Lab 1.3.4 Creating an ACL

Step 1: Analyze the traffic filtering requirements

a. Determine the access and filtering requirements.

For this lab:

1) PC1 is a network administrator’s workstation. This host must be permitted FTP and HTTP access to the network server, and telnet access to the router FC-CPE-1.

2) PC2 is a general workstation that is to have HTTP access only. FTP services and Telnet access to the router is not permitted.

b. Having determined specific requirements, decide if all other traffic is to be allowed or denied.

List the benefits and potential problems to the following filtering scenarios:

Benefits of allowing all other traffic:

Jawaban :

layanan yang ada untuk ke depannya tidak dihalangi atau diblokir

Potential problems with allowing all other traffic:

Jawaban :

Trafik berbahaya dan tidak diinginkan tidak diblok

Benefits of denying all other traffic:

Jawaban :

Trafik yang berbahaya dan tidak diinginkan diblok secara otomatis

Potential problems with denying all other traffic:

Jawaban :

Layanan yang diimplementasikan ke depannya akan diblok secara otomatis.

Step 2: Design and create the ACL

a. Review, and then apply, ACL recommended practice.

• Always plan thoroughly before implementation.
• The sequence of the statements is important. Put the more specific statements at the beginning and the more general statements at the end.
• Statements are added to the end of the ACL as they are written.
• Create and edit ACLs with a text editor and save the file.
• Use Named ACLs wherever possible.
• Use comments (remark option) within the ACL to document the purpose of the statements.
• To take effect, ACLs must be applied to an interface.
• An interface can have one ACL per Network Layer protocol, per direction.
• Although there is an implicit deny any statement at the end of every ACL, it is good practice to configure this explicitly. This ensures that you remember that the effect is in place and allows logging of matches to this statement to be used.
• ACLs with many statements take longer to process, which may affect router performance.
• Placement of ACLs:

o Standard: closest to destination (if have administrative authority on that router)

o Extended: closest to source (if have administrative authority on that router)

b. Consider the two approaches to writing ACLs:

• Permit specific traffic first and then deny general traffic.
• Deny specific traffic first and then permit general traffic.

When would it be best to permit specific traffic first and then deny general traffic?

Jawaban :

ACL tanpa banyak statement mengurangi paket latency

When would it be best to deny specific traffic first and then permit general traffic?

Jawaban :

When there is likely to be more traffic of the type to be denied – these packets are matched early in the ACL without having to traverse many statements, minimizing router latency.

c. Select one approach and write the ACL statements that will meet the requirements of this lab.

Allow PC1 to access server http and ftp

access-list 101 permit tcp host 10.0.0.10 host 172.17.1.1 eq www log

access-list 101 permit tcp host 10.0.0.10 host 172.17.1.1 eq ftp log

Allow PC2 to access web server

access-list 101 permit tcp host 10.0.0.201 host 172.17.1.1 eq www log

Allow PC1 ftp access to router Fa0/0

access-list 101 permit tcp host 10.0.0.10 host 10.0.0.1 eq telnet log

Deny all other traffic

access-list 101 ip deny any any log

After an ACL is written and applied to an interface, it is useful to know if the ACL statements are having the desired effect. The number of packets that meet the conditions of each ACL statement can be logged by adding the option log at the end of each statement.

Why is it important to know to how many times packets that match an ACL statement are denied?

Jawaban :

This potentially shows the number of attempts at unauthorized access to denied services that may lead to further investigation of network usage.

Step 3: Cable and configure the given network

NOTE: If the PCs used in this lab are also connected to your Academy LAN or to the Internet, ensure that you record the cable connections and TCP/IP settings so these can be restored at the conclusion of the lab.

a. Referring to the topology diagram, connect the console (or rollover) cable to the console port on the router and the other cable end to the host computer with a DB-9 or DB-25 adapter to the COM 1 port.

Ensure that power has been applied to both the host computer and router.

b. Connect and configure the devices in accordance with the given topology and configuration. Your instructor may substitute Discovery Server with an equivalent server for this lab.

c. Establish a HyperTerminal, or other terminal emulation program, from PC1 to Router R1.

d. From the global configuration mode issue the following commands:

Router(config)#hostname FC-CPE-1

FC-CPE-1(config)#interface FastEthernet0/0

FC-CPE-1(config-if)#ip address 10.0.0.1 255.255.255.0

FC-CPE-1(config-if)#no shutdown

FC-CPE-1(config-if)#exit

FC-CPE-1(config)#interface FastEthernet0/1

FC-CPE-1(config-if)#ip address 172.17.0.1 255.255.0.0

FC-CPE-1(config-if)#no shutdown

FC-CPE-1(config-if)#exit

FC-CPE-1(config)#line vty 0 4

FC-CPE-1(config-line)#password telnet

FC-CPE-1(config-line)#login

FC-CPE-1(config-line)#end

e. Ping between PC1 and Discovery Server to confirm network connectivity. Troubleshoot and establish connectivity if the pings fail.

Step 4: Test the network services without ACLs

Perform the following tests on PC1:

a. Open a web browser on PC1 and enter the URL http://172.17.1.1 at the address bar.

What web page was displayed?

Jawaban :

Discovery Server Home Page

b. Open a web browser on PC1 and enter the URL ftp://172.17.1.1 at the address bar.

What web page was displayed?

Jawaban :

Discovery FTP Home Directory

c. On the Discovery FTP Home Directory, open the Discovery 1 folder. Click and drag a Chapter file to the local Desktop. Did the file copy successfully?

Jawaban :

Ya

d. From the PC1 command line prompt, issue the command telnet 10.0.0.1, or use a Telnet client (HyperTerminal or TeraTerm, for example) to establish a Telnet session to the router.

What response did the router display?

Jawaban :

Prompt untuk password Telnet dan login ke router

e. Exit the Telnet session.

Quit

Perform the following tests on PC2:

a. Open a web browser on PC2 and enter the URL http://172.17.1.1 at the address bar.

What web page was displayed?

Jawaban :

Discovery Server Home Page

b. Open a web browser on PC2 and enter the URL ftp://172.17.1.1 at the address bar.

What web page was displayed?

Jawaban :

Discovery FTP Home Directory

c. On the Discovery FTP Home Directory, open the Discovery 1 folder. Click and drag a Chapter file to the local Desktop. Did the file copy successfully?

Jawaban :

Ya

d. From the PC2 command line prompt, issue the command telnet 10.0.0.1, or use a Telnet client (HyperTerminal or TeraTerm, for example) to establish a Telnet session to the router.

What response did the router display?

Jawaban :

Prompt untuk password Telnet dan login ke router

e. Exit the Telnet session.

quit

Why was each of the above connections successful?

Jawaban :

There were no data access or filtering controls in place.

Successful connection was expected.

If any of the above connections was not successful, troubleshoot the network and configurations and establish each type of connection from each host.

Step 5: Configure the network services ACL

From the global configuration mode issue the following commands:

a. Allow PC1 to access the web server and telnet to the router.

FC-CPE-1(config)#ip access-list extended Server-Access

FC-CPE-1(config-ext-nacl)#remark Allow PC1 access to server

FC-CPE-1(config-ext-nacl)#permit tcp host 10.0.0.10 host 172.17.1.1 eq

ftp www log

b. Allow PC2 to access the web server.

FC-CPE-1(config-ext-nacl)#remark Allow PC2 to access web server

FC-CPE-1(config-ext-nacl)#permit tcp host 10.0.0.201 host 172.17.1.1 eq

www log

c. Allow PC1 telnet access to router

FC-CPE-1(config-ext-nacl)#remark Allow PC1 to telnet router

FC-CPE-1(config-ext-nacl)#permit tcp host 10.0.0.10 host 10.0.0.1 eq telnet log

d. Deny all other traffic.

FC-CPE-1(config-ext-nacl)#remark Deny all other traffic

FC-CPE-1(config-ext-nacl)#deny ip any any log

FC-CPE-1(config-ext-nacl)#exit

Step 6: Apply the ACLs

a. Apply the Extended ACL to the router interface closest to the source.

FC-CPE-1(config)#interface FastEthernet0/0

FC-CPE-1(config-if)#ip access-group Server-Access in

FC-CPE-1(config-if)#end

b. From the Privileged EXEC mode, issue the show running-configuration command and

confirm that the ACLs have been configured and applied as required.

Reconfigure if errors are noted.

Step 7: Test the network services with ACLs

Perform the following tests on PC1:

a. Open a web browser on PC1 and enter the URL http://172.17.1.1 at the address bar.

What web page was displayed?

Jawaban :

Discovery Server Home Page

b. Open a web browser on PC1 and enter the URL ftp://172.17.1.1 at the address bar.

What web page was displayed?

Jawaban :

Discovery FTP Home Directory

c. On the Discovery FTP Home Directory, open the Discovery 1 folder. Click and drag a Chapter file to the local Desktop. Did the file copy successfully?

Jawaban :

Ya

Why is this the outcome?

Jawaban :

Host ini memungkinkan akses FTP

d. From the PC1 command line prompt, issue the command telnet 10.0.0.1, or use a Telnet client (HyperTerminal or TeraTerm, for example) to establish a Telnet session to the router.

What response did the router display?

Jawaban :

Prompt untuk password Telnet dan login ke router

Why is this the outcome?

Jawaban :

Host ini memungkinkan akses Telnet

e. Exit the Telnet session.

Perform the following tests on PC2:

a. Open a web browser on PC2 and enter the URL http://172.17.1.1 at the address bar.

What web page was displayed?

Jawaban :

Discovery Server Home Page

Why is this the outcome?

Jawaban :

Host ini memungkinkan akses web

b. Open a web browser on PC2 and enter the URL ftp://172.17.1.1 at the address bar.

What web page was displayed?

Jawaban :

error page cannot be displayed

Why is this the outcome?

Jawaban :

Host ini tidak memungkinkan akses FTP

c. From the PC2 command line prompt, issue the command telnet 10.0.0.1, or use a Telnet client (HyperTerminal or TeraTerm, for example) to establish a Telnet session to the router.

What response did the router display?

Jawaban :

Telnet connection refused.

Why is this the outcome?

Jawaban :

Host tidak memungkinkan akses Telnet

If any of these transactions did not result in the expected outcome, troubleshoot the network and configurations and retest the ACLs from each host.

Step 8: Observe the number of statement matches

a. From the Privileged EXEC mode, issue the command:

FC-CPE-1#show access-list Server-Access

List the number of matches logged against each ACL statement.

Step 9: Clean up

Erase the configurations and reload the routers and switches. Disconnect and store the cabling. For PC hosts that are normally connected to other networks (such as the school LAN or to the Internet), reconnect the appropriate cabling and restore the TCP/IP settings.

Challenge

Rewrite the Server-Access ACL used in this lab so that:

1) Administrator workstations are considered to be in the address range of 10.0.0.10 /24 to

10.0.0.15 /24 instead of a single host; and,

2) The general workstations have the address range of 10.0.0.16 /24 to 10.0.0.254 /24 instead of

being a single host.

Jawaban :

ip access-list extended Server-Access

remark Allow PC1 to access any IP traffic

permit ip host 10.0.0.0 0.0.0.15 172.17.1.1 log

remark Allow PC2 to access web server

permit ip host 10.0.0.0 0.0.0.255 172.17.1.1 eq www log

remark Deny all other traffic

deny ip any any log

Running config of router after lab completion:

FC-CPE-1#show run

Building configuration…

Current configuration : 1309 bytes

!

version 12.4

service timestamps debug datetime msec

service timestamps log datetime msec

no service password-encryption

!

hostname FC-CPE-1

!

boot-start-marker

boot-end-marker

!

!

no aaa new-model

!

resource policy

!

mmi polling-interval 60

no mmi auto-configure

no mmi pvc

mmi snmp-timeout 180

ip subnet-zero

ip cef

!

!

!

!

!

!

!

!

!

interface FastEthernet0/0

ip address 10.0.0.1 255.255.255.0

ip access-group Server-Access in

duplex auto

speed auto

!

interface FastEthernet0/1

ip address 172.17.0.1 255.255.0.0

duplex auto

speed auto

!

interface FastEthernet0/0/0

!

interface FastEthernet0/0/1

!

interface FastEthernet0/0/2

!

interface FastEthernet0/0/3

!

interface Serial0/1/0

no ip address

shutdown

clock rate 125000

!

interface Serial0/1/1

no ip address

shutdown

clock rate 125000

!

interface Vlan1

no ip address

!

ip classless

!

ip http server

!

ip access-list extended Server-Access

remark Allow PC1 access to server

permit tcp host 10.0.0.10 host 172.17.1.1 eq ftp www

remark Allow PC2 to access web server

permit tcp host 10.0.0.201 host 172.17.1.1 eq www

remark Allow PC1 to telnet router

permit tcp host 10.0.0.10 host 10.0.0.1 eq telnet

remark Deny all other traffic

deny ip any any

!

!

control-plane

!

!

line con 0

line aux 0

line vty 0 4

password telnet

login

!

end

FC-CPE-1#