Term
| What are the three (four) basic WAN connection types? |
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Definition
leased line
circuit switched
packet switched
(cell-switched)
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Term
| What are the characteristics (pros/cons) of a leased line WAN connection? |
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Definition
WAN connection for exclusive use of a customer. Uses synchronous serial interfaces.
Pros: Total control over traffic on circuit, easy to configure, best reliability
Cons: Expensive over long distance |
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Term
| What are the characteristics of a circuit-switched WAN connection? |
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Definition
Modems on both ends connected via asynchronous interfaces and ISDN technologies.
Circuit established using a telephone company |
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Term
| What are the characteristics of a packet-switched WAN connection? |
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Definition
Virtual circuit established on synchronous serial interfaces between two or more sites.
(Alternative to leased line with less cost.) |
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Term
| What WAN encapsulations are supported on leased lines and circuit-switched connections? (3) |
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Definition
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Term
| What WAN encapsulations are supported on a packet-switched connection? (3) |
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Definition
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Term
What kind of WAN connections are the following encapsulations supported on?
ATM
Frame Relay
HDLC
PPP
SLIP
X.25 |
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Definition
ATM: Packet switched
Frame Relay: Packet switched
HDLC: Leased line/circuit switched
PPP: Leased line/circuit switched
SLIP: Leased line/circuit switched
X.25: Packet switched |
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Term
What are the 3 major WAN protocols?
(Which of them is the default encapsulation on serial interfaces of Cisco devices?) |
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Definition
Frame Relay, PPP, HDLC
Cisco HDLC is default |
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Term
| What are the characteristics of PPP? |
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Definition
Point-to-point protocol
Encapsulates network layer protocols over point-to-point links |
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Term
| What are the sub-layers of PPP and what do they do? |
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Definition
NCP: Network Control Protocol
- Responsible for supporting L3 protocols, encapsulate them into PPP
LCP: Link Control Protocol
- Establishes the WAN link, negotiate optional settings (eg. authentication) |
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Term
| What are the 4 optional settings for PPP? |
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Definition
CCMA:
Compression - Stacker and Predictor options
Callback - used for centralized billing/security
Multilink - bundle more than one link for bandwidth
Authentication - CHAP and PAP options |
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Term
| What does PAP stand for and how does it work? |
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Definition
Password Authentication Protocol
Two way authentication process where the username and password is sent followed by a response message indicating success or fail. |
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Term
| What does CHAP stand for and how does it work? |
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Definition
Challenge Handshake Authentication Protocol
A username with the same password configured on both sides. One side performs three-way handshake at the start of a connection and every two minutes. MD5 hash used to mask the password.
1. ----Challenge--->
2. <---Response----
3. --Success/Fail--> |
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Term
| What are the steps for configuring authentication for PPP? (With fallback?) |
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Definition
1. Configure hostname and enable password/secret
2. Configure username (hostname of other device) and password list (passwords should match)
3. Enable PPP encapsulation: encapsulation ppp
4. Enable PAP or CHAP: ppp authentication pap/chap
With fallback: ppp authentication chap pap |
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Term
| What are the two types of Frame Relay virtual circuits and what are their characteristics? |
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Definition
Permanent Virtual Circuit (PVC) - always connected, like a leased line
Switched Virtual Circuit (SVC) - established only when needed. |
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Term
| What does DLCI stand for and what is it for? |
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Definition
Data-Link Connection Identifiers
Maps IP with frame relay circuit ends (locally significant) |
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Term
| What does LMI stand for and what does it do? |
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Definition
Local Management Interface
Used for status inquiries and reporting of the PVC
Also used as a keepalive mechanism |
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Term
| In frame relay, what are the three possible states of a PVC? |
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Definition
Active
Inactive (problem with remote end)
Deleted (problem between ends) |
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Term
| What are the three types of LMI that can be configured? |
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Definition
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Term
| For Frame Relay, what is CIR? |
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Definition
Committed Information Rate - guaranteed rate at which a particular PVC is allowed to pass data.
(If no congestion, burst rate is allowed to exceed CIR) |
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Term
| How is congestion managed over Frame Relay? (3) |
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Definition
Any traffic above CIR (Committed Info Rate) is marked with a DE (Discard Eligible) bit, and dropped.
FECN (Forward Explicit Congestion Notification) bit set on frames to receiving destination and requests some traffic to be sent back.
BECN bit set on returning frames to sender |
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Term
| What are the 2 methods that Frame Relay can use to map L3 address to DLCI? |
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Definition
static map command
or
inverse arp |
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Term
| What is the default setting for Frame Relay with regards to broadcast traffic? |
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Definition
| Frame Relay is by default Non-Broadcast Multi-Access |
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Term
| What are 4 possible solutions to the Split Horizon problem with point-to-multipoint Frame Relay connections? |
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Definition
Disable split horizon (no ip split-horizon)
Use fully meshed topology
Use static routes instead of dynamic routing
Use point-to-point subinterfaces instead of point-to-multipoint interfaces |
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Term
| What are the three main show commands to verify a Frame Relay connection? |
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Definition
show frame-relay lmi
- # of status inquiries/keepalives
show frame-relay pvc
- status of PVC, BECN/FECN messages
show frame-relay map
- status of PVC, IP-DLCI mapping |
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Term
What is the addressing requirement for multipoint frame relay router interfaces?
For point-to-point subinterfaces? |
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Definition
Multipoint: must all be on same subnet to forward routing updates and broadcasts
Point-to-Point: each subinterface connection on their own subnet |
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Term
| What command enables clocking when absent a DCE device? |
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Definition
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Term
| What are the characteristics of a cell-switched connection? |
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Definition
| Similar to packet switching (virtual circuits on synchronous serial), except that cell size is constant (as opposed to variable frame sizes) |
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Term
| What are required when configuring subinterfaces for frame relay? |
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Definition
IP addresses on subinterfaces only. Removed from physical interface.
Subinterface must specify point-to-point or multipoint. (No defaults.) |
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Term
| What's the command to statically map a frame relay link and where is it placed? |
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Definition
On the interface:
frame-relay map ip [NextHopIP] [LocalDLCI] (broadcast)
(broadcast keyword allows routing updates over PVC) |
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Term
| What are the two frame relay encapsulations (and which is default)? |
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Definition
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Term
What does CSU/DSU stand for and what does it do?
How does it differ from modem? |
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Definition
Channel Service Unit/Data Service Unit connects DTE devices (eg. routers) to a digital circuit (eg. T1 line).
Modem converts signals to an analog circuit (eg. phone line) |
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Term
| What are the reserved DLCI and what is it used for? |
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Definition
Reserved DLCI is for exchanging PVC status updates.
DLCI 0 - reserved for ANSI
DLCI 1023 - Manufacturer's LMI |
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Term
| What does PPPoE stand for and what is it for? |
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Definition
Point to Point Protocol over Ethernet
Authenticate/connect DSL connection to ISP |
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Term
| What are the 4 basic steps for configuring PPPoE? |
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Definition
1. On the physical interface, enable PPPoE and configure a dialer reference
2. Configure a dialer interface (Virtual LAN interface). Specify MTU & authentication (PAP/CHAP) info.
3. Configure PAT to map ACL of network to dialer interface.
4. Configure default route to dialer interface |
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Term
| What command can be used to verify the type of cable connected to a serial interface? |
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Definition
| show controllers serial x/x |
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Term
| What are the commands to troubleshoot PAP/CHAP authentication? |
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Definition
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Term
What does DCE stand for?
What does it do?
What are common examples? |
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Definition
Data circuit-terminating equipment
Receives/converts the signal, provides the clock rate.
Eg. modem, CSU/DSU |
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Term
What does DTE stand for?
What does it do?
What are common examples? |
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Definition
Data terminal equipment
Converts user info to signals.
Eg. PCs, routers, switches |
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