Troubleshooting guide

Tip: If you are not familiar with configuring Cisco devices and would like to follow a step−by−step
configuration, click here.
Tasks to Perform
Note: A color code is used to relate tasks in this section with examples of configurations in the Configuration
section. Configurations are color−coded as follows: Dynamic Host Configuration Protocol (DHCP) Server,
Network Address Translation (NAT).
Design an IP addressing scheme for your private LAN.•
Configure an IP address, subnet mask, and TCP maximum segment size (MSS) adjustment on the
Cisco DSL Router Ethernet interface.
•
Configure the ATM interface (Asymetric Digital Subscriber Line (ADSL) interface) of the Cisco DSL
Router with an ATM permanent virtual circuit (PVC) and encapsulation.
•
Configure a Point−to−Point Protocol over Ethernet (PPPoE) virtual private data network (VPDN)
group for Cisco IOS®Software older than 12.2(13)T.
.
•
Create and configure the Dialer interface of the Cisco DSL Router for PPPoE with a negotiated IP
address.
•
Configure NAT on the Cisco DSL Router to allow sharing of the dynamic public IP address of the
Dialer interface.
•
Optional: NAT Pool, if additional IP addresses have been provided by your ISP.♦
Optional: Static NAT, if Internet users require access to internal servers.♦
Configure each PC client with an IP address, subnet mask, default gateway, and Domain Name
System (DNS) server(s).
Alternatively, if you want the Cisco DSL Router to assign your PC clients' dynamic IP addresses,
configure each PC to obtain an IP address and DNS server(s) automatically via DHCP.
•
Possible Required Configuration Steps on the PC
If your Cisco DSL Router software supports the ip tcp adjust−mss 1452 or ip adjust−mss
1452 configuration commands, no further action is needed and you can continue with the Configuration
section.
If your Cisco DSL Router software does not support the ip tcp adjust−mss 1452 or ip
adjust−mss 1452 configuration commands, you must change the maximum transmission unit (MTU)
size on each PC in your LAN that will have access to the Internet through the Cisco DSL Router. To change
the MTU size, follow the steps below.
Download the latest version of the Dr. TCP utility from http://www.dslreports.com/front/drtcp.html.1.
Refresh your browser page to ensure the page is current.2.
Run the Dr. TCP utility.3.
From the menu choose your Ethernet adapter.4.
Cisco DSL Router Configuration and Troubleshooting Guide