Configuring a GRE Tunnel over IPsec with OSPF

Introduction

Normal IP Security (IPsec) configurations cannot transfer routing protocols, such as Enhanced Interior Gateway Routing Protocol (EIGRP) and Open Shortest Path First (OSPF), or non-IP traffic, such as Internetwork Packet Exchange (IPX) and AppleTalk. This document illustrates how to route between different networks that use a routing protocol and non-IP traffic with IPsec. This example uses generic routing encapsulation (GRE) in order to accomplish routing between the different networks.

Refer to PIX/ASA 7.x and later : VPN/IPsec with OSPF Configuration Example for more information on how to configure for a VPN/IPsec with Open Shortest Path First (OSPF) without a GRE tunnel on Cisco PIX Security Appliance Software Version 7.x or Cisco Adaptive Security Appliance (ASA).

Refer to Configuring IPsec Router-to-Router Hub and Spoke with Communication Between the Spokes for information on how to configure a hub and spoke IPsec design between three routers.

Refer to Configuring Router-to-Router IPSec (Pre-shared Keys) on GRE Tunnel with IOS Firewall and NAT for information on how to configure the basic Cisco IOS^® Firewall configuration on a GRE tunnel with Network Address Translation (NAT).

Prerequisites

Requirements

Ensure that you meet these requirements before you attempt this configuration:

• Make sure that the tunnel works before you apply the crypto maps.

• Refer to Adjusting IP MTU, TCP MSS, and PMTUD on Windows and Sun Systems for information about possible Maximum Transmission Unit (MTU) issues.

Components Used

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

• Cisco 3600 that runs Cisco IOS Software Release 12.4(8)

• Cisco 2600 that runs Cisco IOS Software Release 12.4(8)

• PIX Firewall (Lion) Software Release 6.3(5)

• PIX Firewall (Tiger) Software Release 6.3(5)

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 used 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:

Note: The IP addressing schemes used in this configuration are not legally routable on the Internet. These are RFC 1918 addresses which have been used in a lab environment.

Note: Crypto does not support the Cisco 7600 Series Router. You may have to install the VPN module in order for this to work.

Configurations

This document uses these configurations:

• PIX Lion

• PIX Tiger

• Router Rodney

• Router House

PIX Version 6.3(5)
interface ethernet0 auto
interface ethernet1 auto
interface ethernet2 auto shutdown
interface ethernet3 auto shutdown
interface ethernet4 auto shutdown
interface ethernet5 auto shutdown
nameif ethernet0 outside security0
nameif ethernet1 inside security100
nameif ethernet2 intf2 security4
nameif ethernet3 intf3 security6
nameif ethernet4 intf4 security8
nameif ethernet5 intf5 security10
enable password 8Ry2YjIyt7RRXU24 encrypted
passwd 2KFQnbNIdI.2KYOU encrypted
hostname Lion
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

!--- Defines interesting traffic that is protected by the IPsec tunnel.

access-list 101 permit gre 192.168.4.0 255.255.255.0 192.168.3.0 255.255.255.0


!--- Do not perform NAT for traffic to other PIX Firewall.

access-list nonat permit ip 192.168.4.0 255.255.255.0 192.168.3.0 255.255.255.0
pager lines 24
mtu outside 1500
mtu inside 1500
mtu intf2 1500
mtu intf3 1500
mtu intf4 1500
mtu intf5 1500
ip address outside 10.64.10.16 255.255.255.224
ip address inside 192.168.4.1 255.255.255.0

!--- Output suppressed.

global (outside) 1 interface

!--- Do not Network Address Translate (NAT) traffic.

nat (inside) 0 access-list nonat
nat (inside) 1 0.0.0.0 0.0.0.0 0 0 
route outside 0.0.0.0 0.0.0.0 10.64.10.1 1
timeout xlate 3:00:00
timeout conn 1:00:00 half-closed 0:10:00 udp 0:02:00 rpc 0:10:00 h323 0:05:00 s0
timeout h323 0:05:00 mgcp 0:05:00 sip 0:30:00 sip_media 0:02:00
timeout sip-disconnect 0:02:00 sip-invite 0:03:00
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

!--- Trust IPSec traffic and avoid going through !--- access control lists (ACLs)/NAT.

sysopt connection permit-ipsec


!--- IPsec configuration.

crypto ipsec transform-set pixset esp-des esp-md5-hmac 
crypto map pixmap 20 ipsec-isakmp
crypto map pixmap 20 match address 101
crypto map pixmap 20 set peer 10.65.10.15 
crypto map pixmap 20 set transform-set pixset
crypto map pixmap interface outside
isakmp enable outside

!--- IKE parameters.

isakmp key ******** address 10.65.10.15 netmask 255.255.255.255 
isakmp identity address
isakmp policy 20 authentication pre-share
isakmp policy 20 encryption des
isakmp policy 20 hash md5
isakmp policy 20 group 1
isakmp policy 20 lifetime 3600
telnet timeout 5
ssh 10.104.205.124 255.255.255.255 outside
ssh timeout 5
terminal width 80
Cryptochecksum:d39b3d449563c7cd434b43f82f0f0a21
: end

PIX Version 6.3(5)
interface ethernet0 auto
interface ethernet1 auto
interface ethernet2 auto shutdown
interface ethernet3 auto shutdown
interface ethernet4 auto shutdown
interface ethernet5 auto shutdown
nameif ethernet0 outside security0
nameif ethernet1 inside security100
nameif ethernet2 intf2 security4
nameif ethernet3 intf3 security6
nameif ethernet4 intf4 security8
nameif ethernet5 intf5 security10
enable password 8Ry2YjIyt7RRXU24 encrypted
passwd 2KFQnbNIdI.2KYOU encrypted
hostname Tiger
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
access-list 101 permit gre 192.168.3.0 255.255.255.0 192.168.4.0 255.255.255.0 

access-list nonat permit ip 192.168.3.0 255.255.255.0 192.168.4.0 255.255.255.0 
mtu outside 1500
mtu inside 1500
mtu intf2 1500
mtu intf3 1500
mtu intf4 1500
mtu intf5 1500
ip address outside 10.65.10.15 255.255.255.224
ip address inside 192.168.3.1 255.255.255.0

!--- Output suppressed.

global (outside) 1 interface

!--- Do not NAT traffic.

nat (inside) 0 access-list nonat
nat (inside) 1 0.0.0.0 0.0.0.0 0 0
route outside 0.0.0.0 0.0.0.0 10.64.10.1 1
timeout xlate 3:00:00
timeout conn 1:00:00 half-closed 0:10:00 udp 0:02:00 rpc 0:10:00 h323 0:05:00 s0
timeout h323 0:05:00 mgcp 0:05:00 sip 0:30:00 sip_media 0:02:00
timeout sip-disconnect 0:02:00 sip-invite 0:03:00
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 parameters.

crypto ipsec transform-set pixset esp-des esp-md5-hmac 
crypto map pixmap 20 ipsec-isakmp
crypto map pixmap 20 match address 101
crypto map pixmap 20 set peer 10.64.10.16
crypto map pixmap 20 set transform-set pixset
crypto map pixmap interface outside

!--- IKE parameters.

isakmp enable outside
isakmp key ******** address 10.64.10.16 netmask 255.255.255.255 
isakmp identity address
isakmp policy 20 authentication pre-share
isakmp policy 20 encryption des
isakmp policy 20 hash md5
isakmp policy 20 group 1
isakmp policy 20 lifetime 3600
telnet timeout 5
ssh timeout 5
terminal width 80
Cryptochecksum:a0a7ac847b05d9d080d1c442ef053a0b
: end

version 12.4
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname rodney
!
memory-size iomem 15
ip subnet-zero
!
ip audit notify log
ip audit po max-events 100
!
!
interface Loopback1
ip address 10.22.22.22 255.255.255.0
!
interface Tunnel0
ip address 10.1.1.2 255.255.255.0

!--- Tunnel source.

tunnel source Ethernet0/1

!--- Tunnel destination.

tunnel destination 192.168.3.2
!
interface Ethernet0/0
no ip address
!
interface Serial0/0
no ip address
shutdown
!
interface Ethernet0/1
ip address 192.168.4.2 255.255.255.0
!
interface Serial0/1
no ip address
shutdown
!
router ospf 22
log-adjacency-changes
network 10.1.1.0 0.0.0.255 area 0
network 10.22.22.0 0.0.0.255 area 0
!
ip classless
ip route 0.0.0.0 0.0.0.0 192.168.4.1

!--- The 10.11.11.0 traffic is passed through !--- the GRE tunnel.

ip route 10.11.11.0 255.255.255.0 Tunnel0
no ip http server
!
line con 0
line aux 0
line vty 0 4
login 
!
end!
End

version 12.4
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname house
!
ip subnet-zero
no ip domain-lookup
!

!
interface Loopback1
ip address 10.11.11.11 255.255.255.0
!
interface Tunnel0
ip address 10.1.1.1 255.255.255.0

!--- Tunnel source.

tunnel source FastEthernet0/1

!--- Tunnel destination.

tunnel destination 192.168.4.2
!
interface FastEthernet0/0
no ip address
shutdown
duplex auto
speed auto
!
interface FastEthernet0/1
ip address 192.168.3.2 255.255.255.0
duplex auto
speed auto
! 
interface FastEthernet4/0
no ip address
shutdown
duplex auto
speed auto
!
router ospf 11
log-adjacency-changes
network 10.1.1.0 0.0.0.255 area 0
network 10.11.11.0 0.0.0.255 area 0
!
ip classless
ip route 0.0.0.0 0.0.0.0 192.168.3.1

!--- The 10.22.22.0 traffic is passed through !--- the GRE tunnel.

ip route 10.22.22.0 255.255.255.0 Tunnel0
ip http server
!
line con 0
line aux 0
line vty 0 4

Verify

There is currently no verification procedure available for this configuration.

Troubleshoot

This section provides information you can use to troubleshoot your configuration.

Refer to Troubleshooting the PIX to Pass Data Traffic on an Established IPSec Tunnel for additional information on troubleshooting a PIX and IPsec tunnel.

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.

PIX IPsec Good Debug

• show crypto isakmp sa—Shows the Internet Security Association Management Protocol (ISAKMP) Security Association (SA) built between peers.

  Lion#show crypto isakmp sa
  Total : 1
  Embryonic : 0
  dst src state pending created
  10.65.10.15 10.64.10.16 QM_IDLE 0 1
  
  
  Tiger#show crypto isakmp sa
  Total SAs : 1
  Embryonic : 0
  dst src state pending created
  10.65.10.15 10.64.10.16 QM_IDLE 0 1

• show crypto engine connection active—Shows each Phase 2 SA built and the amount of traffic sent.

  Lion#show crypto engine connection active
  Crypto Engine Connection Map:
  size = 8, free = 6, used = 2, active = 2
  
  
  Tiger#show crypto engine connection active
  Crypto Engine Connection Map:
  size = 8, free = 6, used = 2, active = 2

• show debug—Displays the debug output.

  Lion#show debug
  debug crypto ipsec 
  debug crypto isakmp 
  debug crypto engine
  crypto_isakmp_process_block: src 10.65.10.15, dest 10.64.10.16
  OAK_MM exchange
  ISAKMP (0): processing SA payload. message ID = 0
  
  ISAKMP (0): Checking ISAKMP transform 1 against priority 20 policy
  ISAKMP: encryption DES-CBC
  ISAKMP: hash MD5
  ISAKMP: default group 1
  ISAKMP: auth pre-share
  ISAKMP: life type in seconds
  ISAKMP: life duration (basic) of 3600
  ISAKMP (0): atts are acceptable. Next payload is 0
  ISAKMP (0): SA is doing pre-shared key authentication using id type ID_IPV4_ADDR
  return status is IKMP_NO_ERROR# 
  crypto_isakmp_process_block: src 10.65.10.15, dest 10.64.10.16
  OAK_MM exchange
  ISAKMP (0): processing KE payload. message ID = 0
  
  ISAKMP (0): processing NONCE payload. message ID = 0
  
  ISAKMP (0): processing vendor id payload
  
  ISAKMP (0): speaking to another IOS box!
  
  ISAKMP (0): ID payload
  next-payload : 8
  type : 1
  protocol : 17
  port : 500
  length : 8
  ISAKMP (0): Total payload length: 12
  return status is IKMP_NO_ERROR
  crypto_isakmp_process_block: src 10.65.10.15, dest 10.64.10.16
  OAK_MM exchange
  ISAKMP (0): processing ID payload. message ID = 0
  ISAKMP (0): processing HASH payload. message ID = 0
  ISAKMP (0): SA has been authenticated
  
  ISAKMP (0): beginning Quick Mode exchange, M-ID of 1220019031:48b80357IPSEC(key.
  IPSEC(spi_response): getting spi 0xa67177c5(2792454085) for SA 
  from 10.65.10.15 to 10.64.10.16 for prot 3
  
  return status is IKMP_NO_ERROR
  crypto_isakmp_process_block: src 10.65.10.15, dest 10.64.10.16
  OAK_QM exchange
  oakley_process_quick_mode:
  OAK_QM_IDLE
  ISAKMP (0): processing SA payload. message ID = 1220019031
  
  ISAKMP : Checking IPSec proposal 1
  
  ISAKMP: transform 1, ESP_DES
  ISAKMP: attributes in transform:
  ISAKMP: encaps is 1
  ISAKMP: SA life type in seconds
  ISAKMP: SA life duration (basic) of 28800
  ISAKMP: SA life type in kilobytes
  ISAKMP: SA life duration (VPI) of 0x0 0x46 0x50 0x0 
  ISAKMP: authenticator is HMAC-MD5
  ISAKMP (0): atts are acceptable.IPSEC(validate_proposal_request): proposal part,
  (key eng. msg.) dest= 10.65.10.15, src= 10.64.10.16, 
  dest_proxy= 192.168.3.0/255.255.255.0/0/0 (type=4), 
  src_proxy= 192.168.4.0/255.255.255.0/0/0 (type=4),
  protocol= ESP, transform= esp-des esp-md5-hmac , 
  lifedur= 0s and 0kb, 
  spi= 0x0(0), conn_id= 0, keysize= 0, flags= 0x4
  
  ISAKMP (0): processing NONCE payload. message ID = 1220019031
  
  ISAKMP (0): processing ID payload. message ID = 1220019031
  ISAKMP (0): processing ID payload. message ID = 1220019031map_alloc_entry: allo2
  map_alloc_entry: allocating entry 1
  
  ISAKMP (0): Creating IPSec SAs
  inbound SA from 10.65.10.15 to 10.64.10.16 (proxy 192.168.3)
  has spi 2792454085 and conn_id 2 and flags 4
  lifetime of 28800 seconds
  lifetime of 4608000 kilobytes
  outbound SA from 10.64.10.16 to 10.65.10.15 (proxy 192.168.)
  has spi 285493108 and conn_id 1 and flags 4
  lifetime of 28800 seconds
  lifetime of 4608000 kilobytesIPSEC(key_engine): got a queue event...
  IPSEC(initialize_sas): ,
  (key eng. msg.) dest= 10.64.10.16, src= 10.65.10.15, 
  dest_proxy= 192.168.4.0/255.255.255.0/0/0 (type=4), 
  src_proxy= 192.168.3.0/255.255.255.0/0/0 (type=4),
  protocol= ESP, transform= esp-des esp-md5-hmac , 
  lifedur= 28800s and 4608000kb, 
  spi= 0xa67177c5(2792454085), conn_id= 2, keysize= 0, flags= 0x4
  IPSEC(initialize_sas): ,
  (key eng. msg.) src= 10.64.10.16, dest= 10.65.10.15, 
  src_proxy= 192.168.4.0/255.255.255.0/0/0 (type=4), 
  dest_proxy= 192.168.3.0/255.255.255.0/0/0 (type=4),
  protocol= ESP, transform= esp-des esp-md5-hmac , 
  lifedur= 28800s and 4608000kb, 
  spi= 0x11044774(285493108), conn_id= 1, keysize= 0, flags= 0x4
  
  return status is IKMP_NO_ERROR

Router GRE Passing Routing and Ping

• show ip route—Displays IP routing table entries.

  rodney#show ip route
  Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
  D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
  N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
  E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
  i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
  * - candidate default, U - per-user static route, o - ODR
  P - periodic downloaded static route
  
  Gateway of last resort is 192.168.4.1 to network 0.0.0.0
  
  10.0.0.0/24 is subnetted, 1 subnets
  C 10.1.1.0 is directly connected, Tunnel0
  10.0.0.0/24 is subnetted, 1 subnets
  C 10.20.20.0 is directly connected, Loopback0
  10.0.0.0/24 is subnetted, 1 subnets
  C 10.22.22.0 is directly connected, Loopback1
  C 192.168.4.0/24 is directly connected, Ethernet0/1
  10.0.0.0/24 is subnetted, 1 subnets
  S 10.10.10.0 is directly connected, Tunnel0
  10.0.0.0/32 is subnetted, 1 subnets
  O 10.11.11.11 [110/11112] via 10.1.1.1, 03:34:01, Tunnel0
  S* 0.0.0.0/0 [1/0] via 192.168.4.1
  rodney#
  rodney#ping 10.11.11.11
  
  Type escape sequence to abort.
  Sending 5, 100-byte ICMP Echos to 10.11.11.11, timeout is 2 seconds:
  !!!!!
  Success rate is 100 percent (5/5), round-trip min/avg/max = 1/2/4 ms
  
  
  
  house#show ip route
  Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
  D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area 
  N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
  E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
  i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
  * - candidate default, U - per-user static route, o - ODR
  P - periodic downloaded static route
  
  Gateway of last resort is 192.168.3.1 to network 0.0.0.0
  
  10.0.0.0/24 is subnetted, 1 subnets
  C 1.1.1.0 is directly connected, Tunnel0
  10.0.0.0/24 is subnetted, 1 subnets
  S 10.20.20.0 is directly connected, Tunnel0
  10.0.0.0/32 is subnetted, 1 subnets
  O 10.22.22.22 [110/11112] via 10.1.1.2, 03:33:39, Tunnel0
  10.0.0.0/24 is subnetted, 1 subnets
  C 10.10.10.0 is directly connected, Loopback0
  10.0.0.0/24 is subnetted, 1 subnets
  C 10.11.11.0 is directly connected, Loopback1
  C 192.168.3.0/24 is directly connected, FastEthernet0/1
  S* 0.0.0.0/0 [1/0] via 192.168.3.1
  
  house#ping 10.22.22.22
  
  Type escape sequence to abort.
  Sending 5, 100-byte ICMP Echos to 10.22.22.22, timeout is 2 seconds:
  !!!!!
  Success rate is 100 percent (5/5), round-trip min/avg/max = 1/3/4 ms

Related Information

• IPSec Negotiation/IKE Protocols
• Cisco Secure PIX Firewall Command References
• PIX Product Support
• Technical Support & Documentation - Cisco Systems