Wrong Dhcp Snooping Networking Examples - H3C S9500 Series Operation Manual

Operation Manual – DHCP
H3C S9500 Series Routing Switches
Note:
To ensure the DHCP client to obtain an IP address from the DHCP server, you need to
complete other configurations on the DHCP client and DHCP server. The configuration
procedure is omitted because it varies depending on the device model.

4.5 Wrong DHCP Snooping Networking Examples

The DHCP snooping enabled device can work when it is between the DHCP client and
server or between the DHCP client and relay agent. It does not work if it is between the
DHCP server and DHCP relay agent.
The following shows two wrong DHCP snooping networking examples.
I. Wrong DHCP networking example I
Figure 4-2 Network diagram for a wrong DHCP snooping network
In Figure
server.
In this network, because the source and destination UDP port numbers in DHCP
packets exchanged between the DHCP relay agent and DHCP server are both 67, the
DHCP snooping device cannot judge the sender of DHCP packets. Moreover, because
the port on the DHCP snooping device that is connected to the DHCP relay agent is an
untrusted port, DHCP request packets sent by the DHCP relay agent cannot be
forwarded to the DHCP server. Thus, no DHCP snooping entry can be generated on
the DHCP snooping device.
II. Wrong DHCP networking example II
Figure 4-3 Network diagram for a wrong DHCP snooping network
In Figure
device.
In this network, the DHCP snooping device obtains DHCP request and reply packets
from the port connected to the DHCP server. Thus, no DHCP snooping entry can be
generated on the DHCP snooping device.
4-2, the DHCP snooping device is between the DHCP relay agent and DHCP
4-3, the DHCP server is between the DHCP client and DHCP snooping
Chapter 4 DHCP Snooping Configuration
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