Mypower
S4100
Troubleshooting
Maipu Confidential & Proprietary Information
Page
75
of
124
Possible Reasons
Judging Methods and Solutions
Other DHCP function is
enabled.
DHCP SNOOPING is between DHCP Server and DHCP Client. If
other DHCP function is enabled on the device, for example,
DHCP Server or DHCP Client (the L3 interface is distributed
with IP address via DHCP) and DHCP Relay is enabled, DHCP
SNOOPING cannot be enabled. Therefore, to configured the
device as DHCP SNOOPING, clear up other DHCP configuration.
Fault 2: DHCP client cannot get IP address.
Possible Reasons
Judging Methods and Solutions
The port connecting DHCP
SNOOPING and DHCP
Server is not set as the trust
port.
After enabling DHCP SNOOPING, all ports are dhcp untrust
ports by default. You need to set the port connecting DHCP
SNOOPING and DHCP Server as the trust port. Otherwise, the
offer packets sent by DHCP Server are dropped directly and the
client cannot get the IP address.
The dhcp-snooping option
82 function is enabled, but
dhcp-snooping relay-address
is not configured.
After enabling OPTION 82, some servers may need to carry
relay address in the packet. The address must be configured as
the IP address that can intercommunicate with the DHCP
server on the device and the L3 interface of the address must
be in the same VLAN as the client and server ports. Use the
dhcp-snooping relay-address command to specify the
address.
The attack detection
function is enabled and the
DHCP packets are filtered.
Some unnecessary attack detection functions are disabled, such
as ip fraggle intercept.
Fault 3: The port cannot be shutdown by the err-disable function.
Possible Reasons
Judging Methods and Solutions
The packets received by the
port do not exceed the
threshold in successive 20s.
After enabling DHCP SNOOPING in the global configuration
mode, the DHCP packet rate of the dhcp untrust port is limited
as 40pps by default (the value can be modified in the port
configuration mode via the dhcp-snooping rate-limit
command). The port can be shutdown by err-disable only when
the received DHCP packets exceed the limitation in successive
20s. Confirm that the DHCP packets received by the port
exceed the limitation in more than successive 20s. If necessary,
set the rate limitation of the DHCP packets as one smaller
value.
Fault 4: The port cannot become up after being shutdown by err-disable
because the received DHCP packets exceeds the limitation.
Possible Reasons
Judging Methods and Solutions
The errdisable recovery
function is not enabled.
After the port is shutdown by err-disable because the received
DHCP packets exceeds the limitation, you need to execute the
command errdisable recovery cause dhcp-snooping in the
