Chapter 8
| General Security Measures
DHCP Snooping
– 244 –
◆
Additional considerations when the switch itself is a DHCP client
– The port(s)
through which the switch submits a client request to the DHCP server must be
configured as trusted (using the
ip dhcp snooping trust
command). Note that
the switch will not add a dynamic entry for itself to the binding table when it
receives an ACK message from a DHCP server. Also, when the switch sends out
DHCP client packets for itself, no filtering takes place. However, when the
switch receives any messages from a DHCP server, any packets received from
untrusted ports are dropped.
Example
This example enables DHCP snooping globally for the switch.
Console(config)#ip dhcp snooping
Console(config)#
Related Commands
ip dhcp snooping vlan (246)
ip dhcp snooping trust (247)
ip dhcp snooping
information option
This command enables the DHCP Option 82 information relay for the switch. Use
the
no
form to disable this function.
Syntax
[
no
]
ip dhcp snooping information option
Default Setting
Disabled
Command Mode
Global Configuration
Command Usage
◆
DHCP provides a relay mechanism for sending information about the switch
and its DHCP clients to the DHCP server. 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.
◆
When the DHCP Snooping Information Option 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 by the switch port to
which they are connected rather than just their MAC address. DHCP client-
server exchange messages are then forwarded directly between the server and
client without having to flood them to the entire VLAN.
◆
DHCP snooping must be enabled on the switch for the DHCP Option 82
information to be inserted into packets.
Summary of Contents for EX-3524
Page 2: ......
Page 28: ...Figures 28 ...
Page 34: ...Section I Getting Started 34 ...
Page 58: ...Chapter 1 Initial Switch Configuration Setting the System Clock 58 ...
Page 72: ...Chapter 2 Using the Command Line Interface CLI Command Groups 72 ...
Page 156: ...Chapter 5 SNMP Commands Notification Log Commands 156 ...
Page 164: ...Chapter 6 Remote Monitoring Commands 164 ...
Page 218: ...Chapter 7 Authentication Commands Management IP Filter 218 ...
Page 268: ...Chapter 8 General Security Measures Port based Traffic Segmentation 268 ...
Page 292: ...Chapter 9 Access Control Lists ACL Information 292 ...
Page 312: ...Chapter 10 Interface Commands Power Savings 312 ...
Page 324: ...Chapter 11 Link Aggregation Commands Trunk Status Display Commands 324 ...
Page 366: ...Chapter 15 Address Table Commands 366 ...
Page 428: ...Chapter 17 VLAN Commands Configuring Voice VLANs 428 ...
Page 572: ...Chapter 25 IP Interface Commands IPv6 Interface 572 ...
Page 578: ...Section I Appendices 578 ...