DDWRT 正在运行 VPN 客户端守护程序（接口 tun1），所有流量（有几个例外）都通过该接口路由。
第一个例外是端口 12600 上的流量应通过 进行路由vlan2，这是常规的非 VPN 互联网连接。这允许我在外出时通过 SSH 连接到我的路由器。
# Create table 202 via the Gateway Ip on the Interface VLAN2
ip route add default via $(nvram get wan_gateway) dev vlan2 table 202
# Apply the rule on table 202 to packages marked with 22
ip rule add fwmark 22 table 202
# Tag with 22 every output package on port 12600 not coming from any machine in the local network
iptables -t mangle -I OUTPUT -p tcp --sport 12600 -d ! 192.168.1.0/24 -j MARK --set-mark 22
这就像魅力一样有效:-)
现在，第二个问题是将端口 16001 转发到我的 Raspberry PI（本地 IP 192.168.1.132），并通过该vlan2接口路由该流量，而不是tun1.
转发部分正在工作：
iptables -t nat -I PREROUTING -p tcp --dport 12601 -j DNAT --to 192.168.`.132:12601
iptables -I FORWARD -i vlan2 -d 192.168.1.132 -p tcp --dport 12601 -j ACCEPT
此时，如果我停用路由器上的 OpenVPN 守护进程，则通过 SSH 进入 RPI 即可正常工作。问题是，当守护程序处于活动状态时，程序包会vlan2按预期通过接口到达 RPI，RPI 发回响应，并通过 进行路由tun1，从而使 SSH 无法进行。
我尝试添加规则：
iptables -t mangle -I OUTPUT -p tcp -s 192.168.1.132 -j MARK --set-mark 22
但这并没有奏效。我看到没有软件包被标记为该规则。
有人指的是rp_filter，但是我的都设置为0（这肯定是DD-WRT的默认值，因为我没有修改它）：
root@DD-WRT:~# sysctl -a | grep \\.rp_filter
net.ipv4.conf.all.rp_filter = 0
net.ipv4.conf.br0.rp_filter = 0
net.ipv4.conf.default.rp_filter = 0
net.ipv4.conf.eth0.rp_filter = 0
net.ipv4.conf.eth1.rp_filter = 0
net.ipv4.conf.eth2.rp_filter = 0
net.ipv4.conf.imq0.rp_filter = 0
net.ipv4.conf.imq1.rp_filter = 0
net.ipv4.conf.lo.rp_filter = 0
net.ipv4.conf.teql0.rp_filter = 0
net.ipv4.conf.tun1.rp_filter = 0
net.ipv4.conf.vlan1.rp_filter = 0
net.ipv4.conf.vlan2.rp_filter = 0
这些是我的 iptables：
root@DD-WRT:~# iptables -vnL -t nat
Chain PREROUTING (policy ACCEPT 183 packets, 30508 bytes)
pkts bytes target prot opt in out source destination
4 256 DNAT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:12601 to:192.168.1.132:12601
53 3644 DNAT udp -- br0 * 0.0.0.0/0 0.0.0.0/0 udp dpt:53 to:192.168.1.1
0 0 DNAT tcp -- br0 * 0.0.0.0/0 0.0.0.0/0 tcp dpt:53 to:192.168.1.1
0 0 DROP tcp -- * * 192.168.1.1 192.168.1.1 tcp dpt:443
0 0 ACCEPT tcp -- * * 192.168.1.0/24 192.168.1.1 tcp dpt:443
3 180 DNAT tcp -- * * 0.0.0.0/0 !73.93.100.100 tcp dpt:80 to:192.168.1.1:8118
0 0 DNAT tcp -- * * 0.0.0.0/0 73.93.100.100 tcp dpt:8080 to:192.168.1.1:443
0 0 DNAT tcp -- * * 0.0.0.0/0 73.93.100.100 tcp dpt:12600 to:192.168.1.1:12600
0 0 DNAT icmp -- * * 0.0.0.0/0 73.93.100.100 to:192.168.1.1
126 21928 TRIGGER 0 -- * * 0.0.0.0/0 73.93.100.100 TRIGGER type:dnat match:0 relate:0
Chain INPUT (policy ACCEPT 11131 packets, 732K bytes)
pkts bytes target prot opt in out source destination
Chain OUTPUT (policy ACCEPT 60 packets, 6022 bytes)
pkts bytes target prot opt in out source destination
Chain POSTROUTING (policy ACCEPT 23 packets, 4522 bytes)
pkts bytes target prot opt in out source destination
92 9920 MASQUERADE 0 -- * tun1 0.0.0.0/0 0.0.0.0/0
2 120 SNAT 0 -- * vlan2 192.168.1.0/24 0.0.0.0/0 to:73.93.100.100
root@DD-WRT:~# iptables -vnL -t mangle
Chain PREROUTING (policy ACCEPT 1787 packets, 398K bytes)
pkts bytes target prot opt in out source destination
1787 398K FILTER_IN 0 -- * * 0.0.0.0/0 0.0.0.0/0
385 101K VPN_IN 0 -- tun+ * 0.0.0.0/0 0.0.0.0/0
Chain INPUT (policy ACCEPT 529K packets, 462M bytes)
pkts bytes target prot opt in out source destination
53 7298 IMQ 0 -- tun+ * 0.0.0.0/0 0.0.0.0/0 IMQ: todev 0
559 161K IMQ 0 -- vlan2 * 0.0.0.0/0 0.0.0.0/0 IMQ: todev 0
293 35826 IMQ 0 -- !vlan2 * 0.0.0.0/0 0.0.0.0/0 IMQ: todev 1
Chain FORWARD (policy ACCEPT 487K packets, 318M bytes)
pkts bytes target prot opt in out source destination
332 94003 IMQ 0 -- tun+ * 0.0.0.0/0 0.0.0.0/0 IMQ: todev 0
98 5984 TCPMSS tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp flags:0x06/0x02 TCPMSS clamp to PMTU
39 6701 IMQ 0 -- vlan2 * 0.0.0.0/0 0.0.0.0/0 IMQ: todev 0
918 204K IMQ 0 -- !vlan2 !vlan2 0.0.0.0/0 0.0.0.0/0 IMQ: todev 1
Chain OUTPUT (policy ACCEPT 823 packets, 196K bytes)
pkts bytes target prot opt in out source destination
0 0 MARK tcp -- * * 0.0.0.0/0 !192.168.1.0/24 tcp spt:12600 MARK set 0x16
21 16378 IMQ tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp spt:8118 IMQ: todev 0
0 0 MARK tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:12601 MARK set 0x16
Chain POSTROUTING (policy ACCEPT 928K packets, 531M bytes)
pkts bytes target prot opt in out source destination
525 89419 VPN_OUT 0 -- * tun+ 0.0.0.0/0 0.0.0.0/0
1827 412K FILTER_OUT 0 -- * * 0.0.0.0/0 0.0.0.0/0
0 0 DSCP 0 -- * * 0.0.0.0/0 0.0.0.0/0 DSCP match !0x00 DSCP set 0x00
Chain FILTER_IN (1 references)
pkts bytes target prot opt in out source destination
1787 398K CONNMARK 0 -- * * 0.0.0.0/0 0.0.0.0/0 CONNMARK restore
1413 324K SVQOS_SVCS 0 -- * * 0.0.0.0/0 0.0.0.0/0 mark match 0x0/0x7ffc00
1787 398K CONNMARK 0 -- * * 0.0.0.0/0 0.0.0.0/0 CONNMARK save
1787 398K RETURN 0 -- * * 0.0.0.0/0 0.0.0.0/0
Chain FILTER_OUT (1 references)
pkts bytes target prot opt in out source destination
1827 412K CONNMARK 0 -- * * 0.0.0.0/0 0.0.0.0/0 CONNMARK restore
1488 328K SVQOS_SVCS 0 -- * * 0.0.0.0/0 0.0.0.0/0 mark match 0x0/0x7ffc00
1827 412K VPN_DSCP 0 -- * * 0.0.0.0/0 0.0.0.0/0
1827 412K CONNMARK 0 -- * * 0.0.0.0/0 0.0.0.0/0 CONNMARK save
1827 412K RETURN 0 -- * * 0.0.0.0/0 0.0.0.0/0
Chain SVQOS_SVCS (2 references)
pkts bytes target prot opt in out source destination
2901 653K RETURN 0 -- * * 0.0.0.0/0 0.0.0.0/0
Chain VPN_DSCP (1 references)
pkts bytes target prot opt in out source destination
0 0 MARK 0 -- * * 0.0.0.0/0 0.0.0.0/0 DSCP match 0x0a MARK xset 0x19000/0x7ffc00
0 0 MARK 0 -- * * 0.0.0.0/0 0.0.0.0/0 DSCP match 0x01 MARK xset 0x2800/0x7ffc00
126 32463 MARK 0 -- * * 0.0.0.0/0 0.0.0.0/0 DSCP match 0x02 MARK xset 0x5000/0x7ffc00
0 0 MARK 0 -- * * 0.0.0.0/0 0.0.0.0/0 DSCP match 0x03 MARK xset 0x7800/0x7ffc00
77 20422 MARK 0 -- * * 0.0.0.0/0 0.0.0.0/0 DSCP match 0x04 MARK xset 0xa000/0x7ffc00
313 73735 DSCP 0 -- * * 0.0.0.0/0 0.0.0.0/0 DSCP match !0x00 DSCP set 0x00
1827 412K RETURN 0 -- * * 0.0.0.0/0 0.0.0.0/0
Chain VPN_IN (1 references)
pkts bytes target prot opt in out source destination
385 101K CONNMARK 0 -- * * 0.0.0.0/0 0.0.0.0/0 CONNMARK save
Chain VPN_OUT (1 references)
pkts bytes target prot opt in out source destination
root@DD-WRT:~# iptables -vnL -t filter
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
95 20753 ACCEPT 0 -- tun1 * 0.0.0.0/0 0.0.0.0/0
864 291K ACCEPT 0 -- * * 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED
0 0 ACCEPT udp -- vlan2 * 0.0.0.0/0 0.0.0.0/0 udp spt:67 dpt:68
0 0 ACCEPT udp -- vlan2 * 0.0.0.0/0 0.0.0.0/0 udp dpt:520
0 0 DROP udp -- br0 * 0.0.0.0/0 0.0.0.0/0 udp dpt:520
0 0 ACCEPT udp -- * * 0.0.0.0/0 0.0.0.0/0 udp dpt:520
146 12000 ACCEPT 0 -- br0 * 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT tcp -- * * 0.0.0.0/0 192.168.1.1 tcp dpt:443
0 0 logbrute tcp -- vlan2 * 0.0.0.0/0 192.168.1.1 tcp dpt:12600
0 0 ACCEPT tcp -- vlan2 * 0.0.0.0/0 192.168.1.1 tcp dpt:12600
0 0 DROP icmp -- vlan2 * 0.0.0.0/0 0.0.0.0/0
0 0 DROP 2 -- * * 0.0.0.0/0 0.0.0.0/0
4 293 ACCEPT 0 -- lo * 0.0.0.0/0 0.0.0.0/0 state NEW
0 0 ACCEPT 0 -- br0 * 0.0.0.0/0 0.0.0.0/0 state NEW
162 27477 DROP 0 -- * * 0.0.0.0/0 0.0.0.0/0
Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
731 143K ACCEPT 0 -- * tun1 0.0.0.0/0 0.0.0.0/0
544 189K ACCEPT 0 -- tun1 * 0.0.0.0/0 0.0.0.0/0
11 688 ACCEPT tcp -- vlan2 * 0.0.0.0/0 192.168.1.132 tcp dpt:12601
86 12596 ACCEPT 0 -- * * 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED
158 37906 lan2wan 0 -- * * 0.0.0.0/0 0.0.0.0/0
156 37786 ACCEPT 0 -- br0 br0 0.0.0.0/0 0.0.0.0/0
2 120 ACCEPT 0 -- br0 vlan2 0.0.0.0/0 0.0.0.0/0
0 0 DROP tcp -- * vlan2 0.0.0.0/0 0.0.0.0/0 tcp dpt:1723
0 0 DROP udp -- * vlan2 0.0.0.0/0 0.0.0.0/0 udp dpt:1701
0 0 DROP udp -- * vlan2 0.0.0.0/0 0.0.0.0/0 udp dpt:500
0 0 TRIGGER 0 -- vlan2 br0 0.0.0.0/0 0.0.0.0/0 TRIGGER type:in match:0 relate:0
0 0 trigger_out 0 -- br0 * 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT 0 -- br0 * 0.0.0.0/0 0.0.0.0/0 state NEW
0 0 DROP 0 -- * * 0.0.0.0/0 0.0.0.0/0
我tcpdump可以看到端口 12601 上流向 RPI 的入站流量正在通过，vlan2但出站流量路由于tun1：
root@DD-WRT:~# tcpdump -n -i vlan2 port 12601
listening on vlan2, link-type EN10MB (Ethernet), capture size 65535 bytes
20:49:19.983896 IP 208.54.5.222.47184 > 73.93.100.100.12601: Flags [S], seq 1024682508, win 65535, options [mss 1380,nop,wscale 5,nop,nop,TS val 336905559 ecr 0,sackOK,eol], length 0
20:49:21.055561 IP 208.54.5.222.47184 > 73.93.100.100.12601: Flags [S], seq 1024682508, win 65535, options [mss 1380,nop,wscale 5,nop,nop,TS val 336906559 ecr 0,sackOK,eol], length 0
20:49:22.092159 IP 208.54.5.222.47184 > 73.93.100.100.12601: Flags [S], seq 1024682508, win 65535, options [mss 1380,nop,wscale 5,nop,nop,TS val 336907559 ecr 0,sackOK,eol], length 0
20:49:23.055189 IP 208.54.5.222.47184 > 73.93.100.100.12601: Flags [S], seq 1024682508, win 65535, options [mss 1380,nop,wscale 5,nop,nop,TS val 336908559 ecr 0,sackOK,eol], length 0
root@DD-WRT:~# tcpdump -n -i tun1 port 12601
listening on tun1, link-type RAW (Raw IP), capture size 65535 bytes
20:49:37.052293 IP 73.93.100.100.12601 > 208.54.5.222.47184: Flags [S.], seq 3536123446, ack 1024682509, win 28960, options [mss 1460,sackOK,TS val 2958399 ecr 336905559,nop,wscale 7], length 0
20:49:38.062308 IP 73.93.100.100.12601 > 208.54.5.222.59028: Flags [S.], seq 2196420762, ack 1024682509, win 28960, options [mss 1460,sackOK,TS val 2958500 ecr 336916559,nop,wscale 7], length 0
20:49:38.995709 IP 73.93.100.100.12601 > 208.54.5.222.41591: Flags [S.], seq 4130650631, ack 1024682509, win 28960, options [mss 1460,sackOK,TS val 2958593 ecr 336924559,nop,wscale 7], length 0
3 packets captured
3 packets received by filter
0 packets dropped by kernel
答案1
成功了。看起来 iptables 发生了变化，即使ip route flush cache在 DD-WRT 刷新之前不会发生；我所说的刷新是指重新启动所有主要服务，更改某些设置并单击后会发生什么Apply Changes。
作为参考，我希望能够从外部网络通过 SSH 访问我的 Raspberry Pi。 RPI 连接到作为客户端运行 OpenVPN 的 DD-WRT 路由器。 DD-WRT 需要将端口 12601 (SSH) 转发到 RPI，并避免通过 VPN 接口tun1（默认）发送响应包，因为响应包是通过 Internet 网关传入的vlan2。
这是我的防火墙脚本的样子：
# Create a rule to skip the VPN
echo 0 > /proc/sys/net/ipv4/conf/all/rp_filter
iptables -t mangle -F PREROUTING
ip route add default table 200 via $(nvram get wan_gateway)
ip rule add fwmark 1 table 200
ip route flush cache
## SSH to RPI (port 12601)
# First the port forwarding part
iptables -t nat -I PREROUTING -p tcp --dport 12601 -j DNAT --to 192.168.4.132:12601
iptables -I FORWARD -i vlan2 -d 192.168.1.132 -p tcp --dport 12601 -j ACCEPT
# Now mark packages from RPI and source port 12601 with tag 1. The rule above will direct packages marked with 1 through the wan gateway
iptables -t mangle -I PREROUTING -i br0 -p tcp -s 192.168.1.132 --sport 12601 -j MARK --set-mark 1