When would you need this: When you are
creating a WAN link.
And also when the other end of a WAN link is NOT a Cisco router.
Protocol can be used in synchronous, asynchoronous, HSSI, and ISDN
Special Requirements: None.
1. Get to the interface configuration mode and issue the
2. If you want to configure authentication (which is
always the case), go through the following steps:
a. Choose the authentication type; Password
Protocol (PAP), or Challenge Handshake Authentication Protocol (CHAP).
XXX is the
authentication type which can be:
pap chap, or
pap. The last two choices are to use the other
authentication type when the first one fails.
CHAP is strongly recommended over PAP for two reasons.
PAP sends the username and password in plaintext, while CHAP sends
challenges only. Second is that CHAP does an operation similar to
re-authentication in the middle of the communication session such that
provides more security than PAP.
b. Set a username and a password that the remote router
would use to connect to your local router. You can define many
username-password pairs for many PPP connections to the same router.
USER is the
host name of the remote router, and
is its password. Issue this command once for each PPP connection. For
if you are connecting RouterA to RouterB and RouterC, on RouterA issue
command once for each remote router.
c. Now you can set the username and password that you local router would
use to access the remote router. F
authentication, you can
specify the username and password that the local router will send to
the remote router for authentication using the following command,
sent-username USER passwrod PASS
For CHAP, two commands are used,
chap hostname USER
chap password PASS
The usernames and passwords are case sensitive, so be
careful when writing them. This way, you will have to write the hostname
and secret password of the remote router in your local router and write
the hostname and secret password of your local router into your remote
using the '
If you do not set the username and password that will be sent from the
local router to the remote router for authentication, the router will
use its hostname and secret password instead.
3. You can monitor the quality of the serial link that is
using PPP with the following command,
the minimum accepted link quality. If the
link quality drops below
the link will be shutdown and considered bad.
4. If the available bandwidth is small, you might
compressing the data being transmitted using the following command,
YYY is the
compression type which can be predictor or
Note: The compression might affect the
because it increases the CPU load. Check the CPU load with ‘
show process cpu’
and disable the compression if the CPU load is over 65%.
5. To troubleshoot PPP, you can use the following