13 - Implementing Pt to Pt WANS Flashcards
What is CPE?
Customer Premise Equipment
What does CSU/DSU stand for?
Channel Service Unit / Data Service Unit
What does a CSU/DSU do?
Provides clocking on the line controlling the speed and timing that the router can send each bit over the line
What is the bit rate for a DS0?
64 Kbps
What is another name for DS1?
T1
What is the bit rate for a T1?
1.544 Mbps
What multiples make up a Fractional T1?
Multiples of 64 Kbps
What multiples make up a Fractional T3?
Multiples of 1.536 Mbps
What is the bit rate for a T3?
44.736 Mbps
What does DCE stand for?
Data Circuit-terminating Equipment
What does the DCE funtion do?
Controls the speed of the router’s serial interface
What does DTE stand for?
Data Terminal Equipment
What does the DTE do?
DTE is the router that is controlled by the DCE
How is Cisco’s HDLC protocol different that ISO’s HDLC?
Cisco adds a Type field that allows the serial line to support multiple types of network layer packets
What are the 6 fields in a Cisco HDLC frame?
- Flag
- Address
- Control
- Type
- Data
- FCS
What are 2 ways to enable HDLC encapsulation on an interface?
- ‘no encapsulation’ cmd to return to default HDLC or
- encapsulation HDLC
What 2 ‘show’ commands that confirm a serial link has been successfully installed?
- show controllers s0/0/0
- show interfaces s0/0/0
What 5 things does PPP provide?
- defines a header and trailer
- supports both synchronous and asynchronous
- Protocol Type field allowing multiple layer 3 protocols
- Built-in authentication tools
- control protocols for each higher-layer protocol riding over PPP
In PPP frame what does the Type field do?
Identifies which L3 protocol is in the frame
in PPP what are the 2 categories of Control Protocols?
- Link Control Protocols (LCP)
- Network Control Protocols (NCP)
What are 3 examples of NCPs?
- IPCP
- IPv6CP
- CDPCP
What are 4 LCPs?
- Looped Link Detection
- Error Detection
- Multilink Support
- Authentication
In PPP what are the 2 Authentication protocols?
- PAP
- CHAP
How does the PAP authentication process work?
- The router wanting to be authenticated - R2 - starts the conversation
- R2 tells R1 username and password in clear text
- R1 Acknowledges auth successful
How does the CHAP process work?
- The router doing the authenticating - R1 - initiates
- R1 sends challenge that includes a Random Number to R2
- R2 replies with a MD5 Hash created from the Random Number and the Password
- R1 acknowledges auth successful
In PPP CHAP what does the Challenging router do if authentication fails?
Leaves interface in Up/Down state
What kind of Hash does PPP CHAP use?
MD5
What is the command to enable PPP on an interface?
encapsulation ppp
What show command verifies that PPP has been enabled?
- show interfaces s0/0/0
- will show encapsulation ppp
- also LCP Open
- also Open: IPCP, CDPCP
What configuration steps are needed on router1 to configure CHAP?
- encapsulation ppp
- hostname router1
- username router2 password letmein
- interface s0/0/0
- ppp authentication chap
What configuration steps are needed on router2 to configure CHAP?
- encapsulation ppp
- hostname router2
- username router1 password letmein
- interface s0/0/0
- ppp authentication chap
When configuring PPP CHAP which two parameters need to match?
- username on local router must match hostname on remote router
- passwords must be the same
What show command confirms authentication succeeded?
- show ppp all
- should show ‘+’ for every protocol that succeeded
When configuring PPP PAP which parameters need to match?
- interface s0/0
- ppp pap sent-username r1 password test
- must match username r1 password test on remote router
What ‘show’ command will show if PAP authentication worked?
* show ppp all * should show ‘+’ for every protocol that succeeded
What configuration steps are needed to configure PAP?
* interface subcommands * encapsulation ppp * ppp authentication pap * ppp pap sent-username r1 password test * then on remote router username r1 password test
What command will tell a router to try CHAP first and if that doesn’t succeed try PAP
* ppp authentication chap pap
Which layer does MLPPP load balance at?
Layer 2
Which 2 ‘show’ commands verify MLPPP is working?
* show interfaces multilink 1 * show ppp multilink
What does an interface state of down/down indicate?
a problem at layer 1
What does an interface state of up/down indicate?
a problem at layer 2
What does an interface state of up/up indicate?
layer 3 is working
What are some possible causes of interfaces in down/down state?
* cable unplugged * bad cable * broken CSU * problem at telco
What could be the problem when interfaces are up/down flapping on both ends?
Mismatched encapsulation commands
What could be the problem if one side is up/down and the other side is up/up?
Keepalives disabled on the up/up side
What could be the problem when interfaces are up/down on both ends but NO Flapping?
PAP or CHAP Authentication Failure
How often are keepalives sent to the remote router by default?
once every 10 seconds
What debug command will help diagnose a PPP Authentication Failure?
debug ppp authentication
