Linux
GRE 隧道之間的 Centos7 上未轉發數據包
如圖所示，我已經在 centos 機器和各個 centos 機器上的相應路由表之間配置了 GRE 隧道：
I dont have enough reputation to post imagesRouter1——–gre1———Transit-Router———gre2——–Router2
10.2.32.0/24–Router1–10.0.0.1—gre1—10.0.0.2–Transit-Router–11.0.0.2—gre2–11.0.0.1–Router2–10.4.32.0/24
我能夠從 Router-1 ping 到 gre1 隧道的另一端：
worker]# ping 10.0.0.2 PING 10.0.0.2 (10.0.0.2) 56(84) bytes of data. 64 bytes from 10.0.0.2: icmp_seq=1 ttl=64 time=1.43 ms 64 bytes from 10.0.0.2: icmp_seq=2 ttl=64 time=0.472 ms 64 bytes from 10.0.0.2: icmp_seq=3 ttl=64 time=0.291 ms 64 bytes from 10.0.0.2: icmp_seq=4 ttl=64 time=0.319 ms流量通過 GRE 隧道到達 Transit Router（由 tcpdump proto gre 驗證）
從 Router-2 ping 到 gre2 隧道另一端：
worker]# ping 11.0.0.2 PING 11.0.0.2 (11.0.0.2) 56(84) bytes of data. 64 bytes from 11.0.0.2: icmp_seq=1 ttl=64 time=1.10 ms 64 bytes from 11.0.0.2: icmp_seq=2 ttl=64 time=0.392 ms 64 bytes from 11.0.0.2: icmp_seq=3 ttl=64 time=0.369 ms 64 bytes from 11.0.0.2: icmp_seq=4 ttl=64 time=0.258 ms此流量也在隧道上流動
在中轉路由器上，我可以在添加路由條目後 ping 路由器 1 和路由器 2 的私有地址： 中轉路由器：
[root@vmc-centos conf]# ping 10.2.32.1 PING 10.2.32.1 (10.2.32.1) 56(84) bytes of data. 64 bytes from 10.2.32.1: icmp_seq=1 ttl=64 time=0.589 ms 64 bytes from 10.2.32.1: icmp_seq=2 ttl=64 time=0.380 ms 64 bytes from 10.2.32.1: icmp_seq=3 ttl=64 time=0.383 ms路由器 1：
worker]# tcpdump -i any proto gre -n 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 04:54:36.684864 IP 10.206.83.3 > 10.206.90.103: GREv0, length 88: IP 10.0.0.2 > 10.2.32.1: ICMP echo request, id 20445, seq 34, length 64 04:54:36.684951 IP 10.206.90.103 > 10.206.83.3: GREv0, length 88: IP 10.2.32.1 > 10.0.0.2: ICMP echo reply, id 20445, seq 34, length 64 04:54:37.684776 IP 10.206.83.3 > 10.206.90.103: GREv0, length 88: IP 10.0.0.2 > 10.2.32.1: ICMP echo request, id 20445, seq 35, length 64中轉路由器：
[root@vmc-centos conf]# ping 10.4.32.1 PING 10.4.32.1 (10.4.32.1) 56(84) bytes of data. 64 bytes from 10.4.32.1: icmp_seq=1 ttl=64 time=0.553 ms 64 bytes from 10.4.32.1: icmp_seq=2 ttl=64 time=0.325 ms 64 bytes from 10.4.32.1: icmp_seq=3 ttl=64 time=0.354 ms路由器 2：
worker]# sudo tcpdump -i any proto gre -n 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 04:56:57.549823 IP 10.206.83.3 > 10.206.86.199: GREv0, length 88: IP 11.0.0.2 > 10.4.32.1: ICMP echo request, id 20690, seq 24, length 64 04:56:57.549896 IP 10.206.86.199 > 10.206.83.3: GREv0, length 88: IP 10.4.32.1 > 11.0.0.2: ICMP echo reply, id 20690, seq 24, length 64但是現在當我嘗試從路由器 1 到達路由器 2（10.4.32.1）的專用網路時，數據包到達中轉路由器但沒有從那裡轉發到路由器 2：路由器 1：
worker]# ping 10.4.32.1 PING 10.4.32.1 (10.4.32.1) 56(84) bytes of data.中轉路由器：
[root@vmc-centos conf]# tcpdump -i any proto gre -n tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on any, link-type LINUX_SLL (Linux cooked), capture size 262144 bytes 04:59:06.382024 IP 10.206.90.103 > 10.206.83.3: GREv0, length 88: IP 10.0.0.1 > 10.4.32.1: ICMP echo request, id 36131, seq 40, length 64 04:59:07.382007 IP 10.206.90.103 > 10.206.83.3: GREv0, length 88: IP 10.0.0.1 > 10.4.32.1: ICMP echo request, id 36131, seq 41, length 64路由器 2：
[root@wdc-10-206-86-199 worker]# sudo tcpdump -i any proto gre -n 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在所有機器上啟用路由轉發：
[root@vmc-centos conf]# sudo sysctl -p net.ipv4.ip_forward = 1中轉路由器上的 iptables：
[root@vmc-centos ~]# iptables -L Chain INPUT (policy ACCEPT) target prot opt source destination ACCEPT gre -- anywhere anywhere ACCEPT gre -- anywhere anywhere Chain FORWARD (policy DROP) target prot opt source destination DOCKER-USER all -- anywhere anywhere DOCKER-ISOLATION-STAGE-1 all -- anywhere anywhere ACCEPT all -- anywhere anywhere ctstate RELATED,ESTABLISHED DOCKER all -- anywhere anywhere ACCEPT all -- anywhere anywhere ACCEPT all -- anywhere anywhere Chain OUTPUT (policy ACCEPT) target prot opt source destination ACCEPT gre -- anywhere anywhere Chain DOCKER (1 references) target prot opt source destination Chain DOCKER-ISOLATION-STAGE-1 (1 references) target prot opt source destination DOCKER-ISOLATION-STAGE-2 all -- anywhere anywhere RETURN all -- anywhere anywhere Chain DOCKER-ISOLATION-STAGE-2 (1 references) target prot opt source destination DROP all -- anywhere anywhere RETURN all -- anywhere anywhere Chain DOCKER-USER (1 references) target prot opt source destination RETURN all -- anywhere anywhere注意：我之前已經嘗試過，數據包正在到達另一個專用網路。現在我嘗試另一種設置，我缺少一些配置。
Docker 守護程序似乎正在轉發機器上執行。預設情況下，為了隔離不同網橋和宿主機上的容器，Docker 會在 iptables 中的轉發鏈上安裝一個預設的 DROP 策略。Docker 守護程序中有一個設置不這樣做。在 .iptables 中將 iptables 設置為 false
/etc/docker/daemon.json。請參閱Docker 和 iptables如果您將預設策略更改為接受，那將起作用。
iptables --policy FORWARD ACCEPT但是，當您（或 docker 的軟體包升級，或重新啟動）重新啟動 Docker 守護程序時，如果您沒有更改 docker 守護程序的設置，預設策略將再次更改為 DROP。