Contents

Introduction

Prerequisites

Requirements

Components Used

Conventions

Configure

Network Diagram

Configurations

Verify

Troubleshoot

Troubleshooting Commands

Related Information

Introduction

This document provides a sample configuration that shows you how to enable the IOS® router to accept dynamic IPsec connections from an PIX Firewall. The remote router performs Network Address Translation (NAT) if private network 10.0.0.x accesses the Internet. Traffic from 10.0.0.x to private network 10.1.0.x behind the PIX is excluded from the NAT process. The PIX Firewall can initiate connections to the router, but the router cannot initiate connections to the PIX.

This configuration uses a Cisco IOS router in order to create dynamic IPsec LAN-to-LAN (L2L) tunnels with a PIX Firewall that receives dynamic IP addresses on their public interface (outside interface). Dynamic Host Configuration Protocol (DHCP) provides a mechanism in order to allocate IP addresses dynamically from the Internet service provider (ISP). This allows IP addresses to be reused when hosts no longer need them.

Refer to PIX 6.x: Dynamic IPsec Between a Statically Addressed PIX Firewall and the Dynamically Addressed IOS Router with NAT Configuration Example for more information on the scenario where the PIX accepts dynamic IPsec connections from the router.

Refer to PIX/ASA 7.x and later: Dynamic IPsec Between a Statically Addressed PIX and a Dynamically Addressed IOS Router with NAT Configuration Example in order to enable the PIX/ASA Security Appliance to accept dynamic IPsec connections from the IOS router.

Refer to PIX/ASA 7.x and later: Dynamic IPsec Between a Statically Addressed IOS Router and a Dynamically Addressed PIX with NAT Configuration Example in order to learn more about the same scenario where the PIX/ASA Security Appliance runs software version 7.x and later.

Prerequisites

Requirements

There are no specific requirements for this document.

Components Used

The information in this document is based on these software and hardware versions:

- Cisco IOS® Software Release 12.4

- Cisco PIX Firewall Software Release 6.3.4

- Cisco Secure PIX Firewall 515E

- Cisco 2811 Router

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, make sure that you understand the potential impact of any command.

Conventions

Refer to Cisco Technical Tips Conventions for more information on document conventions.

Configure

In this section, you are presented with the information to configure the features described in this document.

Note: Use the Command Lookup Tool (registered customers only) to find more information on the commands used in this document.

Network Diagram

This document uses this network setup:

Configurations

This document uses these configurations:

- PIX 515E

- R2 (Cisco 2811 Router)

PIX 515E

PIX Version 6.3(4)

interface ethernet0 100full

interface ethernet1 100full

interface ethernet2 shut

nameif ethernet0 outside security0

nameif ethernet1 inside security100

nameif ethernet2 intf2 security4

enable password 8Ry2YjIyt7RRXU24 encrypted

passwd 2KFQnbNIdI.2KYOU encrypted

hostname PIX515E

fixup protocol dns maximum-length 512

fixup protocol ftp 21

fixup protocol h323 h225 1720

fixup protocol h323 ras 1718-1719

fixup protocol http 80

fixup protocol rsh 514

fixup protocol rtsp 554

fixup protocol sip 5060

fixup protocol sip udp 5060

fixup protocol skinny 2000

fixup protocol smtp 25

fixup protocol sqlnet 1521

fixup protocol tftp 69

names

!--- The access control list (ACL) to avoid NAT on the IPsec packets.

access-list NO-NAT permit ip 10.1.0.0 255.255.255.0 10.0.0.0 255.255.255.0

!--- The ACL to apply on crypto map. !--- Include the private-network-to-private-network traffic !--- in the encryption process.

access-list 101 permit ip 10.1.0.0 255.255.255.0 10.0.0.0 255.255.255.0

pager lines 24

logging on

mtu outside 1500

mtu inside 1500

mtu intf2 1500

!--- ISP will providthe the Outside IP address.

ip address outside dhcp

ip address inside 10.1.0.3 255.255.255.0

ip audit info action alarm

ip audit attack action alarm

no failover

failover timeout 0:00:00

failover poll 15

no failover ip address outside

no failover ip address inside

no failover ip address intf2

pdm history enable

arp timeout 14400

global (outside) 1 interface

nat (inside) 0 access-list NO-NAT

nat (inside) 1 0.0.0.0 0.0.0.0 0 0

route outside 10.0.0.0 255.255.255.0 172.16.1.5 1

timeout xlate 3:00:00

timeout conn 1:00:00 half-closed 0:10:00 udp 0:02:00 rpc 0:10:00 h225 1:00:00

timeout h323 0:05:00 mgcp 0:05:00 sip 0:30:00 sip_media 0:02:00

timeout uauth 0:05:00 absolute

aaa-server TACACS+ protocol tacacs+

aaa-server TACACS+ max-failed-attempts 3

aaa-server TACACS+ deadtime 10

aaa-server RADIUS protocol radius

aaa-server RADIUS max-failed-attempts 3

aaa-server RADIUS deadtime 10

aaa-server LOCAL protocol local

no snmp-server location

no snmp-server contact

snmp-server community public

no snmp-server enable traps

floodguard enable

sysopt connection permit-ipsec

!--- IPsec configuration, Phase 2.

crypto ipsec transform-set DYN-TS esp-des esp-md5-hmac

crypto map IPSEC 10 ipsec-isakmp

crypto map IPSEC 10 match address 101

crypto map IPSEC 10 set peer 10.95.49.1

crypto map IPSEC 10 set transform-set DYN-TS

crypto map IPSEC interface outside

!--- Internet Security Association and Key Management Protocol (ISAKMP) !--- policy, Phase 1. !--- Note: In real show run output, the pre-shared key appears as *******.

isakmp enable outside

isakmp key cisco123 address 10.95.49.1 netmask 255.255.255.255

isakmp policy 10 authentication pre-share

isakmp policy 10 encryption des

isakmp policy 10 hash md5

isakmp policy 10 group 1

isakmp policy 10 lifetime 86400

telnet timeout 5

ssh timeout 5

console timeout 0

terminal width 80

Cryptochecksum:f0294298e214a947fc2e03f173e4a405

: end

R2 (Cisco 2811 Router)

R2#show running-configuration

Building configuration...

Current configuration : 1916 bytes

!

version 12.4

service timestamps debug datetime msec

service timestamps log datetime msec

service password-encryption

!

hostname r1800

!

boot-start-marker

boot-end-marker

!

!

no aaa new-model

!

resource policy

!

mmi polling-interval 60

no mmi auto-configure

no mmi pvc

mmi snmp-timeout 180

ip subnet-zero

ip cef

!

!

no ip dhcp use vrf connected

!

!

no ip ips deny-action ips-interface

!

no ftp-server write-enable

!

!

!--- ISAKMP policy, Phase 1.

crypto isakmp policy 10

hash md5

authentication pre-share

crypto isakmp key 6 cisco123 address 0.0.0.0 0.0.0.0

!

!

!--- IPsec policy, Phase 2.

crypto ipsec transform-set DYN-TS esp-des esp-md5-hmac

!

crypto dynamic-map DYN 10

set transform-set DYN-TS

match address 101

!

!

crypto map IPSEC 10 ipsec-isakmp dynamic DYN

!

!

!

interface FastEthernet0/0

ip address 10.95.49.1 255.255.255.0

ip nat outside

ip virtual-reassembly

load-interval 30

duplex auto

speed auto

crypto map IPSEC

!

interface FastEthernet0/1

ip address 10.0.0.1 255.255.255.0

ip nat inside

ip virtual-reassembly

duplex auto

speed auto

!

ip classless

ip route 10.1.0.0 255.255.255.0 10.95.49.2

!

ip http server

no ip http secure-server

!--- Except the private network from the NAT process.

ip nat inside source list 102 interface FastEthernet0/0 overload

!

!--- Include the private-network-to-private-network !--- traffic in the encryption process.

access-list 101 permit ip 10.0.0.0 0.0.0.255 10.1.0.0 0.0.0.255

!--- Except the private network from the NAT process.

access-list 102 deny ip 10.0.0.0 0.0.0.255 10.1.0.0 0.0.0.255

access-list 102 permit ip 10.0.0.0 0.0.0.255 any

!

!

control-plane

!

!

line con 0

exec-timeout 0 0

line aux 0

line vty 0 4

exec-timeout 0 0

login

!

end

Verify

Use this section to confirm that your configuration works properly.

The Output Interpreter Tool (registered customers only) (OIT) supports certain show commands. Use the OIT to view an analysis of show command output.

- show crypto isakmp sa—Shows all current IKE security associations (SAs) at a peer.

- show crypto ipsec sa—Shows the settings used by current (IPsec) SAs.

- show crypto engine connections active—Shows current connections and information regarding encrypted and decrypted packets (router only).

You must clear SAs on both peers.

Perform these PIX commands in config mode.

- clear crypto isakmp sa—Clears the Phase 1 SAs.

- clear crypto ipsec sa—Clears the Phase 2 SAs.

Perform these router commands in enable mode.

- clear crypto isakmp—Clears the Phase 1 SAs.

- clear crypto sa—Clears the Phase 2 SAs.

Troubleshoot

Use this section to troubleshoot your configuration.

Troubleshooting Commands

The Output Interpreter Tool (registered customers only) (OIT) supports certain show commands. Use the OIT to view an analysis of show command output.

Note: Refer to Important Information on Debug Commands before you use debug commands.

- show crypto isakmp sa—View all current IKE SAs at a peer.

- show crypto ipsec sa—Shows the settings used by current (IPsec) SAs.

- show crypto engine connections active—Shows current connections and information regarding encrypted and decrypted packets (router only).

Related Information

- Most Common L2L and Remote Access IPSec VPN Troubleshooting Solutions

- Cisco PIX Firewall Software

- Cisco Secure PIX Firewall Command References

- Requests for Comments (RFCs)

- IPsec Negotiation/IKE Protocols