If you are working as a consultant, it is sometimes not easy to get proper network access when you are using your customer's network. The easiest way to solve this problem is to connect via your mobile phone. But, the 3G network is not always the fastest and it would be nice to use the normal network for certain tasks and the 3G network for others.
The problem in my case was that I wanted to connect to Github but, SSH
traffic was blocked on the network where I was working. So what to do?
I quick mail to the Jayway tech mailing list, lets me know that in Linux
there is a
route command, that can solve this problem. (Un)Fortunately
I am not using Linux on my development machine, but it turns out there
route(8) command in BSD too, with slightly different syntax.
Find the IP-address of the host I wish to connect to
# Find the IP-address of the host I wish to connect to $ nslookup github.com Server: 188.8.131.52 Address: 184.108.40.206#53 Non-authoritative answer: Name: github.com Address: 220.127.116.11
Find out the gateway of the interface of the cell phone
# Find out the gateway of the interface of the cell phone $ ifconfig lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384 inet 127.0.0.1 netmask 0xff000000 inet6 ::1 prefixlen 128 inet6 fe80::1%lo0 prefixlen 64 scopeid 0x1 ... vmnet8: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500 ether 00:50:56:c0:00:08 inet 192.168.105.1 netmask 0xffffff00 broadcast 192.168.105.255 en3: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500 ether 06:1e:64:00:34:1a inet6 fe80::41e:64ff:fe00:341a%en3 prefixlen 64 scopeid 0xa inet 172.20.10.3 netmask 0xfffffff0 broadcast 172.20.10.15 media: 10baseT/UTP status: active
In my case the interface I want to use is the last one, en3 with inet 172.20.10.3 but if you are unsure, you can open the network preference pane and look it up there.
Now I need to find out what the gateway for this interface is. I can
do this with
# Show the routing table $ netstat -r Routing tables Internet: Destination Gateway Flags Refs Use Netif Expire default 10.67.10.254 UGSc 10 0 en1 default 172.20.10.1 UGScI 0 0 en3 10.67.10/24 link#5 UCS 3 0 en1 10.67.10.88 localhost UHS 1 811 lo0 10.67.10.254 0:14:4f:69:da:13 UHLWI 10 41 en1 661 10.67.10.255 link#5 UHLWbI 1 78 en1 127 localhost UCS 0 0 lo0 ... Internet6: Destination Gateway Flags Netif Expire localhost localhost UH lo0 fe80::%lo0 localhost Uc lo0 localhost link#1 UHL lo0 ...
Close to the top we find the entry for our interface en3.
default 172.20.10.1 UGScI 0 0 en3
Now we have the ip to the gateway that we wanted. So now the last step is to make sure that access to github.com is routed via this gateway.
#route command -host destination gateway $ sudo route add -host 18.104.22.168 172.20.10.1 add host 22.214.171.124: gateway 172.20.10.1
That's it, I'm done. To make sure the routing is changed I check the
routing table with
netstat -r again, to make sure the new entry is in it.
$ netstat -r Routing tables Internet: Destination Gateway Flags Refs Use Netif Expire default 10.67.10.254 UGSc 30 0 en1 default 172.20.10.1 UGScI 0 0 en3 10.67.10/24 link#5 UCS 4 0 en1 10.67.10.88 localhost UHS 0 973 lo0 10.67.10.254 0:14:4f:69:da:13 UHLWI 27 11 en1 708 10.67.10.255 ff:ff:ff:ff:ff:ff UHLWbI 1 14 en1 127 localhost UCS 0 0 lo0 ... github.com 172.20.10.1 UGHS 0 43 en3 Internet6: Destination Gateway Flags Netif Expire localhost localhost UH lo0 fe80::%lo0 localhost Uc lo0 localhost link#1 UHL lo0 fe80::%en0 link#4 UC en0
Sure enough, there it is,
github.com. Finally I can now
and everything works :).
If I want to remove the entry, when I'm working elsewhere, I do that with
$ sudo route delete -host 126.96.36.199 172.20.10.1