Vol 1 Ch 3 - Fundamentals of WANs and IP Routing

Question 1

Leased-Line WAN

Answer 1

Two pairs of wires, sending and receiving.
It acts as a crossover Ethernet link, but the physical reality is hidden from the customer.
Full duplex.
Also known as:
Leased circuit
Serial link, serial line
Point-to-point link, point-to-point line
T1
WAN link, Link
Private line

Question 2

HDLC

Answer 2

High-Level Data Link Control

Has address field but it is unimportant, because it is a point to point connection.

Question 3

HDLC vs Ethernet fields

Answer 3

HDLC Field / Ethernet Field / Description
Flag / Preamble, SFD / Identifies the destination device
Address / Destination Address / destination device
Control / NA / Mostly not in use today
Type / Type / Identifies the layer 3 packet
FCS / FCS / error check, only field in the trailer

Question 4

Type field in HDLC

Answer 4

Only used by Cisco. Not in ISO standard of HDLC.

Question 5

Benefits of leased lines

Answer 5

1. Simple for the customer.
2. Widely available.
3. High quality.
4. Private

Question 6

Negatives of leased lines compared to newer WAN technologies.

Answer 6

1. Higher cost.
2. Longer lead times to install.
3. Slow, by today’s standards.

Question 7

Ethernet WAN IEEE standards

Answer 7

1000BASE-LX - single mode fiber - 5 km

1000BASE-ZX - 70 km

Question 8

Common Ethernet WAN names

Answer 8

1. Ethernet WAN
2. E-Line (Ethernet Line Service)
3. Ethernet emulation
4. Ethernet over MPLS (EoMPLS) - Multiprotocol Label Switching

Question 9

Which network devices build frames?

Answer 9

Hosts and routers are the only devices that build frames to encapsulate IP packets.

Question 10

Which network devices remove frames?

Answer 10

Hosts and routers are the only devices that remove (de-encapsulate) frames if the frame is addressed to them.

Question 11

Are two IP addresses separated by a router in the same network or subnet?

Answer 11

No. The two IP addresses are in different networks (subnets) if they are separated by a router.

Question 12

Are two IP addresses not separated by a router in the same network or subnet?

Answer 12

Yes. The two IP addresses are in the same network (subnet) if they are NOT separated by a router.

Question 13

What are the general steps used by routers to learn routes?

Answer 13

1. Adds a route to its routing table for each directly connected subnet.
2. Tells its neighbors about the route sin its routing table, including directly connected routes and routes learned from other routers.
3. Adds routes learned from neighbors to its routing table, including the next-hop. Add a metric, if there are competing routes.

Question 14

What are three important network layer (layer 3) features?

Answer 14

1. Domain Name Services (DNS)
2. Address Resolution Protocol (ARP)
3. ICMP and the Ping command

Question 15

What does DNS do?

Answer 15

The host sues DNS to resolves host names into matching IP addresses.

Question 16

What does ARP do?

Answer 16

A host uses ARP to dynamically learn the MAC address of another IP host.

Question 17

What does Ping do?

Answer 17

The Ping (Packet Internet Groper) command uses the ICMP (Internet Control Message Protocol) to send an ICMP echo request to another IP address. The host with the IP address should reply with an ICMP echo reply. If that works, you have successfully tested the IP network (there and back). Since ICMP does not rely on any application, it really just tests basic IP connectivity - Layers 1, 2, and 3.