Use
the terminology from the semester 4 online chapters on WANs.
Experiment
with some WAN related IOS commands
Background:
LANs vs. WANs:
This lab is an introduction to Wide Area Networks (WANs) and the part
routers play in them. Local Area Networks (LANs) typically consist of
a group of computers that are interconnected with hubs or switches
using physical cable (twisted pair copper and multimode fiber). WANs
are made up of two or more LANs that are geographically separate
sites. They typically use services provided by a long distance carrier
with transmission over Fiber or Microwave to connect the sites. An
organization can own the equipment that interconnects its WAN sites
but most often leases WAN links from a service provider.
Routers and WANs:
Although routers can be used to subdivide campus LANs to limit the
size of broadcast domains and help maintain security, they are most
commonly used to interconnect LANs to make WANs. The router is the
interface or gateway from the LAN to the WAN. With most organization's
WANs, each location will have at least one router with an interface or
link to one or more other locations in the WAN. This is usually done
through a CSU/DSU (Channel Service Unit / Data Service Unit). Even
small organizations with a single location today need a router to
connect them to the largest WAN in the world, the Internet.
WANs and the OSI Model:
WAN links typically operate at OSI Layer 2 (Data Link) and convert the
LAN frame encapsulation such as Ethernet or Token Ring to a wide area
Layer 2 frame encapsulation such as HDLC, PPP or Frame Relay. As an
example, let's say you have two Ethernet LANs interconnected by a WAN
link (such as a T1) and a workstation in LAN A needs to connect to a
server in LAN B. The workstation sends a packet to the Ethernet
interface (e.g. E0) of the router in LAN A. That router removes the
Ethernet LAN frame header, replaces it with a WAN frame header such as
Frame Relay or PPP and sends it out one of its serial interfaces (e.g.
S0). When the router on LAN B receives the packet on its serial
interface, it strips off the WAN frame header and replaces it with the
LAN Ethernet frame header. The packet is delivered to the local server
on LAN B through the router's Ethernet interface.
Tools /
Preparation:
Prior to starting the lab, the
teacher or lab assistant should have the standard router lab with
all 5 routers set up. Before beginning this lab you should read the
Networking Academy Second Year Companion Guide, Chapters 8 and 9 on
WANs and WAN Design. You should also review Semester 4 On-line
chapters WANs and WAN Design. Work individually or in teams. The
following is a list of resources required.
Standard Cisco 5-router lab setup
with hubs and switches
Workstation connected to the
router's console port
Step 1 – Review
router lab WAN physical connections
The standard 5-router lab setup uses
WAN serial cables to simulate three wide area network connections
between four of the routers (A,B,C and D). These four routers could
all belong to corporation XYZ and could be located in different
cities across the United States (e.g. Lab-A = Anaheim, CA., Lab-B =
Boise, ID, Lab-C = Chicago, IL., Lab-D = Dallas, TX.). Routers D and
E are attached to a common Ethernet LAN. Normally the cable from the
router in each location would connect to a CSU/DSU (Channel Service
Unit / Data Service Unit) and then to a WAN link such as a T1
(1.544Mbps) from a service provider. With some routers, the CSU is
built-in or can be installed in a modular slot.
One end of each cable is a DB60
(60-pin) connector that attaches to a synchronous serial interface
on the router (S0 or S1 in most cases). The other end is a V.35
connector that normally attaches to the CSU/DSU. The CSU/DSU then
connects to the digital data line (such as a 56K or T1 link) via a
NIU (Network Interface Unit) at the Demarc (demarcation point). This
is the separation point between CPE (Customer Premises Equipment)
and the WAN link service provider's connection. The standard
5-router lab setup simulates the CSU/DSUs on Point-to-Point WAN
links by crossing the connections between the V.35 cables which
eliminates the need for the CSU/DSUs.
The Router is typically the DTE
(Data-circuit Terminating Equipment) and the CSU/DSU is normally the
DCE (Data Communication Equipment). Since there is no CSU/DSU, one
of the routers on each simulated WAN link must play the role of the
DCE in order to provide the synchronous clocking signal. With the
standard lab setup, router Lab-A Serial interface 0 is the DCE and
the clock rate is set to 56000 bps on that interface, simulating a
56K digital data circuit. You must attach the DCE (female) cable to
this router interface. The DTE (male) serial cable is attached to
the Serial 1 interface on the next router Lab-B. No clock is set on
the Lab-B S1 interface. Serial interface S0 on router Lab-B then
becomes the DCE for the next router.
Step 2 - Identify
the router lab WAN connections
Use the standard lab diagram to
identify the Wide Area Network (WAN) links. Fill in the table below
with WAN information contained in the diagram including the number
of the WAN IP network between each pair of routers, the router names
that have WANs between them, the interfaces in use on each router
and the characteristics of the WAN interface cable.
Fill in the following WAN connection
table
WAN IP Network
number
Connects FROM
Which Router and Interface
DCE or DTE?
Connects TO Which
Router and Interface
DCE or DTE?
Step 3 - Diagram the
lab WAN connections
Use the standard lab diagram as a
starting point and draw the physical and logical WAN topology of the
existing lab setup. The main purpose is to identify the routers and
Wide Area Network (WAN) links. Identify and label all WAN connections
(i.e., identify DCE and DTE cables and clock rate etc.
Diagram the WAN links and their
characteristics in the standard lab setup
Step 4 - Review WAN
Connection Options
Refer to the Cisco on-line documentation
and the hardware manuals such as the Cisco 2500 Installation and
Configuration Guide for the routers you are working with.
What are common options or types of
Router WAN connections? (Hint: See question 4)
What Router features and/or additional
hardware would you need to use ISDN, PPP, Frame-Relay or Dial-up WAN
Connections?
Step 5 - Review WAN encapsulation types
The frame encapsulation used at the Data
Link Layer (OSI Layer 2) will vary depending on the WAN technology used
between networks connected by routers. The Data Link encapsulation places
a header and trailer on the packet. Layer 2 framing on a LAN is different
than a WAN and the router must convert between the two.
Check the WAN encapsulation on Lab-A serial
interface 0 using the following command:
Router# show interface s0
What is the default WAN encapsulation
currently in use on the interface between Routers Lab-A and Lab-B?
To see what WAN encapsulation options are
available, us the following commands:
Router(config)# interface Serial 0
Router(config-if) #encapsulation ?
What are some of the Data Link layer WAN
encapsulation types available?
Step 6 - Using WAN Related Router Commands
The following router show commands can help to explore the WAN capabilities
of the router. On a router with standard configurations, try the following
show commands from the privileged EXEC mode, note the results, and answer
the questions.
Show interfaces
What does this command tell you about WAN connections?
Show int s0, show int s1, show int bri0,
show int e0, show int e1 etc.
What do these commands tell you about WAN connections?
Show protocols
What does this command tell you about WAN connections?
Show ip route
What does this command tell you about WAN connections?
Show cdp neighbors
What does this command tell you about WAN connections?
Step 7 - Exploring WAN protocol commands
Try some of these additional WAN protocol related commands. Be sure use a
space and a ? at the end of the command to see the options available. If the
WAN option is not available you will not get an error but no information
will be displayed. Write down some of the options that are displayed.