Demonstrate the use of Network
Address Translation through the use of overloading address
translation.
Equipment Requirements:
Two routers One switch Two
workstations
Background:
A small company has been using the
private address 10.10.10.0/24 for their network. Until recently they
did not need access outside of their own network. Since they now
need Internet access they have been issued the class C address
202.206.154.0 by ARIN. Currently the company needs more than the
number of addresses in a Class C network. For a variety of reasons
including security reasons, the company wishes to hide the internal
network from the outside. All of the users need to be able to
connect to the outside. These users need to have unlimited access to
the outside.
Preliminary:
Before programming the routers, make
sure that the IOS version on the router supports Network address
translation. Load a new IOS version if necessary. Construct the
above network section, using IGRP or RIP as your routing protocol.
Do not advertise the private network. Use the network address
200.200.200.16/28 on the serial link from the stub network router
(Router-B) and the Internet/Network router (Router-A).
The router IP configurations are as
follows:
Router-A
Router-B
Fa
0/0=10.10.10.1/24
S0/0=200.200.200.17/28
S0/0=200.200.200.18/28
Note: actual interfaces used might
vary depending on what type of router used.
When construction of the network is
complete, verify that routers can communicate and are sharing their
routing tables for network 200.200.200.16/28. Also verify that the
workstations are configured correctly for the network in which they
reside. For verification use the show
ip route command, show
interfaces command, show
running-configuration
command, ping,
telnet, and any other
relevant command(s).
For this Lab we will be using
Router-B as the stub network router where we will configure the
network address translation. The router will be translating the
inside local addresses to inside global addresses, in other words,
converting the internal fake addresses into real addresses for use
on the Internet.
From the "Router-B"
console:
Step
1
Enter the EXEC mode.
Step
2
Enter the configuration mode by
entering configure
terminal command at the
router prompt.
Step
3
Define a pool of global addresses to
be allocated as needed.
Enter
ip nat pool net-11 202.206.154.2 202.206.154.17 netmask
255.255.255.0
Step
4
Define a standard access list.
Enter access-list
3 permit 10.10.10.0 0.0.0.255
What is the purpose of the access
list?
Step
5
Establish dynamic source translation,
identifying the access list defined in the prior step.
Enter ip
nat inside source list 3 pool net-11 overload
What does the word
"overload" at the end of the command mean?
Step
6
Specify the inside interface.
Enter
interface fa 0/0 (or
correct inside interface for router used)
Step 7
Mark the interface as connected to
the inside.
Enter
ip nat inside
Step
8
Specify the outside interface.
Enter interface
serial 1 (or correct
outside interface for router used)
Step
9
Mark the interface as connected to
the outside.
Enter
ip nat outside
Step
10
Save configuration information.
Enter CTRL-Z
Enter copy
run start
Step
11
Configure timeout values if required.
Enter
ip nat translation udp-timeout 120
Enter
ip nat translation dns-timeout 60
Enter
ip nat translation tcp-timeout 120
Name a reason when you might want
to give more time than the Cisco default timeout.
Step
12
Monitoring NAT
Enter show
ip nat translations
What information did the router
respond with?
Enter show
ip nat translations verbose
What additional information did the
router respond with?
Enter show
ip nat statistics
What information did the router
respond with?
Did you remember to add the static
route on router A?
From a workstation on the inside
network ping an address on the outside
From the router console
Enter show
ip nat translations
What information did the router
respond with?
Enter show
ip nat statistics
What information did the router
respond with?
From Router-A ping an address
which has a nat listing on the translations table.
Were you successful?
Now from Router-A ping an address
that is not currently in the routers translation table.
Were you successful?
Explain the results of the previous
questions.
What is meant by NAT
"overloading"?
When configuring for overloading
what is the maximum number of translations that can be made with
one inside global IP address?