Sybex CCNA 640-802 Chapter 10: SecurityInstructor & Todd Lammle

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

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: Intrusion Detection System– IPS: Intrusion Prevention System

• 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

Two 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. Any packets that are denied won’t be routed because they are discarded before the routing process.

• Outbound Access Lists– Packets are routed to the outbound

interface & then processed through the access list

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 source

Standard IP Access Lists

Router#config tEnter 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 <1300-1999> IP standard access list (expanded range) <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 commandRouter(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 84

• 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 = 172.16.8.0Wildcard = 0.0.7.255

**The wildcard is always one number less than the block size

Standard ACL Example 1:Prevent Sales users accessing Finance

Lab_A(config)#access-list 10 deny SalesLab_A(config)#access-list 10 permit anyLab_A(config)#int elLab_A(config)#ip access-group 10 out

Standard ACL example 2:Prevent Accounting users accessing HR server

Lab_B(config)#access-list 10 deny 192.168.10.128 0.0.0.31Lab_B(config)#access-list 10 permit anyLab_B(config)#int e0Lab_B(config)#ip access-group 10 out

Standard ACL Example 3:Prevent the four LAN users accessing the Internet

R(config)#access-list 10 deny 172.16.88.0 0.0.7.255R(config)#access-list 10 deny 172.16.192.0 0.0.63.255R(config)#access-list 10 deny 172.16.48.0 0.0.15.255R(config)#access-list 10 deny 172.16.128.0 0.0.31.255R(config)#access-list 10 permit anyR(config)#int s0R(config)#ip access-group 10 out

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 ACLsRouter(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 deny tcp any host 172.16.30.2 eq 23 log

RouterA(config)#access-list 110 permit ip any any

RouterA(config)#ip access-group 110 in

or

RouterA(config)#ip access-group 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

Monitoring IP Access Lists

• Display all access lists & their parametersshow access-list

• Show only the parameters for the access list 110

show access-list 110

• Shows only the IP access lists configuredshow ip access-list

• Shows which interfaces have access lists setshow 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.

28