MSR5620 双出口配置IPSec vpn失败经验案例

两台MSR5620作为出口设备，分别连接两根外网线，通过公网建立IPSec vpn。相关配置完成后，感兴趣流地址互ping不通。两台设备的display ike sa显示都为unknown，ike阶段都没有建立起来：

RT1：

< RT1>display ike sa

Connection-ID   Remote      Flag        DOI   

------------------------------------------------------------

   117    180.X.X.166    Unknown     IPsec 

RT2：

< RT2>display ike sa

Connection-ID   Remote       Flag        DOI   

------------------------------------------------------------

   925    140.X.X.195    Unknown     IPsec  

1、两台设备公网地址互通的前提下，检查两端配置：

RT1：

#

interface LoopBack70

 ip address 10.70.0.1 255.255.255.0

#

interface GigabitEthernet2/0/2

 ip address 140.X.X.195 255.255.255.0

 nat outbound 3001

 ipsec apply policy sq

#

ip route-static 10.60.0.1 32 140.X.X.192

#

acl advanced 3001

 rule 12 deny ip source 10.70.0.1 0 destination 10.60.0.1 0

 rule 100 permit ip

#

acl advanced 3012

 rule 55 permit ip source 10.70.0.1 0 destination 10.60.0.1 0

#

ipsec transform-set 1

 esp encryption-algorithm 3des-cbc

 esp authentication-algorithm md5

#

ipsec policy sq 1 isakmp

 transform-set 1

 security acl 3012

 local-address 140.X.X.195

 remote-address 180.X.X.166

 ike-profile sq

#

 ike identity fqdn dx

#

ike profile sq

 keychain sq

 local-identity address 140.X.X.195

 match remote identity address 180.X.X.166 255.255.255.255

 proposal 1

#

ike proposal 1

 encryption-algorithm 3des-cbc

 dh group2

 authentication-algorithm md5

#

ike keychain sq

 pre-shared-key address 180.X.X.166 255.255.255.255 key cipher $c$3$3M1ZR4VWG/7x81MQa+anzqKNObKUP1r8CVTx8=

#

RT2：

RT2配置除了相关地址与RT1不同，其他相关参数均一致。

2、核对两端IPSec vpn的配置无误，此时在RT2上开启debugging ike sa以及debugging ipsec sa，相关报错如下：

*Sep 10 16:47:09:053 2018 RT2 IKE/7/EVENT: Phase1 process started.

*Sep 10 16:47:09:054 2018 RT2 IKE/7/PACKET: vrf = 0, local = 180.X.X.166, remote = 140.X.X.195/500

Collision of phase 1 negotiation is found.

RT2收到了来自RT1的IKE报文，在IKE协商过程中提示了冲突。在设备上开启debugging ip packet查看数据包交互情况：

*Sep 10 16:47:22:721 2018 RT2 IPFW/7/IPFW_PACKET:

Receiving, interface = GigabitEthernet2/0/1, version = 4, headlen = 20, tos = 252,

pktlen = 204, pktid = 65, offset = 0, ttl = 254, protocol =17

checksum = 50690, s = 140.X.X.195, d = 180.X.X.166

prompt: Receiving IP packet.

* Sep 10 16:47:22:721 2018 RT2 IPFW/7/IPFW_PACKET:

Sending, interface = GigabitEthernet2/0/3, version = 4, headlen= 20, tos = 252,

pktlen = 144, pktid = 60, offset = 0, ttl = 255, protocol =17

checksum = 50499, s = 180.X.X.166, d = 140.X.X.195

prompt: Sending the packet from local at GigabitEthernet2/0/3

可以看出数据包从GigabitEthernet2/0/1接收，结果从GigabitEthernet2/0/3发出。在RT2上查看路由发现：

ip route-static 0.0.0.0 0 210.X.X.17

ip route-static 0.0.0.0 0 180.X.X.165 preference 70

从这里可以发现问题所在，当10.70.0.1去ping 10.60.0.1时，感兴趣流在RT1的GigabitEthernet2/0/2口进行IPSec封装后通过公网到达RT2的GigabitEthernet2/0/1。

RT2在回应报文的时候，由于RT2配置出接口为GigabitEthernet2/0/1的默认路由优先级比出接口为GigabitEthernet2/0/3的优先级低，数据包优先从GigabitEthernet2/0/3发出，路径不一致导致协商冲突。

在RT2上配置去往140.X.X.195的明细路由，下一跳指向180.X.X.165，此时ike sa和ipsec sa可以正常建立。

display ike sa

Connection-ID   Remote     Flag      DOI   

---------------------------------------------------------

 116     180.X.X.166     RD      IPsec 

Flags:

RD--READY RL--REPLACED FD-FADING RK-REKEY

display ipsec sa

  -----------------------------

  IPsec policy: sq

  Sequence number: 1

  Mode: ISAKMP

  -----------------------------

    Tunnel id: 0

    Encapsulation mode: tunnel

    Perfect Forward Secrecy:

    Inside VPN:

    Extended Sequence Numbers enable: N

    Traffic Flow Confidentiality enable: N

    Path MTU: 1444

    Tunnel:

        local address: 140.X.X.195

        remote address: 180.X.X.166

    Flow:

        sour addr: 10.70.0.1/255.255.255.255  port: 0  protocol: ip

        dest addr: 10.60.0.1/255.255.255.255  port: 0  protocol: ip

    [Inbound ESP SAs]

      SPI: 1628414150 (0x610fa0c6)

      Connection ID: 545460846593

      Transform set: ESP-ENCRYPT-3DES-CBC ESP-AUTH-MD5

      SA duration (kilobytes/sec): 1843200/3600

      SA remaining duration (kilobytes/sec): 1843199/3299

      Max received sequence-number: 4

      Anti-replay check enable: Y

      Anti-replay window size: 64

      UDP encapsulation used for NAT traversal: N

      Status: Active

    [Outbound ESP SAs]

      SPI: 2623005100 (0x9c57e1ac)

      Connection ID: 708669603842

      Transform set: ESP-ENCRYPT-3DES-CBC ESP-AUTH-MD5

      SA duration (kilobytes/sec): 1843200/3600

      SA remaining duration (kilobytes/sec): 1843199/3299

      Max sent sequence-number: 4

      UDP encapsulation used for NAT traversal: N

      Status: Active

在两台路由器上配置去往对端公网地址的明细路由，保证感兴趣流到达对端设备后从一个端口接收，并且从该端口发出。

< RT1>ip route-static 180.X.X.166 24 140.X.X.192

< RT2>ip route-static 140.X.X.195 24 180.X.X.165

在双出口的组网下，不仅仅需要配置去往对端感兴趣流的明细路由，还需要注意公网之间互通的路由选择，确保感兴趣流到达对端设备后从一个接口接收，回应报文时也从该接口发出。