Sybex CCNA 640-802
Chapter 12: Security
Instructor & Todd Lammle
Chapter 1 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
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Introduction to Security
Attacks
•
•
•
•
APPLICATION-LAYER ATTACKS
AUTOROOTERS
BACKDOORS
DENIAL OF SERVICE (DOS)
AND DISTRIBUTED DENIAL OF
SERVICE (DDOS) ATTACKS
– (MANY OTHERS)
Mitigating Attacks
• Appliances
– IDS
– IPS
• STATEFUL IOS FIREWALL
INSPECTION ENGINE
• FIREWALL VOICE TRAVERSAL
• ICMP INSPECTION
• AUTHENTICATION PROXY
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
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
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.
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
ACL Guidelines
• One access list per interface, perprotocol, 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 source
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
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
Wildcards
• What are they???
– Used with access lists to specify
a….
• Host
• Network
• Part of a network
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
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
Standard ACL Example
Standard ACL example 2
Standard ACL Example 3
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
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)
Extended IP Access Lists
• Allows you to choose...
•
•
•
•
IP Source Address
IP Destination Address
Protocol
Port number
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
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
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
Steps (cont.)
RouterA(config)#access-list 110
host 172.16.30.2 eq 23 log
RouterA(config)#access-list 110
0.0.0.0 255.255.255.255
RouterA(config)#ip access-group
or
RouterA(config)#ip access-group
deny tcp any
permit ip any
110 in
110 out
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
Turning Off and Configuring
Network Services
SNMP
Lab_B(config)#access-list 110 deny udp any
any eq snmp
Echo
Lab_B(config)#no service tcp-small-servers
Lab_B(config)#no service udp-small-servers
BootP and Auto-Config
Lab_B(config)#no ip boot server
Lab_B(config)#no service config
Examples – more pages 632-635
Cisco’s Auto Secure
R1#auto secure
--- AutoSecure Configuration --*** AutoSecure configuration enhances the security of the router, but it
will not make it absolutely resistant to all security attacks ***
AutoSecure will modify the onfiguration of your device.
All configuration changes will be shown. For a detailed
explanation of how the configuration changes enhance
security and any possible side effects, please refer to Cisco.com
for Autosecure documentation.
At any prompt you may enter ‘?’ for help.
Use ctrl-c to abort this session at any prompt.
Gathering information about the router for AutoSecure
Is this router connected to internet? [no]: yes
Enter the number of interfaces facing the internet [1]: [enter]
Interface IP-Address OK? Method Status Protocol
FastEthernet0/0 10.10.10.1 YES NVRAM up up
Serial0/0 1.1.1.1 YES NVRAM down down
FastEthernet0/1 unassigned YES NVRAM administratively down down
Serial0/1 unassigned YES NVRAM administratively down down
Enter the interface name that is facing the internet: serial0/0
Securing Management plane services...
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
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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