IPSec with IPv6-in-IPv4 GRE tunnel

IPSec with IPv6-in-IPv4 GRE tunnel

Theory:

RFC 4891 discusses about IPSec with IPv6-in-IPv4 tunnels. It points out two different types of threats with IPv6-in-IPv4 tunnels which mandates the use of IPSec. The two types of threats are-

1) The IPv4 source address of the encapsulating (outer) packet can be spoofed

2) The IPv6 source address of the encapsulated (inner) packet can be spoofed.

RFC 4891 discusses two ways to use IPSec- in transport and tunnel modes.

IPSec in Transport mode:

In transport mode, the IPSec ESP or AH SA are established to protect traffic with the header {IPv4 Source address, IPv4 Destination address, Protocol = 41}. On receiving an IPSec packet, the receiver applies the IPSec transform (e.g. ESP or AH) and matches the packet against Security Parameter Index (SPI) and the inbound selectors associated with the SA to verify that the packet is appropriate for the SA via which it was received. The successful verification ensures that the packet came from correct IPv4 endpoint.

The transport mode takes care of threat # 1. But IPSec in Transport mode does not verify the payload of the IPSec packet which carries IPv6 addresses. Hence, the inner payload can be spoofed. The packet will be decapsulated and accepted. This shortcoming can be mitigated by Ingress filtering which is a check to ensure packet is received on the correct interface like RPF in IP multicasting.

IPSec in Tunnel mode:

In Tunnel mode, the IPSec SA is established to protect the traffic defined by {IPv6 Source address, IPv6 Destination address}. On receiving such an IPSec packet, the receiver first applies the IPSec transform and matches the packet against SPI and inbound selectors associated with the SA. The successful verification ensures that the packet came from correct endpoint.

In tunnel mode, the outer IPv4 addresses can be spoofed and IPSec cannot detect this in tunnel mode.

Network topology:

An IPv6-in-IPv4 GRE tunnel needs to be setup between R1 & R2 router connecting the two IPv6 domains separated by an IPv4 network.

Initial configuration on R1

ipv6 unicast-routing

interface Loopback 0

 ip address 1.1.1.1 255.255.255.255

interface serial 0/0

 description IPv4 WAN Interface

 ip address 10.1.1.1 255.255.255.252

interface fastethernet 0/0

 description Internal IPv6 network

 ipv6 address CAFE:1::1/64

router ospf 1

 network 1.1.1.1 0.0.0.0 area 0

 network 10.1.1.0 0.0.0.3 area 0

Initial configuration on R2

ipv6 unicast-routing

interface Loopback 0

 ip address 2.2.2.2 255.255.255.255

interface serial 0/0

 description IPv4 WAN Interface

 ip address 10.2.2.2 255.255.255.252

interface fastethernet 0/0

 description Internal IPv6 network

 ipv6 address CAFE:2::1/64

router ospf 1

 network 2.2.2.2 0.0.0.0 area 0

 network 10.2.2.0 0.0.0.3 area 0

GRE Tunnel configuration:

A GRE tunnel is setup between R1 and R2. The tunnel interfaces will have IPv6 addresses and they belong to the same network. IPv6 traffic for remote sites is manually forwarded over GRE tunnel using an IPv6 static route.

Tunnel configuration on R1

interface Tunnel 0

 tunnel mode gre ip

 ipv6 address 2001::1/64

 tunnel source Loopback 0

 tunnel destination 2.2.2.2

ipv6 route CAFE:2::/64 2001::2

Tunnel configuration on R2

interface Tunnel 0

 tunnel mode gre ip

 ipv6 address 2001::2/64

 tunnel source Loopback 0

 tunnel destination 1.1.1.1

ipv6 route CAFE:1::/64 2001::1

When traffic is generated from R1 router's IPv6 domain towards R2 router's IPv6 network, ICMPv6 packets are encapsulated in a GRE packet (protocol= 0x2F or decimal value 47) with packet's source IP address as R1's Loopback 0 interface and destination IP address as R2's Loopback 0 interface. At R2 router, these GRE packets are decapsulated and forwarded to the correct destination.

GRE Ping results

R1# ping  CAFE:2::1 source fa 0/0

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to CAFE:2::1, timeout is 2 seconds:

Packet sent with a source address of CAFE:1::1

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 44/64/96 ms

R1# debug ip packet detail

IP: s=1.1.1.1 (Tunnel0), d=2.2.2.2 (Serial0/0), len 124, sending, proto=47

IP: s=1.1.1.1 (Tunnel0), d=2.2.2.2 (Serial0/0), len 124, sending, proto=47

IP: s=1.1.1.1 (Tunnel0), d=2.2.2.2 (Serial0/0), len 124, sending, proto=47

IP: s=1.1.1.1 (Tunnel0), d=2.2.2.2 (Serial0/0), len 124, sending, proto=47

IP: s=1.1.1.1 (Tunnel0), d=2.2.2.2 (Serial0/0), len 124, sending, proto=47

IPSec over IPv6-in-IPv4 GRE tunnel:

Over this GRE tunnel, IPSec is configured using static crypto-map to encrypt the traffic on the GRE tunnel. This essentially adds extra overhead since the GRE packet is encapsulated by ESP (protocol value 50). All the traffic that travels over the GRE tunnel get encrypted hence no access-list is configured to match interesting traffic. Also, the peer address is set to the Loopback 0 interfaces of the routers since they are used as the source IP addresses for the GRE tunnel.

IPSec configuration on R1

crypto isakmp policy 10

 encryption des

 authentication pre-share

 hash md5

 group 2

crypto isakmp key 0 MY_K3Y address 2.2.2.2

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

crypto ipsec profile PROFILE

 set transform-set TS

interface tunnel 0

 tunnel protection ipsec profile PROFILE

IPSec configuration on R2

crypto isakmp policy 10

 encryption des

 authentication pre-share

 hash md5

 group 2

crypto isakmp key 0 MY_K3Y address 1.1.1.1

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

crypto ipsec profile PROFILE

 set transform-set TS

interface tunnel 0

 tunnel protection ipsec profile PROFILE

When traffic is generated from R1 router's IPv6 domain towards R2 router's IPv6 network, ICMPv6 packets are encapsulated in GRE packets, which are then encapsulated in an ESP packet. R1 router also initiates an IKE negotiation with R2 router, meanwhile all packets are dropped.

The debugging on R2 router shows how it negotiates SA with R1 router. It shows that when R2 router receives a packet from 1.1.1.1 peer, it checks to see if it has a pre-shared key. It initiates IKE Phase 1 during which it checks whether the policy sent by R1 matches any of its policy and if it agrees to the policy. After successful IKE Phase 1, it initiates IKE Phase 2 during which it checks IPSec transform-set. After successful transform-set negotiation IKE Phase 2 is completed after which communication is possible.

"debug crypto isakmp" on R2

ISAKMP (0:0): received packet from 1.1.1.1 dport 500 sport 500 Global (N) NEW SA

ISAKMP: Created a peer struct for 1.1.1.1, peer port 500

ISAKMP: New peer created peer = 0x64BB250C peer_handle = 0x80000004

ISAKMP: Locking peer struct 0x64BB250C, IKE refcount 1 for crypto_isakmp_process_block

ISAKMP: local port 500, remote port 500 insert sa successfully sa = 64BB6094

ISAKMP:(0:0:N/A:0):Input = IKE_MESG_FROM_PEER, IKE_MM_EXCH

ISAKMP:(0:0:N/A:0):Old State = IKE_READY  New State = IKE_R_MM1

ISAKMP:(0:0:N/A:0): processing SA payload. message ID = 0

ISAKMP:(0:0:N/A:0): processing vendor id payload

ISAKMP:(0:0:N/A:0): vendor ID seems Unity/DPD but major 245 mismatch

ISAKMP (0:0): vendor ID is NAT-T v7

ISAKMP:(0:0:N/A:0): processing vendor id payload

ISAKMP:(0:0:N/A:0): vendor ID seems Unity/DPD but major 157 mismatch

ISAKMP:(0:0:N/A:0): vendor ID is NAT-T v3

ISAKMP:(0:0:N/A:0): processing vendor id payload

ISAKMP:(0:0:N/A:0): vendor ID seems Unity/DPD but major 123 mismatch

ISAKMP:(0:0:N/A:0): vendor ID is NAT-T v2

ISAKMP:(0:0:N/A:0):found peer pre-shared key matching 1.1.1.1

ISAKMP:(0:0:N/A:0): local preshared key found

ISAKMP : Scanning profiles for xauth ...

ISAKMP:(0:0:N/A:0):Checking ISAKMP transform 1 against priority 10 policy

ISAKMP:      encryption DES-CBC

ISAKMP:      hash MD5

ISAKMP:      default group 2

ISAKMP:      auth pre-share

ISAKMP:      life type in seconds

ISAKMP:      life duration (VPI) of  0x0 0x1 0x51 0x80

ISAKMP:(0:0:N/A:0):atts are acceptable. Next payload is 0

ISAKMP:(0:1:SW:1): processing vendor id payload

ISAKMP:(0:1:SW:1): vendor ID seems Unity/DPD but major 245 mismatch

ISAKMP (0:134217729): vendor ID is NAT-T v7

ISAKMP:(0:1:SW:1): processing vendor id payload

ISAKMP:(0:1:SW:1): vendor ID seems Unity/DPD but major 157 mismatch

ISAKMP:(0:1:SW:1): vendor ID is NAT-T v3

ISAKMP:(0:1:SW:1): processing vendor id payload

ISAKMP:(0:1:SW:1): vendor ID seems Unity/DPD but major 123 mismatch

ISAKMP:(0:1:SW:1): vendor ID is NAT-T v2

ISAKMP:(0:1:SW:1):Input = IKE_MESG_INTERNAL, IKE_PROCESS_MAIN_MODE

ISAKMP:(0:1:SW:1):Old State = IKE_R_MM1  New State = IKE_R_MM1

ISAKMP:(0:1:SW:1): constructed NAT-T vendor-07 ID

ISAKMP:(0:1:SW:1): sending packet to 1.1.1.1 my_port 500 peer_port 500 (R) MM_SA_SETUP

ISAKMP:(0:1:SW:1):Input = IKE_MESG_INTERNAL, IKE_PROCESS_COMPLETE

ISAKMP:(0:1:SW:1):Old State = IKE_R_MM1  New State = IKE_R_MM2

ISAKMP (0:134217729): received packet from 1.1.1.1 dport 500 sport 500 Global (R) MM_SA_SETUP

ISAKMP:(0:1:SW:1):Input = IKE_MESG_FROM_PEER, IKE_MM_EXCH

ISAKMP:(0:1:SW:1):Old State = IKE_R_MM2  New State = IKE_R_MM3

ISAKMP:(0:1:SW:1): processing KE payload. message ID = 0

ISAKMP:(0:1:SW:1): processing NONCE payload. message ID =0

ISAKMP:(0:1:SW:1):found peer pre-shared key matching 1.1.1.1

ISAKMP:(0:1:SW:1):SKEYID state generated

ISAKMP:(0:1:SW:1): processing vendor id payload

ISAKMP:(0:1:SW:1): vendor ID is Unity

ISAKMP:(0:1:SW:1): processing vendor id payload

ISAKMP:(0:1:SW:1): vendor ID is DPD

ISAKMP:(0:1:SW:1): processing vendor id payload

ISAKMP:(0:1:SW:1): speaking to another IOS box!

ISAKMP:(0:1:SW:1):Input = IKE_MESG_INTERNAL, IKE_PROCESS_MAIN_MODE

ISAKMP:(0:1:SW:1):Old State = IKE_R_MM3  New State = IKE_R_MM3

ISAKMP:(0:1:SW:1): sending packet to 1.1.1.1 my_port 500 peer_port 500 (R) MM_KEY_EXCH

ISAKMP:(0:1:SW:1):Input = IKE_MESG_INTERNAL, IKE_PROCESS_COMPLETE

ISAKMP:(0:1:SW:1):Old State = IKE_R_MM3  New State = IKE_R_MM4

ISAKMP (0:134217729): received packet from 1.1.1.1 dport 500 sport 500 Global (R) MM_KEY_EXCH

ISAKMP:(0:1:SW:1):Input = IKE_MESG_FROM_PEER, IKE_MM_EXCH

ISAKMP:(0:1:SW:1):Old State = IKE_R_MM4  New State = IKE_R_MM5

ISAKMP:(0:1:SW:1): processing ID payload. message ID = 0

ISAKMP (0:134217729): ID payload

        next-payload : 8

        type         : 1

        address      : 1.1.1.1

        protocol     : 17

        port         : 500

        length       : 12

ISAKMP:(0:1:SW:1):: peer matches *none* of the profiles

ISAKMP:(0:1:SW:1): processing HASH payload. message ID = 0

ISAKMP:(0:1:SW:1): processing NOTIFY INITIAL_CONTACT protocol 1

        spi 0, message ID = 0, sa = 64BB6094

ISAKMP:(0:1:SW:1):SA authentication status:authenticated

ISAKMP:(0:1:SW:1): Process initial contact,bring down existing phase 1 and 2 SA's with local 2.2.2.2 remote 1.1.1.1 remote port 500

ISAKMP:(0:1:SW:1):SA authentication status: authenticated

ISAKMP:(0:1:SW:1):SA has been authenticated with 1.1.1.1

ISAKMP: Trying to insert a peer 2.2.2.2/1.1.1.1/500/,  and inserted successfully 64BB250C.

ISAKMP:(0:1:SW:1):Input = IKE_MESG_INTERNAL, IKE_PROCESS_MAIN_MODE

ISAKMP:(0:1:SW:1):Old State = IKE_R_MM5  New State = IKE_R_MM5

ISAKMP:(0:1:SW:1):SA is doing pre-shared key authentication using id type ID_IPV4_ADDR

ISAKMP (0:134217729): ID payload

        next-payload : 8

        type         : 1

        address      : 2.2.2.2

        protocol     : 17

        port         : 500

        length       : 12

ISAKMP:(0:1:SW:1):Total payload length: 12

ISAKMP:(0:1:SW:1): sending packet to 1.1.1.1 my_port 500 peer_port 500 (R) MM_KEY_EXCH

ISAKMP:(0:1:SW:1):Input = IKE_MESG_INTERNAL, IKE_PROCESS_COMPLETE

ISAKMP:(0:1:SW:1):Old State = IKE_R_MM5  New State = IKE_P1_COMPLETE

ISAKMP:(0:1:SW:1):Input = IKE_MESG_INTERNAL, IKE_PHASE1_COMPLETE

ISAKMP:(0:1:SW:1):Old State = IKE_P1_COMPLETE  New State = IKE_P1_COMPLETE

ISAKMP (0:134217729): received packet from 1.1.1.1 dport 500 sport 500 Global (R) QM_IDLE

ISAKMP: set new node 1046004050 to QM_IDLE

ISAKMP:(0:1:SW:1): processing HASH payload. message ID = 1046004050

ISAKMP:(0:1:SW:1): processing SA payload. message ID = 1046004050

ISAKMP:(0:1:SW:1):Checking IPSec proposal 1

ISAKMP: transform 1, ESP_DES

ISAKMP:   attributes in transform:

ISAKMP:      encaps is 1 (Tunnel)

ISAKMP:      SA life type in seconds

ISAKMP:      SA life duration (basic) of 3600

ISAKMP:      SA life type in kilobytes

ISAKMP:      SA life duration (VPI) of  0x0 0x46 0x50 0x0

ISAKMP:      authenticator is HMAC-MD5

ISAKMP:(0:1:SW:1):atts are acceptable.

ISAKMP:(0:1:SW:1): processing NONCE payload. message ID =1046004050

ISAKMP:(0:1:SW:1): processing ID payload. message ID = 1046004050

ISAKMP:(0:1:SW:1): processing ID payload. message ID = 1046004050

ISAKMP:(0:1:SW:1): asking for 1 spis from ipsec

ISAKMP:(0:1:SW:1):Node 1046004050, Input = IKE_MESG_FROM_PEER, IKE_QM_EXCH

ISAKMP:(0:1:SW:1):Old State = IKE_QM_READY  New State = IKE_QM_SPI_STARVE

ISAKMP: received ke message (2/1)

ISAKMP: Locking peer struct 0x64BB250C, IPSEC refcount 1 for for stuff_ke

ISAKMP:(0:1:SW:1): Creating IPSec SAs

        inbound SA from 1.1.1.1 to 2.2.2.2 (f/i)  0/ 0

        (proxy 1.1.1.1 to 2.2.2.2)

        has spi 0x4F11F20E and conn_id 0 and flags 2

        lifetime of 3600 seconds

        lifetime of 4608000 kilobytes

        has client flags 0x0

        outbound SA from 2.2.2.2 to 1.1.1.1 (f/i) 0/0

        (proxy 2.2.2.2 to 1.1.1.1)

        lifetime of 3600 seconds

        lifetime of 4608000 kilobytes

        has client flags 0x0

ISAKMP:(0:1:SW:1): sending packet to 1.1.1.1 my_port 500 peer_port 500 (R) QM_IDLE

ISAKMP:(0:1:SW:1):Node 1046004050, Input = IKE_MESG_FROM_IPSEC, IKE_SPI_REPLY

ISAKMP:(0:1:SW:1):Old State = IKE_QM_SPI_STARVE  New State = IKE_QM_R_QM2

ISAKMP: Locking peer struct 0x64BB250C, IPSEC refcount 2 for from create_transforms

ISAKMP: Unlocking IPSEC struct 0x64BB250C from create_transforms, count 1

ISAKMP (0:134217729): received packet from 1.1.1.1 dport 500 sport 500 Global (R) QM_IDLE

ISAKMP:(0:1:SW:1):deleting node 1046004050 error FALSE reason "QM done (await)"

ISAKMP:(0:1:SW:1):Node 1046004050, Input = IKE_MESG_FROM_PEER, IKE_QM_EXCH

ISAKMP:(0:1:SW:1):Old State = IKE_QM_R_QM2  New State = IKE_QM_PHASE2_COMPLETE

The show crypto isakmp peer [detail] command shows peer description.

show crypto isakmp peers

R1# show crypto isakmp peers

Peer: 2.2.2.2 Port: 500 Local: 1.1.1.1

 Phase1 id: 2.2.2.2

The show crypto session detail command provides details on currently active crypto sessions.

show crypto session detail

R1# show crypto session detail

Crypto session current status

Code: C - IKE Configuration mode, D - Dead Peer Detection

K - Keepalives, N - NAT-traversal, X - IKE Extended Authentication

Interface: Tunnel0

Session status: UP-ACTIVE

Peer: 2.2.2.2 port 500 fvrf: (none) ivrf: (none)

      Phase1_id: 2.2.2.2

      Desc: (none)

  IKE SA: local 1.1.1.1/500 remote 2.2.2.2/500 Active

          Capabilities:(none) connid:1 lifetime:23:59:34

  IPSEC FLOW: permit 47 host 1.1.1.1 host 2.2.2.2

        Active SAs: 2, origin: crypto map

        Inbound:  #pkts dec'ed 9 drop 0 life (KB/Sec) 4586052/3575

        Outbound: #pkts enc'ed 9 drop 11 life (KB/Sec) 4586052/3575

The show crypto isakmp sa and show crypto ipsec sa commands show IKE Phase 1 and Phase 2 SA respectively.

IKE Phase 1 & 2 SA

R1# show crypto isakmp sa

dst             src             state          conn-id slot status

2.2.2.2         1.1.1.1         QM_IDLE              1    0 ACTIVE

R1# show crypto ipsec sa

interface: Tunnel0

    Crypto map tag: Tunnel0-head-0, local addr 1.1.1.1

   protected vrf: (none)

   local  ident (addr/mask/prot/port): (1.1.1.1/255.255.255.255/47/0)

   remote ident (addr/mask/prot/port): (2.2.2.2/255.255.255.255/47/0)

   current_peer 2.2.2.2 port 500

     PERMIT, flags={origin_is_acl,}

    #pkts encaps: 9, #pkts encrypt: 9, #pkts digest: 9

    #pkts decaps: 9, #pkts decrypt: 9, #pkts verify: 9

    #pkts compressed: 0, #pkts decompressed: 0

    #pkts not compressed: 0, #pkts compr. failed: 0

    #pkts not decompressed: 0, #pkts decompress failed: 0

    #send errors 11, #recv errors 0

     local crypto endpt.: 1.1.1.1, remote crypto endpt.: 2.2.2.2

     path mtu 1514, ip mtu 1514, ip mtu idb Loopback0

     current outbound spi: 0x4F11F20E(1326576142)

     inbound esp sas:

      spi: 0x3861DD57(945937751)

        transform: esp-des esp-md5-hmac ,

        in use settings ={Tunnel, }

        conn id: 2001, flow_id: SW:1, crypto map: Tunnel0-head-0

        sa timing: remaining key lifetime (k/sec): (4586052/3201)

        IV size: 8 bytes

        replay detection support: Y

        Status: ACTIVE

     inbound ah sas:

     inbound pcp sas:

     outbound esp sas:

      spi: 0x4F11F20E(1326576142)

        transform: esp-des esp-md5-hmac ,

        in use settings ={Tunnel, }

        conn id: 2002, flow_id: SW:2, crypto map: Tunnel0-head-0

        sa timing: remaining key lifetime (k/sec): (4586052/3200)

        IV size: 8 bytes

        replay detection support: Y

        Status: ACTIVE

     outbound ah sas:

     outbound pcp sas:

The following output shows R1 sending ESP encapsulated packets (protocol 50).

debug ip packet detail

IP: tableid=0, s=1.1.1.1 (local), d=2.2.2.2 (Serial0/0), routed via FIB

IP: s=1.1.1.1 (local), d=2.2.2.2 (Serial0/0), g=10.1.1.2,len 176, forward, proto=50

IP: tableid=0, s=2.2.2.2 (Serial0/0), d=1.1.1.1 (Loopback0), routed via RIB

IP: s=2.2.2.2 (Serial0/0), d=1.1.1.1, len 124, rcvd 4, proto=47

IP: tableid=0, s=1.1.1.1 (local), d=2.2.2.2 (Serial0/0), routed via FIB

IP: s=1.1.1.1 (local), d=2.2.2.2 (Serial0/0), g=10.1.1.2,len 176, forward, proto=50

IP: tableid=0, s=2.2.2.2 (Serial0/0), d=1.1.1.1 (Loopback0), routed via RIB

IP: s=2.2.2.2 (Serial0/0), d=1.1.1.1, len 124, rcvd 4, proto=47

IP: tableid=0, s=1.1.1.1 (local), d=2.2.2.2 (Serial0/0), routed via FIB

IP: s=1.1.1.1 (local), d=2.2.2.2 (Serial0/0), g=10.1.1.2,len 176, forward, proto=50

IP: tableid=0, s=2.2.2.2 (Serial0/0), d=1.1.1.1 (Loopback0), routed via RIB

IP: s=2.2.2.2 (Serial0/0), d=1.1.1.1, len 124, rcvd 4, proto=47

IP: tableid=0, s=1.1.1.1 (local), d=2.2.2.2 (Serial0/0), routed via FIB

IP: s=1.1.1.1 (local), d=2.2.2.2 (Serial0/0), g=10.1.1.2,len 176, forward, proto=50

IP: tableid=0, s=2.2.2.2 (Serial0/0), d=1.1.1.1 (Loopback0), routed via RIB

IP: s=2.2.2.2 (Serial0/0), d=1.1.1.1, len 124, rcvd 4, proto=47

IP: tableid=0, s=1.1.1.1 (local), d=2.2.2.2 (Serial0/0), routed via FIB

IP: s=1.1.1.1 (local), d=2.2.2.2 (Serial0/0), g=10.1.1.2,len 176, forward, proto=50

IP: tableid=0, s=2.2.2.2 (Serial0/0), d=1.1.1.1 (Loopback0), routed via RIB

IP: s=2.2.2.2 (Serial0/0), d=1.1.1.1, len 124, rcvd 4, proto=47

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