Cisco Catalyst 4500 Series, Software Configuration Manual

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Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
Chapter 60 Configuring DHCP Snooping, IP Source Guard, and IPSG for Static Hosts
About DHCP Snooping
In the default suboption configuration, when the described sequence of events occurs, the values in these
fields in
Figure 60-2 do not change:
• Circuit ID suboption fields
–
Suboption type
– Length of the suboption type
–
Circuit ID type
– Length of the circuit ID type
•
Remote ID suboption fields
– Suboption type
–
Length of the suboption type
– Remote ID type
–
Length of the remote ID type
Figure 60-2 shows the packet formats for the remote ID suboption and the circuit ID suboption when the
default suboption configuration is used. For the circuit ID suboption, the module number corresponds to
the switch module number. The switch uses the packet formats when you globally enable DHCP
snooping and enter the
ip dhcp snooping information option global configuration command.
Figure 60-2 Suboption Packet Formats
Figure 60-3 shows the packet formats for user-configured remote ID and circuit ID suboptions. The
switch uses these packet formats when DHCP snooping is globally enabled and when the ip dhcp
snooping information option format remote-id global configuration command and the ip dhcp
snooping vlan information option format-type circuit-id string interface configuration command are
entered.
Length Length
Circuit
ID type
Suboption
type
Circuit ID S uboption Frame Format
Remote ID S uboption Frame Format
6 bytes
MAC address
1 byte 1 byte 1 byte
Suboption
type
1 byte
Length Length
Remote
ID type
1 byte 1 byte 1 byte 1 byte
116300
4 0 6 1
6 0 8 2
Module Port
1 byte 1 byte 2 bytes
VLAN