我有一个简单的 VPN。我在 10.185.28.241 上有一个客户端，它从位于 10.112.18.105 的 VPN 获取虚拟 IP 10.42.42.0/24，并提供对 10.112.0.0/16 CIDR 中的机器的访问。我在 Centos 7 上运行 StrongSwan U5.3.2/K3.10.0-229.el7.x86_64。我的网络布局如下所示：
[Windows 2012 Client ]--------[VPN ]---------[Hidden network]
10.185.28.241 / 10.42.42.1 10.112.18.105 10.112.0.0/16
是的，这个网络的所有内容都是内部的。Windows 客户端实际上在 AWS 中，而 10.112 网络在我的托管中，但全部通过预先存在的站点到站点 VPN。我之所以设置它，是因为我最终希望将外部流量通过 VPN 路由回来，这样它看起来就会通过我们的托管，我们被供应商列入白名单。但我还没有到那一步。
我可以从 Windows 连接到 VPN，它通过非常花哨的 IKEv2 进行连接。当我在隐藏网络上 ping 一个 IP 时，我看到来自 tcpdump 的数据包，但 10.112.18.105 机器拒绝返回响应。
因此在 Windows 机器上我执行：
C:\temp> ping 10.112.8.102
Pinging 10.112.8.102 with 32 bytes of data:
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Ping statistics for 10.112.8.102:
Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),
C:\temp> ping 10.112.8.102
在VPN服务器上我看到：
[root@localhost strongswan]# tcpdump -n -i any host 10.112.8.102 or host 10.42.42.1
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on any, link-type LINUX_SLL (Linux cooked), capture size 65535 bytes
17:38:42.616871 IP 10.112.18.105 > 10.112.8.102: ICMP echo request, id 1, seq 161, length 40
17:38:42.617324 IP 10.112.8.102 > 10.112.18.105: ICMP echo reply, id 1, seq 161, length 40
17:38:47.280369 IP 10.42.42.1 > 10.112.8.102: ICMP echo request, id 1, seq 162, length 40
17:38:47.280457 IP 10.112.18.105 > 10.112.8.102: ICMP echo request, id 1, seq 162, length 40
17:38:47.280872 IP 10.112.8.102 > 10.112.18.105: ICMP echo reply, id 1, seq 162, length 40
17:38:52.280116 IP 10.42.42.1 > 10.112.8.102: ICMP echo request, id 1, seq 163, length 40
17:38:52.280213 IP 10.112.18.105 > 10.112.8.102: ICMP echo request, id 1, seq 163, length 40
17:38:52.280672 IP 10.112.8.102 > 10.112.18.105: ICMP echo reply, id 1, seq 163, length 40
17:38:57.279917 IP 10.42.42.1 > 10.112.8.102: ICMP echo request, id 1, seq 164, length 40
17:38:57.280018 IP 10.112.18.105 > 10.112.8.102: ICMP echo request, id 1, seq 164, length 40
17:38:57.280488 IP 10.112.8.102 > 10.112.18.105: ICMP echo reply, id 1, seq 164, length 40
^C
11 packets captured
12 packets received by filter
0 packets dropped by kernel
[root@localhost strongswan]#
回复已返回至 VPN 服务器（“10.112.8.102 > 10.112.18.105：ICMP 回显回复”），但 VPN 服务器未将响应传回客户端。我花了整整 10 个小时试图找到这个问题，但我发现很多人都遇到了类似的问题 :-(。
一些背景信息：
ipsec.conf：
config setup
charondebug="ike 2, knl 2, cfg 2, net 2, esp 2, dmn 2, mgr 2"
conn %default
keyexchange=ikev2
ike=aes128-sha256-ecp256,aes256-sha384-ecp384,aes128-sha256-modp2048,aes128-sha1-modp2048,aes256-sha384-modp4096,aes256-sha256-modp4096,aes256-sha1-modp4096,aes128-sha256-modp1536,aes128-sha1-modp1536,aes256-sha384-modp2048,aes256-sha256-modp2048,aes256-sha1-modp2048,aes128-sha256-modp1024,aes128-sha1-modp1024,aes256-sha384-modp1536,aes256-sha256-modp1536,aes256-sha1-modp1536,aes256-sha384-modp1024,aes256-sha256-modp1024,aes256-sha1-modp1024!
esp=aes128gcm16-ecp256,aes256gcm16-ecp384,aes128-sha256-ecp256,aes256-sha384-ecp384,aes128-sha256-modp2048,aes128-sha1-modp2048,aes256-sha384-modp4096,aes256-sha256-modp4096,aes256-sha1-modp4096,aes128-sha256-modp1536,aes128-sha1-modp1536,aes256-sha384-modp2048,aes256-sha256-modp2048,aes256-sha1-modp2048,aes128-sha256-modp1024,aes128-sha1-modp1024,aes256-sha384-modp1536,aes256-sha256-modp1536,aes256-sha1-modp1536,aes256-sha384-modp1024,aes256-sha256-modp1024,aes256-sha1-modp1024,aes128gcm16,aes256gcm16,aes128-sha256,aes128-sha1,aes256-sha384,aes256-sha256,aes256-sha1!
dpdaction=clear
dpddelay=300s
rekey=no
left=10.112.18.105
leftsubnet=10.112.0.0/16
leftfirewall=yes
leftcert=vpnHostCert.der
right=%any
rightdns=10.112.1.140,10.112.1.141
rightsourceip=10.42.42.0/24
conn IPSec-IKEv2
keyexchange=ikev2
auto=add
conn IPSec-IKEv2-EAP
also="IPSec-IKEv2"
rightauth=eap-mschapv2
rightsendcert=never
eap_identity=%any
conn CiscoIPSec
keyexchange=ikev1
forceencaps=yes
authby=xauthrsasig
xauth=server
auto=add
Strongswan 状态全部：
[root@localhost strongswan]# strongswan statusall
Status of IKE charon daemon (strongSwan 5.3.2, Linux 3.10.0-229.el7.x86_64, x86_64):
uptime: 26 minutes, since Apr 15 17:31:18 2016
malloc: sbrk 1630208, mmap 0, used 515488, free 1114720
worker threads: 11 of 16 idle, 5/0/0/0 working, job queue: 0/0/0/0, scheduled: 1
loaded plugins: charon aes des rc2 sha1 sha2 md4 md5 random nonce x509 revocation constraints acert pubkey pkcs1 pkcs8 pkcs12 pgp dnskey sshkey pem openssl fips-prf gmp xcbc cmac hmac ctr ccm curl attr kernel-netlink resolve socket-default farp stroke vici updown eap-identity eap-md5 eap-gtc eap-mschapv2 eap-tls eap-ttls eap-peap xauth-generic xauth-eap xauth-pam xauth-noauth dhcp
Virtual IP pools (size/online/offline):
10.42.42.0/24: 254/1/0
Listening IP addresses:
10.112.18.105
192.168.122.1
Connections:
IPSec-IKEv2: 10.112.18.105...%any IKEv2, dpddelay=300s
IPSec-IKEv2: local: [10.112.18.105] uses public key authentication
IPSec-IKEv2: cert: "C=US, O=Aurea, CN=cis-migration-vpn.aes.aurea.com"
IPSec-IKEv2: remote: uses public key authentication
IPSec-IKEv2: child: 10.112.0.0/16 === dynamic TUNNEL, dpdaction=clear
IPSec-IKEv2-EAP: 10.112.18.105...%any IKEv2, dpddelay=300s
IPSec-IKEv2-EAP: local: [10.112.18.105] uses public key authentication
IPSec-IKEv2-EAP: cert: "C=US, O=Aurea, CN=cis-migration-vpn.aes.aurea.com"
IPSec-IKEv2-EAP: remote: uses EAP_MSCHAPV2 authentication with EAP identity '%any'
IPSec-IKEv2-EAP: child: 10.112.0.0/16 === dynamic TUNNEL, dpdaction=clear
CiscoIPSec: 10.112.18.105...%any IKEv1, dpddelay=300s
CiscoIPSec: local: [10.112.18.105] uses public key authentication
CiscoIPSec: cert: "C=US, O=Aurea, CN=cis-migration-vpn.aes.aurea.com"
CiscoIPSec: remote: uses public key authentication
CiscoIPSec: remote: uses XAuth authentication: any
CiscoIPSec: child: 10.112.0.0/16 === dynamic TUNNEL, dpdaction=clear
Security Associations (1 up, 0 connecting):
IPSec-IKEv2-EAP[1]: ESTABLISHED 26 minutes ago, 10.112.18.105[10.112.18.105]...10.185.28.241[10.185.28.241]
IPSec-IKEv2-EAP[1]: Remote EAP identity: ryan
IPSec-IKEv2-EAP[1]: IKEv2 SPIs: 9b0fd7b8f81a8c6c_i 966e28db92550c47_r*, rekeying disabled
IPSec-IKEv2-EAP[1]: IKE proposal: AES_CBC_256/HMAC_SHA2_384_192/PRF_HMAC_SHA2_384/MODP_1024
[root@localhost strongswan]#
网络信息
[root@localhost strongswan]# cat /etc/sysctl.conf
# System default settings live in /usr/lib/sysctl.d/00-system.conf.
# To override those settings, enter new settings here, or in an /etc/sysctl.d/<name>.conf file
#
# For more information, see sysctl.conf(5) and sysctl.d(5).
# VPN
net.ipv4.ip_forward = 1
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.all.send_redirects = 0
[root@localhost strongswan]# ifconfig
ens192: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 10.112.18.105 netmask 255.255.254.0 broadcast 10.112.19.255
inet6 fe80::250:56ff:fe9a:b6c prefixlen 64 scopeid 0x20<link>
ether 00:50:56:9a:0b:6c txqueuelen 1000 (Ethernet)
RX packets 132983 bytes 33121546 (31.5 MiB)
RX errors 0 dropped 678 overruns 0 frame 0
TX packets 62082 bytes 11920649 (11.3 MiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
inet6 ::1 prefixlen 128 scopeid 0x10<host>
loop txqueuelen 0 (Local Loopback)
RX packets 20 bytes 2100 (2.0 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 20 bytes 2100 (2.0 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
virbr0: flags=4099<UP,BROADCAST,MULTICAST> mtu 1500
inet 192.168.122.1 netmask 255.255.255.0 broadcast 192.168.122.255
ether 52:54:00:a1:a6:70 txqueuelen 0 (Ethernet)
RX packets 0 bytes 0 (0.0 B)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 0 bytes 0 (0.0 B)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0
[root@localhost strongswan]# ip -4 a s
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
2: ens192: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
inet 10.112.18.105/23 brd 10.112.19.255 scope global ens192
valid_lft forever preferred_lft forever
3: virbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN
inet 192.168.122.1/24 brd 192.168.122.255 scope global virbr0
valid_lft forever preferred_lft forever
[root@localhost strongswan]# ip -4 r s t 0
default via 10.112.18.1 dev ens192 proto static metric 100
10.112.18.0/23 dev ens192 proto kernel scope link src 10.112.18.105 metric 100
192.168.122.0/24 dev virbr0 proto kernel scope link src 192.168.122.1
broadcast 10.112.18.0 dev ens192 table local proto kernel scope link src 10.112.18.105
local 10.112.18.105 dev ens192 table local proto kernel scope host src 10.112.18.105
broadcast 10.112.19.255 dev ens192 table local proto kernel scope link src 10.112.18.105
broadcast 127.0.0.0 dev lo table local proto kernel scope link src 127.0.0.1
local 127.0.0.0/8 dev lo table local proto kernel scope host src 127.0.0.1
local 127.0.0.1 dev lo table local proto kernel scope host src 127.0.0.1
broadcast 127.255.255.255 dev lo table local proto kernel scope link src 127.0.0.1
broadcast 192.168.122.0 dev virbr0 table local proto kernel scope link src 192.168.122.1
local 192.168.122.1 dev virbr0 table local proto kernel scope host src 192.168.122.1
broadcast 192.168.122.255 dev virbr0 table local proto kernel scope link src 192.168.122.1
[root@localhost strongswan]# ip route show table 220
10.42.42.1 via 10.112.18.1 dev ens192 proto static src 10.112.18.105
[root@localhost strongswan]# ip xfrm policy show
src 10.42.42.1/32 dst 10.112.0.0/16
dir fwd priority 2883 ptype main
tmpl src 10.185.28.241 dst 10.112.18.105
proto esp reqid 1 mode tunnel
src 10.42.42.1/32 dst 10.112.0.0/16
dir in priority 2883 ptype main
tmpl src 10.185.28.241 dst 10.112.18.105
proto esp reqid 1 mode tunnel
src 10.112.0.0/16 dst 10.42.42.1/32
dir out priority 2883 ptype main
tmpl src 10.112.18.105 dst 10.185.28.241
proto esp reqid 1 mode tunnel
src 0.0.0.0/0 dst 0.0.0.0/0
socket in priority 0 ptype main
src 0.0.0.0/0 dst 0.0.0.0/0
socket out priority 0 ptype main
src 0.0.0.0/0 dst 0.0.0.0/0
socket in priority 0 ptype main
src 0.0.0.0/0 dst 0.0.0.0/0
socket out priority 0 ptype main
src ::/0 dst ::/0
socket in priority 0 ptype main
src ::/0 dst ::/0
socket out priority 0 ptype main
src ::/0 dst ::/0
socket in priority 0 ptype main
src ::/0 dst ::/0
socket out priority 0 ptype main
[root@localhost strongswan]# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 10.112.18.1 0.0.0.0 UG 100 0 0 ens192
10.112.18.0 0.0.0.0 255.255.254.0 U 100 0 0 ens192
192.168.122.0 0.0.0.0 255.255.255.0 U 0 0 0 virbr0
[root@localhost strongswan]#
IP表
[root@localhost strongswan]# iptables-save
# Generated by iptables-save v1.4.21 on Fri Apr 15 18:03:58 2016
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [152:18472]
-A INPUT -p udp -m udp --dport 1701 -j ACCEPT
-A INPUT -p udp -m udp --dport 4500 -j ACCEPT
-A INPUT -p udp -m udp --dport 500 -j ACCEPT
-A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -p icmp -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -p tcp -m state --state NEW -m tcp --dport 22 -j ACCEPT
-A INPUT -p esp -j ACCEPT
-A INPUT -j REJECT --reject-with icmp-host-prohibited
-A FORWARD -p tcp -m tcp --tcp-flags SYN,RST SYN -j TCPMSS --clamp-mss-to-pmtu
-A FORWARD -j REJECT --reject-with icmp-host-prohibited
COMMIT
# Completed on Fri Apr 15 18:03:58 2016
# Generated by iptables-save v1.4.21 on Fri Apr 15 18:03:58 2016
*nat
:PREROUTING ACCEPT [866:126303]
:INPUT ACCEPT [9:2520]
:OUTPUT ACCEPT [14:1198]
:POSTROUTING ACCEPT [14:1198]
-A POSTROUTING -s 10.42.42.0/24 -o ens192 -m policy --dir out --pol ipsec -j ACCEPT
-A POSTROUTING -s 10.42.42.0/24 -o ens192 -j MASQUERADE
COMMIT
# Completed on Fri Apr 15 18:03:58 2016
[root@localhost strongswan]#
我最初在 Centos 7 中使用以下命令开始使用新的防火墙命令，但我遇到了完全相同的问题，希望回到旧的 iptables 会有所帮助，因为老实说，我对它了解得更多一些。以下是我当时运行的命令：
firewall-cmd --zone=dmz --permanent --add-rich-rule='rule protocol value="esp" accept' # ESP (the encrypted data packets)
firewall-cmd --zone=dmz --permanent --add-rich-rule='rule protocol value="ah" accept' # AH (authenticated headers)
firewall-cmd --zone=dmz --permanent --add-port=500/udp #IKE (security associations)
firewall-cmd --zone=dmz --permanent --add-port=4500/udp # IKE NAT Traversal (IPsec between natted devices)
firewall-cmd --permanent --add-service="ipsec"
firewall-cmd --zone=dmz --permanent --add-masquerade
firewall-cmd --set-default-zone=dmz
firewall-cmd --reload
firewall-cmd --list-all
你知道我做错了什么吗？为什么 ping 请求/响应会一直到达目标并返回 StrongSwan 服务器，但不会返回客户端？
答案1
好吧，我通过为我的 Strongswan 机器提供一个公共 IP 来实现这一点。这是唯一需要做的改变。所以现在我的网络看起来像这样：
[Windows 2012 Client ]------[External Nat]-----[VPN ]---------[Hidden network]
10.185.28.241 / 10.42.42.1 x.x.x.71 10.112.18.105 10.112.0.0/16
这就是所需的全部内容。我无需更改任何配置。我只需将指向 10.112.18.105 的 DNS 名称更改为 xxx71，其他内容保持不变。
据我所知，我的 Windows 客户端所在的 AWS 网络不知何故吞噬了返回的 ESP 数据包，因此在通过站点到站点 VPN 时从未收到服务器的响应。我根本不需要在 Strongswan 服务器上进行任何更改。我只需要通过公共 IP 而不是通过站点到站点 VPN 即可。