ZyXEL Communications GS2210-8 User Manual page 254

• The packet is a RELEASE or DECLI NE packet , and t he source MAC address and source port do not
m at ch any of t he current bindings.
• The rat e at which DHCP packet s arrive is t oo high.
26.19.1.2 DHCP Snooping Database
The Swit ch st ores t he binding t able in volat ile m em ory. I f t he Swit ch rest art s, it loads st at ic
bindings from perm anent m em ory but loses t he dynam ic bindings, in which case t he devices in t he
net work have t o send DHCP request s again. As a result , it is recom m ended you configure t he DHCP
snooping dat abase.
The DHCP snooping dat abase m aint ains t he dynam ic bindings for DHCP snooping and ARP
inspect ion in a file on an ext ernal TFTP server. I f you set up t he DHCP snooping dat abase, t he
Swit ch can reload t he dynam ic bindings from t he DHCP snooping dat abase aft er t he Swit ch
rest art s.
You can configure t he nam e and locat ion of t he file on t he ext ernal TFTP server. The file has t he
following form at :
Figure 176 DHCP Snooping Dat abase File Form at
<initial-checksum>
TYPE DHCP-SNOOPING
VERSION 1
BEGIN
<binding-1> <checksum-1>
<binding-2> <checksum-1-2>
...
...
<binding-n> <checksum-1-2-..-n>
END
The < init ial- checksum > helps dist inguish bet ween t he bindings in t he lat est updat e and t he
bindings from previous updat es. Each binding consist s of 72 byt es, a space, and anot her checksum
t hat is used t o validat e t he binding when it is read. I f t he calculat ed checksum is not equal t o t he
checksum in t he file, t hat binding and all ot hers aft er it are ignored.
26.19.1.3 DHCP Relay Option 82 Information
The Swit ch can add inform at ion t o DHCP request s t hat it does not discard. This provides t he DHCP
server m ore inform at ion about t he source of t he request s. The Swit ch can add t he following
inform at ion:
• Slot I D ( 1 byt e) , port I D ( 1 byt e) , and source VLA N I D ( 2 byt es)
• Syst em nam e ( up t o 32 byt es)
This inform at ion is st ored in an Agent I nform at ion field in t he opt ion 82 field of t he DHCP headers of
client DHCP request fram es. See
opt ion 82.
When t he DHCP server responds, t he Swit ch rem oves t he inform at ion in t he Agent I nform at ion field
before forwarding t he response t o t he original source.
You can configure t his set t ing for each source VLAN. This set t ing is independent of t he DHCP relay
set t ings ( Chapt er 40 on page
Chapter 26 IP Source Guard
Chapt er 40 on page 337
337) .
GS2210 Series User's Guide
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for m ore inform at ion about DHCP relay