Sybex CCNA 640-802

Chapter 10: Security

Instructor

& 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

• A PPLICATION LAYER ATTACKS • A UTOROOTERS • B ACKDOORS • D ENIAL OF SERVICE (D O S) AND DISTRIBUTED DENIAL OF SERVICE (DD O S) ATTACKS – ( MANY OTHERS )

Mitigating Attacks

• Appliances – IDS – IPS • S TATEFUL IOS F IREWALL INSPECTION ENGINE • F IREWALL VOICE TRAVERSAL • ICMP INSPECTION • A UTHENTICATION 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, per protocol, • End ACLs with a

permit any

command or per direction • More specific tests at the top of the ACL • Create ACLs & then apply them to an interface • New lists are placed at • ACLs do not filter traffic the bottom of the ACL originated from the • Individual lines cannot be removed router • Put

Standard

ACLs close to the destination • Put

Extended

ACLs close the 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

Standard ACL Example

Standard ACL example 2

Standard ACL Example 3

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

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 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

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 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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