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Chapter 24 IP Source Guard
GS2200-48 User’s Guide
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24.1.1 DHCP Snooping Overview
Use DHCP snooping to filter unauthorized DHCP packets on the network and to
build the binding table dynamically. This can prevent clients from getting IP
addresses from unauthorized DHCP servers.
24.1.1.1 Trusted vs. Untrusted Ports
Every port is either a trusted port or an untrusted port for DHCP snooping. This
setting is independent of the trusted/untrusted setting for ARP inspection. You can
also specify the maximum number for DHCP packets that each port (trusted or
untrusted) can receive each second.
Trusted ports are connected to DHCP servers or other switches. The Switch
discards DHCP packets from trusted ports only if the rate at which DHCP packets
arrive is too high. The Switch learns dynamic bindings from trusted ports.
Note: The Switch will drop all DHCP requests if you enable DHCP snooping and there
are no trusted ports.
Untrusted ports are connected to subscribers. The Switch discards DHCP packets
from untrusted ports in the following situations:
• The packet is a DHCP server packet (for example, OFFER, ACK, or NACK).
• The source MAC address and source IP address in the packet do not match any
of the current bindings.
• The packet is a RELEASE or DECLINE packet, and the source MAC address and
source port do not match any of the current bindings.
• The rate at which DHCP packets arrive is too high.
24.1.1.2 DHCP Snooping Database
The Switch stores the binding table in volatile memory. If the Switch restarts, it
loads static bindings from permanent memory but loses the dynamic bindings, in
which case the devices in the network have to send DHCP requests again. As a
result, it is recommended you configure the DHCP snooping database.
The DHCP snooping database maintains the dynamic bindings for DHCP snooping
and ARP inspection in a file on an external TFTP server. If you set up the DHCP
snooping database, the Switch can reload the dynamic bindings from the DHCP
snooping database after the Switch restarts.
Summary of Contents for GS2200-48
Page 2: ......
Page 8: ...Safety Warnings GS2200 48 User s Guide 8 ...
Page 22: ...22 ...
Page 28: ...Chapter 1 Getting to Know Your Switch GS2200 48 User s Guide 28 ...
Page 32: ...Chapter 2 Hardware Installation and Connection GS2200 48 User s Guide 32 ...
Page 40: ...40 ...
Page 62: ...Chapter 6 System Status and Port Statistics GS2200 48 User s Guide 62 ...
Page 76: ...Chapter 7 Basic Setting GS2200 48 User s Guide 76 ...
Page 78: ...78 ...
Page 102: ...Chapter 9 Static MAC Forward Setup GS2200 48 User s Guide 102 ...
Page 122: ...Chapter 11 Spanning Tree Protocol GS2200 48 User s Guide 122 ...
Page 126: ...Chapter 12 Bandwidth Control GS2200 48 User s Guide 126 ...
Page 148: ...Chapter 17 Port Security GS2200 48 User s Guide 148 ...
Page 156: ...Chapter 18 Classifier GS2200 48 User s Guide 156 ...
Page 164: ...Chapter 19 Policy Rule GS2200 48 User s Guide 164 ...
Page 214: ...Chapter 24 IP Source Guard GS2200 48 User s Guide 214 Figure 98 DHCP Snooping ...
Page 236: ...236 ...
Page 270: ...270 ...
Page 278: ...Chapter 31 Maintenance GS2200 48 User s Guide 278 ...
Page 304: ...Chapter 34 Syslog GS2200 48 User s Guide 304 ...
Page 312: ...Chapter 35 Cluster Management GS2200 48 User s Guide 312 ...
Page 316: ...Chapter 36 MAC Table GS2200 48 User s Guide 316 ...
Page 320: ...Chapter 37 IP Table GS2200 48 User s Guide 320 ...
Page 324: ...Chapter 39 Routing Table GS2200 48 User s Guide 324 ...
Page 327: ...327 PART VI Product Specifications Product Specifications 329 ...
Page 328: ...328 ...
Page 336: ...Chapter 41 Product Specifications GS2200 48 User s Guide 336 ...
Page 338: ...338 ...
Page 352: ...Appendix B Legal Information GS2200 48 User s Guide 352 ...
Page 362: ...Index GS2200 48 User s Guide 362 ...