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PowerConnect B-Series FCX Configuration Guide
53-1002266-01
DHCP snooping
39
How DHCP snooping works
When enabled on a VLAN, DHCP snooping stands between untrusted ports (those connected to
host ports) and trusted ports (those connected to DHCP servers). A VLAN with DHCP snooping
enabled forwards DHCP request packets from clients and discards DHCP server reply packets on
untrusted ports, and it forwards DHCP server reply packets on trusted ports to DHCP clients, as
shown in the following figures
FIGURE 176
DHCP snooping at work - on an untrusted port
FIGURE 177
DHCP snooping at work - on a trusted port
DHCP binding database
When it forwards DHCP server reply packets on trusted ports, the Dell PowerConnect device saves
the client IP-to-MAC address binding information in the DHCP binding database. This is how the
DHCP snooping binding table is populated. The information saved includes MAC address, IP
address, lease time, VLAN number, and port number.
In the Brocade device, the DHCP binding database is integrated with the enhanced ARP table,
which is used by Dynamic ARP Inspection. For more information, refer to
“ARP entries”
on
page 1346.
The lease time will be refreshed when the client renews its IP address with the DHCP server;
otherwise the Dell PowerConnect device removes the entry when the lease time expires.
Switch
DHCP server
reply packet
Trusted
Untrusted
DHCP
Server
DHCP
Snooping
DHCP client
request packet
DHCP
Client
Switch
DHCP server
reply packet
Trusted
Untrusted
DHCP
Server
DHCP
Snooping
Содержание PowerConnect B-FCXs
Страница 1: ...53 1002266 01 18 March 2011 PowerConnect B Series FCX Configuration Guide ...
Страница 136: ...94 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Viewing information about software licenses 4 ...
Страница 228: ...186 PowerConnect B Series FCX Configuration Guide 53 1002266 01 PowerConnect B Series FCX hitless stacking 5 ...
Страница 229: ...PowerConnect B Series FCX Configuration Guide 187 53 1002266 01 PowerConnect B Series FCX hitless stacking 5 ...
Страница 230: ...188 PowerConnect B Series FCX Configuration Guide 53 1002266 01 PowerConnect B Series FCX hitless stacking 5 ...
Страница 248: ...206 PowerConnect B Series FCX Configuration Guide 53 1002266 01 IPv6 management commands 7 ...
Страница 346: ...304 PowerConnect B Series FCX Configuration Guide 53 1002266 01 802 1s Multiple Spanning Tree Protocol 8 ...
Страница 374: ...332 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Jumbo frame support 9 ...
Страница 424: ...382 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Virtual Switch Redundancy Protocol VSRP 10 ...
Страница 568: ...526 PowerConnect B Series FCX Configuration Guide 53 1002266 01 CLI examples 14 ...
Страница 588: ...546 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Sample application 15 ...
Страница 674: ...632 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Enabling or disabling layer 2 switching 19 ...
Страница 684: ...642 PowerConnect B Series FCX Configuration Guide 53 1002266 01 VLAN based mirroring 20 ...
Страница 724: ...682 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Reading CDP packets 23 ...
Страница 768: ...726 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Clearing cached LLDP neighbor information 24 ...
Страница 930: ...888 PowerConnect B Series FCX Configuration Guide 53 1002266 01 26 ...
Страница 948: ...906 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Configuring MLD snooping 27 ...
Страница 962: ...920 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Displaying CPU utilization statistics 28 ...
Страница 1022: ...980 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Displaying OSPF information 29 ...
Страница 1142: ...1100 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Clearing diagnostic buffers 30 ...
Страница 1258: ...1216 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Using Secure copy with SSH2 33 ...
Страница 1314: ...1272 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Displaying port security information 35 ...
Страница 1348: ...1306 PowerConnect B Series FCX Configuration Guide 53 1002266 01 Example configurations 36 ...
Страница 1406: ...1364 PowerConnect B Series FCX Configuration Guide 53 1002266 01 IP source guard 39 ...
Страница 1422: ...1380 PowerConnect B Series FCX Configuration Guide 53 1002266 01 SNMP v3 Configuration examples 40 ...