1© 2005 Cisco Systems, Inc. All rights reserved. 111© 2004, Cisco Systems, Inc. All rights reserved.
CNIT 221 Security 1 ver.2Module 8
City College of San FranciscoSpring 2007
2© 2005 Cisco Systems, Inc. All rights reserved.
Network Security 1
Module 8 – Configure Filtering on a Router
3© 2005 Cisco Systems, Inc. All rights reserved.
Learning Objectives
• 8.1 Filtering Technologies
• 8.2 Cisco IOS Firewall Context-Based Access Control
• 8.3 Configure Cisco IOS Firewall Context-Based Access Control
4© 2005 Cisco Systems, Inc. All rights reserved.
Module 8 – Configure Filtering on a Router
8.2 Cisco IOS Firewall Context-Based Access Control
5© 2005 Cisco Systems, Inc. All rights reserved.
Cisco IOS Firewall CBAC
– Packets are inspected upon entering the firewall by CBAC if they are not specifically denied by an ACL.
– CBAC permits or denies specified TCP and UDP traffic through a firewall.
– A state table is maintained with session information.
– ACLs are dynamically created or deleted.
TCP
UDPInternet
6© 2005 Cisco Systems, Inc. All rights reserved.
Cisco IOS ACLs
• Provide traffic filtering by:
– Source and destination IP addresses
– Source and destination ports
• Can be used to implement a filtering firewall
– Ports are opened permanently to allow traffic, creating a security vulnerability.
– Do not work with applications that negotiate ports dynamically.
7© 2005 Cisco Systems, Inc. All rights reserved.
How CBAC Works
8© 2005 Cisco Systems, Inc. All rights reserved.
How CBAC Works (Cont)
9© 2005 Cisco Systems, Inc. All rights reserved.
CBAC Supported Protocols
– TCP (single channel)
– UDP (single channel)
– RPC
– FTP
– TFTP
– UNIX R-commands (such as rlogin, rexec, and rsh)
– SMTP
– HTTP (Java blocking)
– Java
– SQL*Net
– RTSP (such as RealNetworks)
– H.323 (such as NetMeeting, ProShare, CUSeeMe)
– Other multimedia
Microsoft NetShow
StreamWorks
VDOLive
10© 2005 Cisco Systems, Inc. All rights reserved.
Alerts and Audit Trails
• CBAC generates real-time alerts and audit trails.
• Audit trail features use Syslog to track all network transactions.
• With CBAC inspection rules, you can configure alerts and audit trail information on a per-application protocol basis.
11© 2005 Cisco Systems, Inc. All rights reserved.
Access Control List (ACL) Review
12© 2005 Cisco Systems, Inc. All rights reserved.
Identifying Access Lists
• Access list number (All IOS versions)—The number of the access list determines what protocol it is filtering:
– (1-99) and (1300-1399)—Standard IP access lists.
– (100-199) and (2000-2699)—Extended IP access lists.
– (800-899)—Standard IPX access lists.
• Access list name (IOS versions > 11.2)—You provide the name of the access list:
– Names contain alphanumeric characters.
– Names cannot contain spaces or punctuation and must begin with a alphabetic character.
Cisco routers can identify access lists using two methods:
13© 2005 Cisco Systems, Inc. All rights reserved.
Basic Types of IP Access Lists
• Standard—Filter IP packets based on the source address only.
• Extended—Filter IP packets based on several attributes, including:
– Protocol type.
– Source and destination IP addresses.
– Source and destination TCP/UDP ports.
– ICMP and IGMP message types.
Cisco routers support two basic types of IP access lists:
14© 2005 Cisco Systems, Inc. All rights reserved.
Standard Numbered Access List Format
Austin2(config)# access-list 2 permit 36.48.0.3Austin2(config)# access-list 2 deny 36.48.0.0 0.0.255.255Austin2(config)# access-list 2 permit 36.0.0.0 0.255.255.255Austin2(config)# interface e0/1Austin2(config-if)# ip access-group 2 in
Router(config)#
access-list access-list-number {deny | permit} source [source-wildcard]
15© 2005 Cisco Systems, Inc. All rights reserved.
Standard Named Access List Format
Austin2(config)# ip access-list standard protect Austin2(config-std-nacl)# deny 36.48.0.0 0.0.255.255Austin2(config-std-nacl)# permit 36.0.0.0 0.255.255.255Austin2(config)# exit
Router(config)#
ip access-list standard access-list-name
Router(config-std-nacl)#
{deny | permit} source [source-wildcard]
16© 2005 Cisco Systems, Inc. All rights reserved.
Extended Numbered Access List Format
Miami(config)# access-list 103 permit tcp any 128.88.0.0 0.0.255.255 establishedMiami(config)# access-list 103 permit tcp any host
128.88.1.2 eq smtpMiami(config)# interface e0/0Miami(config-if)# ip access-group 103 in
Router(config)#
access-list access-list-number {deny | permit} {protocol-number | protocol-keyword}{source source-wildcard | any | host} {source-port} {destination destination-wildcard | any | host} {destination-port} [established][log | log-input]
Internet
Miami
e0/0
128.88.1.2
128.88.1.0
128.88.3.0
SMTPhost
17© 2005 Cisco Systems, Inc. All rights reserved.
Extended Named Access List Format
Miami(config)# ip access-list extended mailblock Miami(config-ext-nacl)# permit tcp any 128.88.0.0 0.0.255.255 established Miami(config-ext-nacl)# permit tcp any host 128.88.1.2 eq smtpMiami(config-ext-nacl)# exit
Router(config)#
ip access-list extended access-list-name
Router(config-ext-nacl)#
{deny | permit} {protocol-number | protocol-keyword} {source source-wildcard | any | host} {source-port} {destination destination-wildcard | any | host} {destination-port} [established][log | log-input]
18© 2005 Cisco Systems, Inc. All rights reserved.
Commenting IP Access-List Entries
Miami(config)# access-list 102 remark Allow traffic to file serverMiami(config)# access-list 102 permit ip any host 128.88.1.6
Router(config)#
remark message
19© 2005 Cisco Systems, Inc. All rights reserved.
Basic Rules for Developing Access Lists
• Rule #1—Write it out! – Just use Notepad
– Get a piece of paper and write out what you want this access list to accomplish.
– This is the time to think about potential problems.
• Rule #2—Setup a development system.
– Allows you to copy and paste statements easily.
– Allows you to develop a library of access lists.
– Store the files as ASCII text files.
• Rule #3—Apply access list to a router and test.
– If at all possible, run your access lists in a test environment before placing them into production.
Here are some basic rules you should follow when developing access lists:
20© 2005 Cisco Systems, Inc. All rights reserved.
Access List Directional Filtering
Austin1s0/0 e0/0
e0/1
Internet
Inbound Outbound
• Inbound—Data flows toward router interface.
• Outbound—Data flows away from router interface.
21© 2005 Cisco Systems, Inc. All rights reserved.
Applying Access Lists to Interfaces
Tulsa(config)# interface e0/1Tulsa(config-if)# ip access-group 2 in Tulsa(config-if)# exitTulsa(config)# interface e0/2Tulsa(config-if)# ip access-group mailblock out
Router(config)#
ip access-group {access-list-number | access-list-name} {in | out}
22© 2005 Cisco Systems, Inc. All rights reserved.
Displaying Access Lists
Miami# show access-lists
Extended IP access list 102 10 permit ip any host 128.88.1.6
Extended IP access list mailblock 10 permit tcp any 128.88.0.0 0.0.255.255 established
Miami#
Router#
show access-lists {access-list-number | access-list-name}
23© 2005 Cisco Systems, Inc. All rights reserved.
Module 8 – Configure Filtering on a Router
8.3 Configure Cisco IOS Firewall Context-Based Access Control
24© 2005 Cisco Systems, Inc. All rights reserved.
CBAC Configuration
–Pick an Interface – Internal or External.
–Configure IP Access Lists at the interface
–Set audit trails and alerts.
–Set global timeouts and thresholds.
–Define PAM.
–Define inspection rules.
–Apply inspection rules and ACLs to interfaces.
–Test and verify.
25© 2005 Cisco Systems, Inc. All rights reserved.
Enable Audit Trails and Alerts
Router(config)# logging onRouter(config)# logging 10.0.0.3Router(config)# ip inspect audit-trailRouter(config)# no ip inspect alert-off
• Enables the delivery of audit trail messages using Syslog
ip inspect audit-trail
Router(config)#
• Enables real-time alerts
no ip inspect alert-off
Router(config)#
26© 2005 Cisco Systems, Inc. All rights reserved.
ip inspect max-incomplete high number
ip inspect max-incomplete low number
• Defines the number of existing half-opened sessions that cause the software to start deleting half-opened sessions (aggressive mode)
• Defines the number of existing half-opened sessions that cause the software to stop deleting half-opened sessions
Global Half-Opened Connection Limits
Router(config)#
Router(config)#
27© 2005 Cisco Systems, Inc. All rights reserved.
ip inspect one-minute high number
ip inspect one-minute low number
• Defines the number of new half-opened sessions per minute at which they start being deleted
• Defines the number of new half-opened sessions per minute at which they stop being deleted
Router(config)#
Router(config)#
Global Half-Opened Connection Limits
28© 2005 Cisco Systems, Inc. All rights reserved.
Port-to-Application Mapping Overview
• Ability to configure any port number for an application protocol.
• CBAC uses PAM to determine the application configured for a port.
29© 2005 Cisco Systems, Inc. All rights reserved.
ip port-map appl_name port port_num
Router(config)#ip port-map http port tcp 8080
• Maps a port number to an application.
access-list permit acl_num ip_addr
ip port-map appl_name port port_num list acl_num
Router(config)#ip port-map http port tcp 8000 list 99Router(config)#access-list 99 permit host 192.168.1.11
• Maps a port number to an application for a given host.access-list permit acl_num ip_addr wildcard_mask
ip port-map appl_name port port_num list acl_num
• Maps a port number to an application for a given network.
User-Defined Port Mapping – port forwarding
Router(config)#
Router(config)#
Router(config)#
30© 2005 Cisco Systems, Inc. All rights reserved.
show ip port-map • Shows all port mapping information.
show ip port-map appl_name• Shows port mapping information for a given application.
show ip port-map port port_num• Shows port mapping information for a given application on a
given port.
Display PAM Configuration
Router#
Router#
Router#
Router# sh ip port-map ftpDefault mapping: ftp port 21 system definedHost specific: ftp port 1000 in list 10 user
31© 2005 Cisco Systems, Inc. All rights reserved.
ip inspect name inspection-name protocol [alert {on|off}] [audit-trail {on|off}] [timeout seconds]
Inspection Rules for Application Protocols
–Defines the application protocols to inspect.
–Will be applied to an interface
Available protocols: tcp, udp, cuseeme, ftp, http, h323, netshow, rcmd, realaudio, rpc, smtp, sqlnet, streamworks, tftp, and vdolive.
alert, audit-trail, and timeout are configurable per protocol and override global settings.
Router(config)#
Router(config)# ip inspect name FWRULE smtp alert on audit-trail on timeout 300
Router(config)# ip inspect name FWRULE ftp alert on audit-trail on timeout 300
32© 2005 Cisco Systems, Inc. All rights reserved.
Router(config)# ip inspect name FWRULE http java-list 10 alert on audit-trail on timeout 300
Router(config)# ip access-list 10 deny 172.26.26.0 0.0.0.255
Router(config)# ip access-list 10 permit 172.27.27.0 0.0.0.255
• Controls java blocking with a standard ACL.
Inspection Rules for Java
ip inspect name inspection-name http java-list acl-num [alert {on|off}] [audit-trail {on|off}] [timeout seconds]
Router(config)#
33© 2005 Cisco Systems, Inc. All rights reserved.
Router(config)# ip inspect name FWRULE rpc program-number 100022 wait-time 0 alert off audit-trail on
• Allows given RPC program numbers—wait-time keeps the connection open for a specified number of minutes.
Inspection Rules for RPC Applications
ip inspect name inspection-name rpcprogram-number number [wait-time minutes] [alert {on|off}] [audit-trail {on|off}] [timeout seconds]
Router(config)#
34© 2005 Cisco Systems, Inc. All rights reserved.
Router(config)# ip inspect name FWRULE smtp
• Allows only the following legal commands in SMTP applications: DATA, EXPN, HELO, HELP, MAIL, NOOP, QUIT, RCPT, RSET, SAML, SEND, SOML, and VRFY.
• If disabled, all SMTP commands are allowed through the firewall, and potential mail server vulnerabilities are exposed.
Inspection Rules for SMTP Applications
ip inspect name inspection-name smtp [alert {on|off}] [audit-trail {on|off}] [timeout seconds]
Router(config)#
35© 2005 Cisco Systems, Inc. All rights reserved.
Router(config)# ip inspect name FWRULE fragment max 254 timeout 4
• Protects hosts from certain DoS attacks involving fragmented IP packets
– max—number of unassembled fragmented IP packets.
– timeout—seconds when the unassembled fragmented IP packets begin to be discarded.
Inspection Rules for IP Packet Fragmentation
ip inspect name inspection-name fragment max number timeout seconds
Router(config)#
36© 2005 Cisco Systems, Inc. All rights reserved.
ip inspect inspection-name {in | out}
Applying Inspection Rules and ACLs
–Applies the named inspection rule to an interface.
Router (config-if)#
Router(config)# interface e0/0Router(config-if)# ip inspect FWRULE in
• Applies the inspection rule to interface e0/0 in inward direction.
37© 2005 Cisco Systems, Inc. All rights reserved.
General Rules for Applying Inspection Rules and ACLs
• Interface where traffic initiates– Apply ACL on the inward direction that permits only
wanted traffic.
– Apply rule on the inward direction that inspects wanted traffic.
• All other interfaces– Apply ACL on the inward direction that denies all
unwanted traffic.
38© 2005 Cisco Systems, Inc. All rights reserved.
Example—Two Interface Firewall
39© 2005 Cisco Systems, Inc. All rights reserved.
• Apply an ACL and inspection rule to the inside interface in an inward direction.
• Permit inside-initiated traffic from the 10.0.0.0 network.
Router(config)# interface e0/0Router(config-if)# ip inspect OUTBOUND inRouter(config-if)# ip access-group 101 in
Router(config)# access-list 101 permit ip 10.0.0.0 0.0.0.255 any
Router(config)# access-list 101 deny ip any any
Router(config)# ip inspect name OUTBOUND tcpRouter(config)# ip inspect name OUTBOUND udp
• Configure CBAC to inspect TCP and UDP traffic.
Outbound Traffic
40© 2005 Cisco Systems, Inc. All rights reserved.
Router(config)# interface e0/1Router(config-if)# ip access-group 102 in
Router(config)# access-list 102 permit icmp any host 10.0.0.3
Router(config)# access-list 102 permit tcp any host 10.0.0.3 eq www
Router(config)# access-list 102 deny ip any any
• Apply an ACL and inspection rule to outside interface in inward direction.
• Permit outside-initiated ICMP and HTTP traffic to host 10.0.0.3.
Inbound Traffic
41© 2005 Cisco Systems, Inc. All rights reserved.
Example—Three-Interface Firewall
42© 2005 Cisco Systems, Inc. All rights reserved.
• Apply an ACL and inspection rule to the inside interface in an inward direction.
• Permit inside-initiated traffic from 10.0.0.0 network.
Router(config)# interface e0/0Router(config-if)# ip inspect OUTBOUND inRouter(config-if)# ip access-group 101 in
Router(config)# access-list 101 permit ip 10.0.0.0 0.0.0.255 any
Router(config)# access-list 101 deny ip any any
Router(config)# ip inspect name OUTBOUND tcpRouter(config)# ip inspect name OUTBOUND udp
• Configure CBAC to inspect TCP and UDP traffic.
Outbound Traffic
43© 2005 Cisco Systems, Inc. All rights reserved.
• Apply an ACL and inspection rule to the outside interface in an inward direction.
• Permit outside-initiated ICMP and HTTP traffic to host 172.16.0.2.
Router(config)# interface e0/1Router(config-if)# ip access-group 102 in
Router(config)# access-list 102 permit icmp any host 172.16.0.2
Router(config)# access-list 102 permit tcp any host 172.16.0.2 eq www
Router(config)# access-list 102 deny ip any any
Inbound Traffic
Router(config)# ip inspect name INBOUND tcp
• Configure CBAC to inspect TCP traffic.
44© 2005 Cisco Systems, Inc. All rights reserved.
Router(config)# interface e1/0Router(config-if)# ip access-group 103 inRouter(config-if)# ip access-group 104 out
Router(config)# access-list 103 permit icmp host 172.16.0.2 anyRouter(config)# access-list 103 deny ip any any
Router(config)# access-list 104 permit icmp any host 172.16.0.2Router(config)# access-list 104 permit tcp any host 172.16.0.2 eq www
Router(config)# access-list 104 deny ip any any
• Permit only ICMP traffic initiated in the DMZ.
• Permit only outward ICMP and HTTP traffic to host 172.16.0.2.
DMZ-Bound Traffic
• Apply proper access lists and an inspection rule to the interface.
45© 2005 Cisco Systems, Inc. All rights reserved.
show ip inspect name inspection-nameshow ip inspect configshow ip inspect interfacesshow ip inspect session [detail]show ip inspect all
• Displays CBAC configurations, interface configurations, and sessions.
show Commands
Router#
Router# sh ip inspect sessionEstablished Sessions Session 6155930C (10.0.0.3:35009)=>(172.30.0.50:34233) tcp SIS_OPEN
Session 6156F0CC (10.0.0.3:35011)=>(172.30.0.50:34234) tcp SIS_OPEN
Session 6156AF74 (10.0.0.3:35010)=>(172.30.0.50:5002) tcp SIS_OPEN
46© 2005 Cisco Systems, Inc. All rights reserved.
debug ip inspect function-tracedebug ip inspect object-creationdebug ip inspect object-deletiondebug ip inspect eventsdebug ip inspect timers
• General debug commands.
debug Commands
Router#
debug ip inspect protocol• Protocol-specific debug.
Router(config)#
47© 2005 Cisco Systems, Inc. All rights reserved.
no ip inspect
• Removes entire CBAC configuration.
• Resets all global timeouts and thresholds to the defaults.
• Deletes all existing sessions.
• Removes all associated dynamic ACLs.
Remove CBAC Configuration
Router(config)#
48© 2005 Cisco Systems, Inc. All rights reserved.
Firewall and ACL Main Window
49© 2005 Cisco Systems, Inc. All rights reserved. 494949© 2005, Cisco Systems, Inc. All rights reserved.