information strategy { drop

| keep | replace }

By default, the handling

strategy is replace.

5. (Optional.) Configure the

padding content and code

type for the circuit ID

sub-option.

dhcp snooping information circuit-id

{ [ vlan vlan-id ] string circuit-id | { normal |

verbose [ node-identifier { mac | sysname

| user-defined node-identifier } ] } [ format

{ ascii | hex } ] }

By default, the padding

format is normal and the

code type is hex for the

circuit ID sub-option.