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Cisco Systems, Inc.
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Configuring DHCP
Information About Configuring DHCP
This chapter describes how to configure Dynamic Host Configuration Protocol (DHCP) snooping and option-82 data
insertion, and the DHCP server port-based address allocation features on the switch. It also describes how to configure
the IP source guard feature.
DHCP Snooping
DHCP is widely used in LAN environments to dynamically assign host IP addresses from a centralized server, which
significantly reduces the overhead of administration of IP addresses. DHCP also helps conserve the limited IP address
space because IP addresses no longer need to be permanently assigned to hosts; only those hosts that are connected
to the network consume IP addresses.
DHCP Server
The DHCP server assigns IP addresses from specified address pools on a switch or router to DHCP clients and manages
them. If the DHCP server cannot give the DHCP client the requested configuration parameters from its database, it
forwards the request to one or more secondary DHCP servers defined by the network administrator.
DHCP Relay Agent
A DHCP relay agent is a Layer 3 device that forwards DHCP packets between clients and servers. Relay agents forward
requests and replies between clients and servers when they are not on the same physical subnet. Relay agent forwarding
is different from the normal Layer 2 forwarding, in which IP datagrams are switched transparently between networks.
Relay agents receive DHCP messages and generate new DHCP messages to send on output interfaces.
DHCP Snooping
DHCP snooping is a DHCP security feature that provides network security by filtering untrusted DHCP messages and by
building and maintaining a DHCP snooping binding database, also referred to as a DHCP snooping binding table.
DHCP snooping acts like a firewall between untrusted hosts and DHCP servers. You use DHCP snooping to differentiate
between untrusted interfaces connected to the end user and trusted interfaces connected to the DHCP server or another
switch.
Note:
For DHCP snooping to function properly, all DHCP servers must be connected to the switch through trusted
interfaces.
An untrusted DHCP message is a message that is received from outside the network or firewall. When you use DHCP
snooping in a service-provider environment, an untrusted message is sent from a device that is not in the
service-provider network, such as a customer’s switch. Messages from unknown devices are untrusted because they
can be sources of traffic attacks.
Содержание IE 4000
Страница 12: ...8 Configuration Overview Default Settings After Initial Switch Configuration ...
Страница 52: ...48 Configuring Interfaces Monitoring and Maintaining the Interfaces ...
Страница 108: ...104 Configuring Switch Clusters Additional References ...
Страница 128: ...124 Performing Switch Administration Additional References ...
Страница 130: ...126 Configuring PTP ...
Страница 140: ...136 Configuring CIP Additional References ...
Страница 146: ...142 Configuring SDM Templates Configuration Examples for Configuring SDM Templates ...
Страница 192: ...188 Configuring Switch Based Authentication Additional References ...
Страница 244: ...240 Configuring IEEE 802 1x Port Based Authentication Additional References ...
Страница 274: ...270 Configuring SGT Exchange Protocol over TCP SXP and Layer 3 Transport Configuring Cisco TrustSec Caching ...
Страница 298: ...294 Configuring VLANs Additional References ...
Страница 336: ...332 Configuring STP Additional References ...
Страница 408: ...404 Configuring DHCP Additional References ...
Страница 450: ...446 Configuring IGMP Snooping and MVR Additional References ...
Страница 490: ...486 Configuring SPAN and RSPAN Additional References ...
Страница 502: ...498 Configuring Layer 2 NAT ...
Страница 559: ...555 Configuring Network Security with ACLs How to Configure Network Security with ACLs Creating a Numbered Extended ACL ...
Страница 770: ...766 Configuring IPv6 MLD Snooping Related Documents ...
Страница 930: ...926 Configuring IP Unicast Routing Related Documents ...
Страница 956: ...952 Configuring IPv6 Unicast Routing Configuring IPv6 network 2010 AB8 2 48 network 2010 AB8 3 48 exit address family ...
Страница 976: ...972 Configuring Cisco IOS IP SLAs Operations Additional References ...
Страница 978: ...974 Dying Gasp ...
Страница 990: ...986 Configuring Enhanced Object Tracking Monitoring Enhanced Object Tracking ...
Страница 994: ...990 Configuring MODBUS TCP Displaying MODBUS TCP Information ...
Страница 996: ...992 Ethernet CFM ...
Страница 1030: ...1026 Working with the Cisco IOS File System Configuration Files and Software Images Working with Software Images ...
Страница 1066: ...1062 Using an SD Card SD Card Alarms ...