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Knowledge Base

Dialing up to the Headquarters through the L2TP and then Accessing the Internet through the Headquarters Network

Publication Date:  2012-07-25  |   Views:  145  |   Downloads:  0  |   Author:  anliku  |   Document ID:  EKB1000012803


Issue Description

A customer accesses the Internet through Tietong, dials up to the headquarters, and attempts to access the Internet through the headquarters network. However, after dialing up to the headquarters, the customer can access intranet resources of the headquarters, but cannot normally access the Internet.

Alarm Information


Handling Process

1. Check whether the customer can normally dial up and access the headquarters resources. The result is normal.
2. Check whether all customer data goes through the VPN tunnel. The result is normal.
3. Check whether the customer accesses the Internet sessions on the egress firewall at headquarters. The result shows that there are only translated sessions, but the headquarters intranet can be normally accessed. This indicates that the link works properly.
4. Check the IP address that is obtained by the customer. No DNS is obtained. As a result, the customer fails to access the Internet.
5. Configure the DNS on the client manually. The customer can normally access the Internet.

Root Cause

The customer applies the route to the virtual template. NAT is not performed. All data goes through the L2TP VPN, but the customer cannot obtain the DNS when the IP address of the VPN is obtained. As a result, the customer cannot normally access the Internet.


The problem occurs because the VPN client can only obtain the IP address, but not the DNS.