[All About Switches] A PC Fails to Obtain an IP Address from the Switch Connected to It

Involved Products and Versions

All products and versions

Networking

As shown in Figure 1-1, the switch is connected to the PC through the interface GE1/0/1 that is configured as an access interface. The DHCP server is configured on the switch to dynamically assign IP addresses to the PC.

Figure 1-1 Networking diagram of the failure of the PC to obtain an IP address from the switch connected to it

Fault Symptom

The PC fails to obtain an IP address.

Cause Analysis

Check the configurations on the interface GE1/0/1. It is found that remark 8021p is configured. If the interface is an access interface, the access interface removes the VLAN tag from the outbound packets. Therefore, when the remark 8021p command is run in the outbound direction, the packet contents are modified. As a result, the forwarded DHCP packets are incorrect packets. Therefore, the PC fails to obtain an IP address.

#
acl number 4000
 rule 5 permit destination-mac e411-5b50-43dd
traffic classifier TV operator and
 if-match acl 4000
traffic behavior TV
 remark 8021p 4
traffic policy TV
 classifier TV behavior TV
interface GigabitEthernet1/0/1
 traffic-policy TV outbound
#

Troubleshooting Procedure

Delete the remark 8021p 4 configuration from the switch. The PC can then obtain an IP address.

Conclusions and Suggestions

If a traffic policy containing remark 8021p is applied to the outbound direction on an interface, the VLAN of the interface must work in tagged mode.