|
PPP can be used over what physical WAN interfaces?
PPP can be used on the following:
- Asynchronous serial interfaces
- High-Speed Serial Interface (HSSI)
- ISDN
- Synchronous serial interfaces
PPP is a data link layer protocol that provides network-layer services. What are the two sublayers of PPP?
The two sublayers of PPP are the following:
- Network Core Protocol (NCP) is the component that encapsulates
and configures multiple network layer protocols. Some examples<
of these protocols are IPCP (IP Control Protocol) and IPXCP
(Internetwork Packet Exchange Control Protocol).
- Link Control Protocol (LCP) is used to establish, configure,
maintain, and terminate PPP connections.
What features does LCP offer to PPP encapsulation?
LCP offers authentication, callback, compression, error detection, and multilink to PPP encapsulation.
The two methods of authentication on PPP links are:
- Password Authentication Protocol (PAP)
- Challenge Handshake Authentication Protocol (CHAP)
PAP is the less-secure of the two methods; passwords are sent in clear text and are exchanged only upon initial link establishment.
CHAP is used upon initial link establishment and periodically to make sure that the router is still communicating with the same host. CHAP passwords are exchanged as MD5 encrypted values.
What two protocols are available for compression on PPP links?
The two protocols available for compression are Stacker and Predictor.
What three phases are used to establish a PPP session?
The three phases used to establish a PPP session are the following:
- Step 1. Link establishment--Each PPP device sends LCP packets
to configure and test the link (Layer 1).
- Step 2. Authentication phase (optional)--If authentication is
configured, either PAP or CHAP is used to authenticate
the link. Authentication must take place before the
network layer protocol phase can begin (Layer 2).
- Step 3. Network layer protocol phase--PPP sends NCP packets to
choose and configure one or more network layer protocols
to be encapsulated and sent over the PPP data link
(Layer 3).
Note on authentication: Hostname and passwords are case-sensitive.
How do you enable PPP encapsulation on a Cisco router serial interface?
To enable PPP encapsulation on a serial interface, enter the encapsulation ppp interface command:
RouterB(config-if)#encapsulation ppp
How do you enable PPP authentication using PAP or CHAP on a Cisco router?
To enable PPP authentication on a Cisco router, follow these steps:
- Step 1. Make sure that each router has a host name assigned to
it using the hostname command.
- Step 2. On each router, define the username of the remote router
and password that both routers will use with the
username name password password command.
- Step 3. Configure PPP authentication with the ppp authentication
{chap | chap pap | pap chap | pap} interface command.
(If both PAP and CHAP are enabled, the first method you
specify in the command is used. If the peer suggests the
second method or refuses the first method, the second
method is used.)
For example:
RouterB(config)#hostname RouterB
RouterB(config)#username RouterA password cisco
RouterB(config)#int s0
RouterB(config-if)#ppp authentication chap pap
If PPP is enabled on an interface, how do you view the LCP and NCP states of the interface?
To view the LCP and NCP states of an interface, issue the show interface serial interface-number command:
RouterA#show int s0
Serial0 is up, line protocol is up
Hardware is HD64570
Internet address is 192.168.1.2/24
MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 1/255
Encapsulation PPP, loopback not set, keepalive set (10sec)
LCP Open
Open: IPCP, CDPCP
Last input 00:00:02, output 00:00:02, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0 (size/max/drops); Total output drops: 0
Queueing strategy: weighted fair
Output queue: 0/1000/64/0 (size/max total/threshold/drops)
Conversations 0/1/256 (active/max active/max total)
Reserved Conversations 0/0 (allocated/max allocated)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
675 packets input, 39555 bytes, 0 no buffer
Received 631 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
818 packets output, 48431 bytes, 0 underruns
0 output errors, 0 collisions, 13 interface resets
0 output buffer failures, 0 output buffers swapped out
36 carrier transitions
DCD=up DSR=up DTR=up RTS=up CTS=up
What is the default bandwidth on a serial interface on a Cisco router?
With the show interface serial 0 output: BW 1544
or 1.544 mbps or T1 (telco link).
What is the default encapsulation on a Cisco serial interface?
HDLC
|