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http://webpages.uncc.edu/~tkombol/Classes_2014_Fall/ITIS2110/2110LabSchedule.htm#wk13
Lab 13
◦ In-lab project work time
 TA available for help
◦ Will take attendance
◦ Quick lecture on project expectations
◦ Status sheet with signatures due by end of lab period
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Lab 14
◦ Project due
◦ Presentations
Brief
overview
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Your network is 152.8.0.0/16.
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Everyone has the same IP address range
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Any address that starts with 152.8 is
considered local.
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A local network
Anything else is “outside”
Rules specify source and destination IP
addresses
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Rules are for many types of interface
2 styles for IP
◦ Basic (in bound only from a source)
◦ Extended (in and out bound)
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We’ll concentrate on the extended IP style
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access-list number
{permit | deny}
[protocol]
{any | ipaddr mask | host ipaddr}
{any | ipaddr mask | host ipaddr}
[operator port | established]
[log]
◦
◦
◦
◦
Bold items are entered verbatim
[…] items are optional
{…} must be entered
| denotes “or”
◦ The command must be all on one line
access-list 111 permit tcp any host 152.8.1.10 eq 80
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access-list
◦ All firewall configuration ACL commands start with this keyword
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number
◦ A number typically between
 E.g. IP is 0-99 or 1300-1999, IPX is 100-199 or 2000-2699
 Think of it as the name of the list
 Number range implies type of protocol involved
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permit or deny
◦ Whether to permit or deny this packet of information if
conditions match
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protocol (optional)
◦ Type of protocol for this packet: IP, ICMP, SNMP, UDP or TCP
 If omitted, then this command pertains to all network traffic
regardless of protocol
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Source Address
◦ Internet address of the sender of the packet
◦ Can be:
 any - This access command applies to packets from any source
 host ipaddr - Command applies to one particular computer
 IP address of the computer
 Dotted decimal format (i.e. 152.8.1.2)
 ipaddr mask – “sub-net” range affected
 IP network address of the packet's source
 Dotted-decimal format
 Followed by a mask (dotted-decimal format)
 When comparing the packet's source address, any address bit whose
mask bit is one is ignored
 152.8.12.47 0.0.255.255
 represents all IP addresses whose first 16 bits match
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Destination Address
◦ Internet address of the network packet's destination
 Specified in the same three formats as the source address
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Operator (optional)
◦ Applies to TCP or UDP ports only
◦ Indicates how the port number in the packet should be
compared
◦ If omitted, command applies for all ports

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
eq
lt
gt
neq
range
equal
less than
greater than
not equal
a range of ports
 Must specify two different port numbers
 est
established connections
 Allows packets to pass through the firewall from the
Internet if they are the response to a connection
established from within the intranet
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Port (optional)
◦ TCP/UDP destination port number
◦ If omitted, command applies for all port numbers
◦ Port number must be specified if an operator is given
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Log (optional)
◦ Whether to log this entry to the console
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Commands are case insensitive
◦ Note: all access-list commands must fit on one line
◦ Comments can be included configuration
 Comments start with an exclamation point ( ! )
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Examples:
◦ access-list 111 permit tcp any host 152.8.1.10 eq 80
 Permits any computer on the Internet to connect to the
computer whose
 IP host address is 152.8.1.1
 uses the TCP protocol
 port 80
◦ access-list 123 deny any 178.22.8.9 0.0.255.255
 This will prohibit any computer from accessing a computer on
the 178.22 domain using any protocol
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When a packet arrives at your firewall
◦ it will be compared with each access-list statement
in the order they appear
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The first statement that applies to that
packet determines if it is permitted or denied
For incoming traffic
◦ Implicit deny everything else at the end of the
access-lists
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For outgoing traffic
◦ Implicit permit everything else at the end of the
access-lists
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IP address format:
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any
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host 152.8.1.10
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matches one IP address
152.8.1.1 0.0.255.255
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matches anything
matches a (sub)network
Note: the Cisco netmask is backwards from what you're used to!
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Called an inverse mask
0's mean "don't care"
access-list 101 deny tcp any 152.8.0.0 0.0.255.255 eq 80
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Block all incoming TCP traffic to port 80
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“any” is the source address
“152.8.0.0 0.0.255.255” is the destination.
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In this case, it refers to any IP address that starts
with 152.8.
This blocks packets from entering your
network from outside
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Protects your internal or rogue Web servers
access-list 101 deny tcp 152.8.0.0 0.0.255.255 any eq 80
Block all outgoing TCP traffic to port 80
 “152.8.0.0 0.0.255.255” is the source
 “any” is the destination.
 block all packets from the local network to
the everything on port 80 outside
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access-list 101 allow tcp any host 152.8.1.10 eq 80
access-list 101 deny tcp any 152.8.0.0 0.0.255.255 eq 80
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Block all incoming port 80 traffic EXCEPT traffic to
our Web server
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152.8.1.10
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152.8.0.0 0.0.255.255
Second rule blocks packets from outside to all inside
A packet going to the Web server
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First rule permits packets to the Web server
Matches the first rule and stops being processed
Packet allowed to go to the Web server
A packet going anywhere else
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Doesn't match the first rule, so it gets caught by the second
rule
It is denied, or blocked
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We don't want employees in a certain subnet
reading Reddit while at work. Block packets
from 152.8.100.0/24 to www.reddit.com
(72.246.25.35)
access-list 101 deny tcp 152.8.100.0 0.0.0.255 host 72.246.25.35
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Note: we're only interested in IP addresses starting with
152.8.100, so the netmask is 0.0.0.255
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The ACLs are for an interface
◦ E.g for a specific Ethernet port (plug)
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For extended IP rules need ACLs:
◦ For the outward facing ports (the internet)
◦ For the internal ones
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Each rule needs source and destination
addresses
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The protocol for a service isn't always TCP
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The number after “access-list” isn't important
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DNS, for example, uses UDP
You can leave out the protocol entirely to operate on
all protocols.
Can use the same number for every rule
Should use a number for the type of rule
Any incoming packets not covered by a rule
are blocked by default
Any outgoing packets not covered by a rule are
allowed by default
Mode
Access Method
Prompt
User Exec
Begin a new session
Router>
Privileged Exec
Enter enable from user Exec
Router#
Global Configuration
Enter configure from privileged Exec
Mode
Enter interface FastEthernet number
from global mode
Router(config)#
Interface Configuration
Router(config-if)#
•These Cisco IOS command modes are hierarchical.
•When you begin a router session, you are in user EXEC mode.
•You can see a list of available commands for a particular mode by entering a question
mark (?) at the prompt.
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When the 850 is reset:
◦ Get a default UID of “cisco” and PW of “cisco”
◦ One time use only!
◦ Must create a new user for use next time
restart/login
 Otherwise will need to reset the router and start all
over again!
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Minicom
◦ Don’t forget to turn line wrap on!
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When first started or reset the Cisco 850
router does absolutely nothing
Must turn on and configure services
◦ Enable NAT
◦ Enable and configure DHCP
◦ Set up ACLs (Access Control Lists)
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This lab will use Minicom to configure the
router through the serial port
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Answer the questions and the items marked **
Work in pairs
When “fresh from the box” or reset:
◦ The router is a brick
 Does nothing
◦ Needs to be configured
 Includes new ID and PW
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Optional:
◦ Turn in copy of lab with comments
 Only if errors or incomplete instructions
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Short paper describing the lab with an
introduction, body and summary
Answer the questions and the **ed items