1.
Sybex CCNA 640-802
Chapter 10: Security
Instructor & Todd Lammle

2.
Chapter 10 Objectives
The CCNA Topics Covered in this chapter
include:
• Introduction to Security
– Types of attacks
– Mitigating attacks
• Access-lists
– Standard
– Extended
– Named
– Monitoring Access-lists
2

3.
Introduction to Security

4.
Attacks
• APPLICATION-LAYER ATTACKS
• AUTOROOTERS
• BACKDOORS
• DENIAL OF SERVICE (DOS)
AND DISTRIBUTED DENIAL OF
SERVICE (DDOS) ATTACKS
– (MANY OTHERS)

5.
Mitigating Attacks
• Appliances
– IDS
– IPS
• STATEFUL IOS FIREWALL
INSPECTION ENGINE
• FIREWALL VOICE TRAVERSAL
• ICMP INSPECTION
• AUTHENTICATION PROXY

6.
Access Lists
• Purpose:
– Used to permit or deny packets
moving through the router
– Permit or deny Telnet (VTY) access
to or from a router
– Create dial-on demand (DDR)
interesting traffic that triggers dialing
to a remote location

7.
Important Rules
• Packets are compared to each line of
the assess list in sequential order
• Packets are compared with lines of
the access list only until a match is
made
– Once a match is made & acted upon no
further comparisons take place
• An implicit “deny” is at the end of
each access list
– If no matches have been made, the
packet will be discarded

8.
Types of Access Lists
• Standard Access List
– Filter by source IP addresses only
• Extended Access List
– Filter by Source IP, Destination IP,
Protocol Field, Port Number
• Named Access List
– Functionally the same as standard and
extended access lists.

9.
Application of Access Lists
• Inbound Access Lists
– Packets are processed before being
routed to the outbound interface
• Outbound Access Lists
– Packets are routed to the outbound
interface & then processed through the
access list

10.
ACL Guidelines
• One access list per
interface, per protocol,
or per direction
• More specific tests at
the top of the ACL
• New lists are placed at
the bottom of the ACL
• Individual lines cannot
be removed
• End ACLs with a permit
any command
• Create ACLs & then
apply them to an
interface
• ACLs do not filter traffic
originated from the
router
• Put Standard ACLs
close to the destination
• Put Extended ACLs
close the the source

11.
Standard IP Access Lists
Router#config t
Enter configuration commands, one per line. End
with CNTL/Z.
Router(config)#access-list ?
<1-99> IP standard access list
<100-199> IP extended access list
<1000-1099> IPX SAP access list
<1100-1199> Extended 48-bit MAC address
access list
<1200-1299> IPX summary address access list
<200-299> Protocol type-code access list
<300-399> DECnet access list
<600-699> Appletalk access list
<700-799> 48-bit MAC address access list
<800-899> IPX standard access list
<900-999> IPX extended access list

12.
Standard IP Access Lists
• Creating a standard IP access list:
Router(config)#access-list 10 ?
deny Specify packets to reject
permit Specify packets to forward
• Permit or deny?
Router(config)#access-list 10 deny ?
Hostname or A.B.C.D Address to match
any any source host
host A single host address
• Using the host command
Router(config)#access-list 10 deny host
172.16.30.2

13.
Standard ACL Example

14.
Standard ACL example 2

15.
Standard ACL Example 3

16.
Wildcards
• What are they???
– Used with access lists to specify
a….
• Host
• Network
• Part of a network

17.
Block Sizes
64 32 16 8 4
• Rules:
– When specifying a range of addresses, choose the
closest block size
– Each block size must start at 0
– A ‘0’ in a wildcard means that octet must match
exactly
– A ‘255’ in a wildcard means that octet can be any
value
– The command any is the same thing as writing out
the wildcard: 0.0.0.0 255.255.255.255

18.
Specifying a Range of Subnets
(Remember: specify a range of values in a block
size)
Requirement: Block access in the range from
172.16.8.0 through 172.16.15.0 = block size 8
Network number = 172.16.8.0
Wildcard = 0.0.7.255
**The wildcard is always one number less than the
block size

19.
Controlling VTY (Telnet)
Access
• Why??
– Without an ACL any user can Telnet
into the router via VTY and gain
access
• Controlling access
– Create a standard IP access list
• Permitting only the host/hosts
authorized to Telnet into the router
– Apply the ACL to the VTY line with
the
access-class command

20.
Example
Lab_A(config)#access-list 50 permit 172.16.10.3
Lab_A(config)#line vty 0 4
Lab_A(config-line)#access-class 50 in
(implied deny)

21.
Extended IP Access Lists
• Allows you to choose...
• IP Source Address
• IP Destination Address
• Protocol
• Port number

22.
Extended IP ACLs
Router(config)#access-list ?
<1-99> IP standard access list
<100-199> IP extended access list
<1000-1099> IPX SAP access list
<1100-1199> Extended 48-bit MAC address access list
<1200-1299> IPX summary address access list
<200-299> Protocol type-code access list
<300-399> DECnet access list
<600-699> Appletalk access list
<700-799> 48-bit MAC address access list
<800-899> IPX standard access list
<900-999> IPX extended access list
Router(config)#access-list 110 ?
deny Specify packets to reject
dynamic Specify a DYNAMIC list of PERMITs or DENYs
permit Specify packets to forward

23.
Extended IP ACLs
Router(config)#access-list 110 deny ?
<0-255> An IP protocol number
ahp Authentication Header Protocol
eigrp Cisco's EIGRP routing protocol
esp Encapsulation Security Payload
gre Cisco's GRE tunneling
icmp Internet Control Message Protocol
igmp Internet Gateway Message Protocol
igrp Cisco's IGRP routing protocol
ip Any Internet Protocol
ipinip IP in IP tunneling
nos KA9Q NOS compatible IP over IP tunneling
ospf OSPF routing protocol
pcp Payload Compression Protocol
tcp Transmission Control Protocol
udp User Datagram Protocol
Router(config)#access-list 110 deny tcp ?
A.B.C.D Source address
any Any source host
host A single source host

24.
Extended IP ACL Steps
#1: Select the access list:
RouterA(config)#access-list 110
#2: Decide on deny or permit:
RouterA(config)#access-list 110 deny
#3: Choose the protocol type:
RouterA(config)#access-list 110 deny tcp
#4: Choose source IP address of the host or network:
RouterA(config)#access-list 110 deny tcp any
#5: Choose destination IP address
RouterA(config)#access-list 110 deny tcp any host 172.16.30.2
#6: Choose the type of service, port, & logging
RouterA(config)#access-list 110 deny tcp any host 172.16.30.2 eq
23 log

25.
Steps (cont.)
RouterA(config)#access-list 110 deny tcp any host 172.16.30.2
eq 23 log
RouterA(config)#access-list 110 permit ip any 0.0.0.0
255.255.255.255
RouterA(config)#ip access-group 110 in
or
RouterA(config)#ip access-group 110 out

26.
Named Access Lists
• Another way to create standard and extended access
lists.
• Allows the use of descriptive names to ease network
management.
• Syntax changes:
– Lab_A(config)#ip access-list standard BlockSales
– Lab_A(config-std-nacl)#deny 172.16.40.0 0.0.0.255
– Lab_A(config-std-nacl)#permit any

27.
Monitoring IP Access Lists
• Display all access lists & their parameters
show access-list
• Show only the parameters for the access list 110
show access-list 110
• Shows only the IP access lists configured
show ip access-list
• Shows which interfaces have access lists set
show ip interface
• Shows the access lists & which interfaces have access
lists set
show running-config

28.
Written Labs and Review
Questions
– Open your books and go through all the
written labs and the review questions.
– Review the answers in class.
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