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C
HAPTER
7
| Security Measures
DHCP Snooping
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information fields to describe itself) can be identified in the DHCP
request packets forwarded by the switch and in reply packets sent back
from the DHCP server. This information may specify the MAC address or
IP address of the requesting device (that is, the switch or port to which
the client is connected in this context).
By default, the switch also fills in the Option 82 circuit-id field with
information indicating the local interface over which the switch received
the DHCP client request, including the port and VLAN ID. This allows
DHCP client-server exchange messages to be forwarded between the
server and client without having to flood them to the entire VLAN.
If DHCP Snooping Information Option 82 is enabled on the switch,
information may be inserted into a DHCP request packet received over
any VLAN (depending on DHCP snooping filtering rules). The
information inserted into the packets includes the circuit-id and
remote-id, as well as the gateway Internet address.
When the switch receives DHCP packets from clients that already
include DHCP Option 82 information, the switch can be configured to
set the action policy for these packets. The switch can either drop the
DHCP packets, keep the existing information, or replace it with the
switch’s relay information.
DHCP snooping must be enabled for the DHCP Option 82 information to
be inserted into packets. When enabled, the switch will only add/
remove option 82 information in incoming DCHP packets but not relay
them. Packets are processed as follows:
If an incoming packet is a DHCP request packet with option 82
information, it will modify the option 82 information according to
settings specified with by the DHCP snooping information policy.
If an incoming packet is a DHCP request packet without option 82
information, enabling the DHCP snooping information option will
add option 82 information to the packet.
If an incoming packet is a DHCP reply packet with option 82
information, enabling the DHCP snooping information option will
remove option 82 information from the packet.
P
ARAMETERS
These parameters are displayed:
DHCP Snooping Information Option Status
– Enables or disables
DHCP Option 82 information. (Default: Disabled)
DHCP Snooping Information Option 82 Sub-option Format
–
Enables or disables use of sub-type and sub-length fields in circuit-ID
(CID) and remote-ID (RID) in Option 82 information.
(Default: Enabled)
Содержание DG-FS4528P
Страница 2: ......
Страница 4: ......
Страница 148: ...CHAPTER 5 Simple Network Management Protocol Configuring SNMPv3 Groups 148 ...
Страница 279: ...CHAPTER 8 Interface Configuration Showing Port or Trunk Statistics 279 Figure 130 Showing Port Statistics ...
Страница 289: ...CHAPTER 10 Address Table Settings Changing the Aging Time 289 4 Click Apply Figure 137 Setting the Address Aging Time ...
Страница 389: ...CHAPTER 17 VoIP Traffic Configuration Configuring Telephony OUI 389 ...
Страница 414: ...CHAPTER 18 Multicast Filtering Multicast VLAN Registration 414 Figure 216 Configuring Static MVR Receiver Group Members ...
Страница 515: ...CHAPTER 22 System Management Commands UPnP 515 TTL 20 Console ...
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Страница 973: ...DG FS4528P ...