826
C
HAPTER
60: DHCP S
NOOPING
C
ONFIGURATION
configured as trusted or untrusted, ensuring the clients to obtain IP addresses from
authorized DHCP servers.
■
Trusted: A trusted port forwards DHCP messages, ensuring that DHCP clients
can obtain valid IP addresses.
■
Untrusted: The DHCP-ACK or DHCP-OFFER packets received from an untrusted
port are discarded, preventing DHCP clients from receiving invalid IP addresses.
Application
Environment of Trusted
Ports
Configuring a trusted port connected with a DHCP server
A port that is connected with a DHCP server directly or indirectly should be
configured as a trusted port, so that the DHCP snooping device can forward reply
messages from the DHCP server, ensuring the DHCP clients to obtain IP addresses
from the authorized DHCP server.
As shown in Figure 250, GE1/0/1 on Switch B is connected with Switch A (a DHCP
server). GE1/0/1 should be configured as a trusted port, so that it can forward
replies from Switch A.
Figure 250
Configure a trusted port connected with the DHCP sever
Configuring trusted ports in a cascaded network
In a cascaded network involving multiple DHCP snooping devices, the ports
connected to other DHCP snooping devices should be configured as trusted ports.
To save system resources, you can disable the trusted ports, which are indirectly
connected with DHCP clients, from recording clients’ IP-to-MAC bindings.
As shown in Figure 251, Switch A, Switch B, and Switch C are DHCP snooping
devices. GE1/0/2 and GE1/0/3 on Switch A, GE1/0/1 and GE1/0/2 on Switch B, and
GE1/0/2, GE1/0/3, and GE1/0/4 on Switch C are configured as trusted ports.
Disable the trusted ports, GE1/0/3 on Switch A, GE1/0/1 on Switch B, GE1/0/3 and
GE1/0/4 on Switch C, which are not directly connected to DHCP clients, from
recording client’s IP-to-MAC bindings.
GE1/0/1
Switch A
DHCP server
Switch B
DHCP snooping
GE1/0/2
DHCP client
DHCP client
GE 1/0 /3
Summary of Contents for 4800G Series
Page 26: ...26 CHAPTER NETWORKING APPLICATIONS ...
Page 30: ...30 CHAPTER 1 LOGGING IN TO AN ETHERNET SWITCH ...
Page 62: ...62 CHAPTER 3 LOGGING IN THROUGH TELNET ...
Page 70: ...70 CHAPTER 5 LOGGING IN THROUGH WEB BASED NETWORK MANAGEMENT SYSTEM ...
Page 72: ...72 CHAPTER 6 LOGGING IN THROUGH NMS ...
Page 82: ...82 CHAPTER 8 CONTROLLING LOGIN USERS ...
Page 98: ...98 CHAPTER 9 VLAN CONFIGURATION ...
Page 108: ...108 CHAPTER 10 VOICE VLAN CONFIGURATION ...
Page 119: ...GVRP Configuration Examples 119 DeviceB display vlan dynamic No dynamic vlans exist ...
Page 120: ...120 CHAPTER 11 GVRP CONFIGURATION ...
Page 160: ...160 CHAPTER 17 PORT ISOLATION CONFIGURATION ...
Page 172: ...172 CHAPTER 19 LINK AGGREGATION CONFIGURATION ...
Page 196: ...196 CHAPTER 22 DLDP CONFIGURATION ...
Page 240: ...240 CHAPTER 23 MSTP CONFIGURATION ...
Page 272: ...272 CHAPTER 27 RIP CONFIGURATION ...
Page 364: ...364 CHAPTER 29 IS IS CONFIGURATION ...
Page 426: ...426 CHAPTER 31 ROUTING POLICY CONFIGURATION ...
Page 442: ...442 CHAPTER 33 IPV6 RIPNG CONFIGURATION ...
Page 466: ...466 CHAPTER 35 IPV6 IS IS CONFIGURATION ...
Page 488: ...488 CHAPTER 36 IPV6 BGP CONFIGURATION ...
Page 498: ...498 CHAPTER 37 ROUTING POLICY CONFIGURATION ...
Page 540: ...540 CHAPTER 40 TUNNELING CONFIGURATION ...
Page 552: ...552 CHAPTER 41 MULTICAST OVERVIEW ...
Page 604: ...604 CHAPTER 43 MLD SNOOPING CONFIGURATION ...
Page 628: ...628 CHAPTER 46 IGMP CONFIGURATION ...
Page 700: ...700 CHAPTER 48 MSDP CONFIGURATION ...
Page 812: ...812 CHAPTER 57 DHCP SERVER CONFIGURATION ...
Page 822: ...822 CHAPTER 58 DHCP RELAY AGENT CONFIGURATION ...
Page 834: ...834 CHAPTER 61 BOOTP CLIENT CONFIGURATION ...
Page 850: ...850 CHAPTER 63 IPV4 ACL CONFIGURATION ...
Page 856: ...856 CHAPTER 64 IPV6 ACL CONFIGURATION ...
Page 860: ...860 CHAPTER 65 QOS OVERVIEW ...
Page 868: ...868 CHAPTER 66 TRAFFIC CLASSIFICATION TP AND LR CONFIGURATION ...
Page 888: ...888 CHAPTER 69 PRIORITY MAPPING ...
Page 894: ...894 CHAPTER 71 TRAFFIC MIRRORING CONFIGURATION ...
Page 904: ...904 CHAPTER 72 PORT MIRRORING CONFIGURATION ...
Page 930: ...930 CHAPTER 74 UDP HELPER CONFIGURATION ...
Page 990: ...990 CHAPTER 79 FILE SYSTEM MANAGEMENT CONFIGURATION ...
Page 1000: ...1000 CHAPTER 80 FTP CONFIGURATION ...
Page 1020: ...1020 CHAPTER 82 INFORMATION CENTER CONFIGURATION ...
Page 1038: ...1038 CHAPTER 84 SYSTEM MAINTAINING AND DEBUGGING ...
Page 1046: ...1046 CHAPTER 85 DEVICE MANAGEMENT ...
Page 1129: ...SSH Client Configuration Examples 1129 SwitchB ...
Page 1130: ...1130 CHAPTER 88 SSH CONFIGURATION ...
Page 1160: ...1160 CHAPTER 90 RRPP CONFIGURATION ...
Page 1180: ...1180 CHAPTER 91 PORT SECURITY CONFIGURATION ...
Page 1192: ...1192 CHAPTER 92 LLDP CONFIGURATION ...
Page 1202: ...1202 CHAPTER 93 POE CONFIGURATION ...
Page 1218: ...1218 CHAPTER 96 HTTPS CONFIGURATION ...