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ip dhcp snooping trust

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DGS-1520 Series Gigabit Ethernet Smart Managed Switch CLI Reference Guide 23-8 ip dhcp snooping trust This command is used to configure a port as a trusted interface for DHCP snooping. Use the no form of this command to revert to the default setting. ip dhcp snooping trust no ip dhcp snooping trust Parameters None. Default By default, this option is disabled. Command Mode Interface Configuration Mode. Command Default Level Level: 12. Usage Guideline This command is available for physical port and port-channel interface configuration. Ports connected to the DHCP server or to other switches should be configured as trusted interfaces. The ports connected to DHCP clients should be configured as untrusted interfaces. DHCP snooping acts as a firewall between untrusted interfaces and DHCP servers. When a port is configured as a untrusted interface, the DHCP message arrives at the port on a VLAN that is enabled for DHCP snooping. The Switch forwards the DHCP packet unless any of the following conditions occur (in which case the packet is dropped): • The Switch port receives a packet (such as a DHCPOFFER, DHCPACK, DHCPNAK, or DHCPLEASEQUERY packet) from a DHCP server outside the firewall. • If the ip dhcp snooping verify mac-address command is enabled, the source MAC in the Ethernet header must be the same as the DHCP client hardware address to pass the validation. • The untrusted interface receives a DHCP packet that includes a relay agent IP address that is not 0.0.0.0 or the relay agent forward a packet that includes Option 82 to an untrusted interface. • The router receives a DHCPRELEASE or DHCPDECLINE message from an untrusted host with an entry in the DHCP snooping binding table, and the interface information in the binding table does not match the interface on which the message was received. In addition to doing the validation, DHCP snooping also create a binding entry based on the IP address assigned to client by the server in DHCP snooping binding database. The binding entry contains information including MAC address, IP address, the VLAN ID and port ID where the client is located, and the expiry of the lease time. Example This example shows how to enable DHCP snooping trust for port 3. Switch#configure terminal Switch(config)#interface eth1/0/3 Switch(config-if)#ip dhcp snooping trust Switch(config-if)# 265

Section	Page
Table of Contents	2
1. Introduction	5
Audience	5
Other Documentation	5
Conventions	5
Notes, Notices, and Cautions	5
Connecting to the Console Port	6
Command Descriptions	6
Command Modes	6
User EXEC Mode at Basic User Level	8
Privileged EXEC Mode at Operator Level	8
Privileged EXEC Mode at Administrator Level	8
Global Configuration Mode	8
Interface Configuration Mode	8
Creating a User Account	8
Interface Notation	9
Error Messages	10
Editing Features	11
Display Result Output Modifiers	11
2. Basic CLI Commands	13
2-1 help	13
Parameters	13
Default	13
Command Mode	13
Command Default Level	13
Usage Guideline	13
Example	13
2-2 enable	14
Parameters	14
Default	14
Command Mode	15
Command Default Level	15
Usage Guideline	15
Example	15
2-3 disable	15
Parameters	15
Default	15
Command Mode	15
Command Default Level	15
Usage Guideline	15
Example	16
2-4 configure terminal	16
Parameters	16
Default	16
Command Mode	16
Command Default Level	16
Usage Guideline	16
Example	16
2-5 login (EXEC)	16
Parameters	16
Default	17
Command Mode	17
Command Default Level	17
Usage Guideline	17
Example	17
2-6 login (Line)	17
Parameters	17
Default	17
Command Mode	17
Command Default Level	17
Usage Guideline	17
Example	18
2-7 logout	19
Parameters	19
Default	19
Command Mode	19
Command Default Level	19
Usage Guideline	19
Example	19
2-8 end	19
Parameters	19
Default	19
Command Mode	19
Command Default Level	20
Usage Guideline	20
Example	20
2-9 exit	20
Parameters	20
Default	20
Command Mode	20
Command Default Level	20
Usage Guideline	20
Example	20
2-10 show history	21
Parameters	21
Default	21
Command Mode	21
Command Default Level	21
Usage Guideline	21
Example	21
2-11 password-recovery	21
Parameters	21
Default	22
Command Mode	22
Command Default Level	22
Usage Guideline	22
Example	22
2-12 show environment	22
Parameters	22
Default	23
Command Mode	23
Command Default Level	23
Usage Guideline	23
Example	23
Display Parameters	23
2-13 show unit	24
Parameters	24
Default	24
Command Mode	24
Command Default Level	24
Usage Guideline	24
Example	24
2-14 show cpu utilization	24
Parameters	24
Default	25
Command Mode	25
Command Default Level	25
Usage Guideline	25
Example	25
2-15 show version	25
Parameters	26
Default	26
Command Mode	26
Command Default Level	26
Usage Guideline	26
Example	26
2-16 snmp-server enable traps environment	26
Parameters	26
Default	27
Command Mode	27
Command Default Level	27
Usage Guideline	27
Example	27
2-17 environment temperature threshold	27
Parameters	27
Default	27
Command Mode	27
Command Default Level	27
Usage Guideline	28
Example	28
2-18 show memory utilization	28
Parameters	28
Default	28
Command Mode	28
Command Default Level	28
Usage Guideline	28
Example	29
2-19 privilege	29
Parameters	29
Default	29
Command Mode	29
Command Default Level	29
Usage Guideline	29
Example	30
2-20 show privilege	30
Parameters	30
Default	30
Command Mode	30
Command Default Level	30
Usage Guideline	30
Example	30
3. 802.1X Commands	31
3-1 clear dot1x counters	31
Parameters	31
Default	31
Command Mode	31
Command Default Level	31
Usage Guideline	31
Example	31
3-2 dot1x control-direction	31
Parameters	31
Default	32
Command Mode	32
Command Default Level	32
Usage Guideline	32
Example	32
3-3 dot1x default	32
Parameters	32
Default	32
Command Mode	33
Command Default Level	33
Usage Guideline	33
Example	33
3-4 dot1x port-control	33
Parameters	33
Default	33
Command Mode	33
Command Default Level	33
Usage Guideline	33
Example	34
3-5 dot1x forward-pdu	34
Parameters	34
Default	34
Command Mode	34
Command Default Level	34
Usage Guideline	34
Example	34
3-6 dot1x initialize	34
Parameters	35
Default	35
Command Mode	35
Command Default Level	35
Usage Guideline	35
Example	35
3-7 dot1x max-req	35
Parameters	35
Default	35
Command Mode	36
Command Default Level	36
Usage Guideline	36
Example	36
3-8 dot1x pae authenticator	36
Parameters	36
Default	36
Command Mode	36
Command Default Level	36
Usage Guideline	36
Example	37
3-9 dot1x re-authenticate	37
Parameters	37
Default	37
Command Mode	37
Command Default Level	37
Usage Guideline	37
Example	38
3-10 dot1x system-auth-control	38
Parameters	38
Default	38
Command Mode	38
Command Default Level	38
Usage Guideline	38
Example	38
3-11 dot1x timeout	38
Parameters	39
Default	39
Command Mode	39
Command Default Level	39
Usage Guideline	39
Example	39
3-12 show dot1x	39
Parameters	39
Default	40
Command Mode	40
Command Default Level	40
Usage Guideline	40
Example	40
3-13 show dot1x diagnostics	40
Parameters	41
Default	41
Command Mode	41
Command Default Level	41
Usage Guideline	41
Example	41
3-14 show dot1x statistics	42
Parameters	42
Default	42
Command Mode	42
Command Default Level	42
Usage Guideline	42
Example	42
3-15 show dot1x session-statistics	43
Parameters	43
Default	43
Command Mode	43
Command Default Level	43
Usage Guideline	43
Example	43
3-16 snmp-server enable traps dot1x	43
Parameters	44
Default	44
Command Mode	44
Command Default Level	44
Usage Guideline	44
Example	44
4. Access Control List (ACL) Commands	45
4-1 access-list resequence	45
Parameters	45
Default	45
Command Mode	45
Command Default Level	45
Usage Guideline	45
Example	46
4-2 acl-hardware-counter	46
Parameters	46
Default	47
Command Mode	47
Command Default Level	47
Usage Guideline	47
Example	47
4-3 action	47
Parameters	47
Default	47
Command Mode	47
Command Default Level	47
Usage Guideline	48
Example	48
4-4 clear acl-hardware-counter	48
Parameters	48
Default	48
Command Mode	48
Command Default Level	48
Usage Guideline	49
Example	49
4-5 expert access-group	49
Parameters	49
Default	49
Command Mode	49
Command Default Level	49
Usage Guideline	49
Example	50
4-6 expert access-list	50
Parameters	50
Default	50
Command Mode	50
Command Default Level	50
Usage Guideline	50
Example	50
4-7 ip access-group	51
Parameters	51
Default	51
Command Mode	51
Command Default Level	51
Usage Guideline	51
Example	51
4-8 ip access-list	51
Parameters	52
Default	52
Command Mode	52
Command Default Level	52
Usage Guideline	52
Example	52
4-9 ipv6 access-group	52
Parameters	53
Default	53
Command Mode	53
Command Default Level	53
Usage Guideline	53
Example	53
4-10 ipv6 access-list	53
Parameters	53
Default	54
Command Mode	54
Command Default Level	54
Usage Guideline	54
Example	54
4-11 list-remark	54
Parameters	54
Default	54
Command Mode	55
Command Default Level	55
Usage Guideline	55
Example	55
4-12 mac access-group	55
Parameters	55
Default	55
Command Mode	55
Command Default Level	56
Usage Guideline	56
Example	56
4-13 mac access-list	56
Parameters	56
Default	56
Command Mode	56
Command Default Level	56
Usage Guideline	56
Example	57
4-14 match ip address	57
Parameters	57
Default	57
Command Mode	57
Command Default Level	57
Usage Guideline	57
Example	58
4-15 match ipv6 address	58
Parameters	58
Default	58
Command Mode	58
Command Default Level	58
Usage Guideline	58
Example	59
4-16 match mac address	59
Parameters	59
Default	59
Command Mode	59
Command Default Level	59
Usage Guideline	59
Example	60
4-17 permit \| deny \| deny-cpu (expert access-list)	60
Parameters	61
Default	62
Command Mode	62
Command Default Level	62
Usage Guideline	62
Example	63
4-18 permit \| deny \| deny-cpu (ip access-list)	63
Parameters	64
Default	65
Command Mode	65
Command Default Level	65
Usage Guideline	65
Example	66
4-19 permit \| deny \| deny-cpu (ipv6 access-list)	66
Parameters	67
Default	68
Command Mode	68
Command Default Level	68
Usage Guideline	68
Example	68
4-20 permit \| deny \| deny-cpu (mac access-list)	69
Parameters	69
Default	70
Command Mode	70
Command Default Level	70
Usage Guideline	70
Example	70
4-21 show access-group	70
Parameters	70
Default	71
Command Mode	71
Command Default Level	71
Usage Guideline	71
Example	71
4-22 show access-list	71
Parameters	71
Default	71
Command Mode	71
Command Default Level	72
Usage Guideline	72
Example	72
4-23 show vlan access-map	72
Parameters	73
Default	73
Command Mode	73
Command Default Level	73
Usage Guideline	73
Example	73
4-24 show vlan filter	74
Parameters	74
Default	74
Command Mode	74
Command Default Level	74
Usage Guideline	74
Example	74
4-25 vlan access-map	74
Parameters	75
Default	75
Command Mode	75
Command Default Level	75
Usage Guideline	75
Example	75
4-26 vlan filter	75
Parameters	75
Default	76
Command Mode	76
Command Default Level	76
Usage Guideline	76
Example	76
5. Access Management Commands	77
5-1 access class	77
Parameters	77
Default	77
Command Mode	77
Command Default Level	77
Usage Guideline	77
Example	77
5-2 banner login	77
Parameters	78
Default	78
Command Mode	78
Command Default Level	78
Usage Guideline	78
Example	78
5-3 do	78
Parameters	79
Default	79
Command Mode	79
Command Default Level	79
Usage Guideline	79
Example	79
5-4 prompt	79
Parameters	79
Default	80
Command Mode	80
Command Default Level	80
Usage Guideline	80
Example	80
5-5 enable password	80
Parameters	80
Default	81
Command Mode	81
Command Default Level	81
Usage Guideline	81
Example	81
5-6 ip http server	81
Parameters	81
Default	81
Command Mode	81
Command Default Level	81
Usage Guideline	81
Example	82

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DGS-1520 Series Gigabit Ethernet Smart Managed Switch CLI Reference Guide

265

23-8

ip dhcp snooping trust

This command is used to configure a port as a trusted interface for DHCP snooping. Use the

form of this

command to revert to the default setting.

ip dhcp snooping trust

no ip dhcp snooping trust

Parameters

None.

Default

By default, this option is disabled.

Command Mode

Interface Configuration Mode.

Command Default Level

Level: 12.

Usage Guideline

This command is available for physical port and port-channel interface configuration.

Ports connected to the DHCP server or to other switches should be configured as trusted interfaces. The ports

connected to DHCP clients should be configured as untrusted interfaces. DHCP snooping acts as a firewall

between untrusted interfaces and DHCP servers.

When a port is configured as a untrusted interface, the DHCP message arrives at the port on a VLAN that is

enabled for DHCP snooping. The Switch forwards the DHCP packet unless any of the following conditions occur

(in which case the packet is dropped):

•

The Switch port receives a packet (such as a DHCPOFFER, DHCPACK, DHCPNAK, or

DHCPLEASEQUERY packet) from a DHCP server outside the firewall.

•

If the

ip dhcp snooping verify mac-address

command is enabled, the source MAC in the Ethernet

header must be the same as the DHCP client hardware address to pass the validation.

•

The untrusted interface receives a DHCP packet that includes a relay agent IP address that is not 0.0.0.0

or the relay agent forward a packet that includes Option 82 to an untrusted interface.

•

The router receives a DHCPRELEASE or DHCPDECLINE message from an untrusted host with an entry

in the DHCP snooping binding table, and the interface information in the binding table does not match the

interface on which the message was received.

In addition to doing the validation, DHCP snooping also create a binding entry based on the IP address assigned to

client by the server in DHCP snooping binding database. The binding entry contains information including MAC

address, IP address, the VLAN ID and port ID where the client is located, and the expiry of the lease time.

Example

This example shows how to enable DHCP snooping trust for port 3.

Switch#configure terminal

Switch(config)#interface eth1/0/3

Switch(config-if)#ip dhcp snooping trust

Switch(config-if)#