Rerouting VPN Traffic from Cisco AnyConnect
I am connecting to a Client's network via the Cisco AnyConnect VPN. I'm quite impressed with the security of the client, it allows the VPN administrator to have alot of control over how the client can connect.
One problem I was facing though is that I couldn't connect to the internet while I am connected to the client's VPN. The VPN changed my default gateway to route everything through the VPN. Now since I don't want my internet traffic going through the VPN I have to change my default gateway back to my own router (192.168.2.1 in my case), I do that with the command (I'm on a Mac):
sudo route change default 192.168.2.1
Now I need to add a special routing rule to allow me to connect to the servers I need to get to on the VPN server (you may or may not need to do this):
sudo route add 192.168.123.0 10.1.1.1
10.1.1.1 would be the VPN gateway, and
192.168.123.0 is the network the servers I need to connect to are on.
After doing all this you would think everything would be setup for me to work, but I still couldn't connect to the internet! When I tried to ping google this is what I get:
ping: sendto: Permission denied Request timeout for icmp_seq 0
It turns out after some digging I discovered that the Cisco AnyConnect VPN client was adding rules to my Mac's local firewall (
ipfw). You can list the firewall rules using:
sudo ipfw -a list
One of the lines in there was:
01200 667 136583 deny ip from any to any
Which basically blocks all internet traffic except those that were specified explicitly specified by the VPN client. You can delete the rule using this command:
sudo ipfw delete 01200
01200 is the first set of numbers on the line. You may want to add in some additional protection back as well, you can do that as you see fit. The key point of this blog entry though is to point out that the firewall was manipulated by the Cisco AnyConnect client, and in order to customize how it works you need to alter the firewall settings each time you connect.
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# The Cisco AnyConnect VPN Client is often configured on the server to block
# all other Internet traffic. So you can be on the VPN <b>OR</b> you can have
# access to Google, etc.
# This script will fix that problem by repairing your routing table and
# firewall after you connect.
# The script does require admin (super user) access. If you are prompted for
# a password at the start of the script, just enter your normal Mac login
# The only thing you should need to configure is the vpn_ip_network.
# Mine is 10.x.x.x so I just specify '10' but you could be more specific
# and use something like '172.16'
vpn_ip_network = '10'
lines = subprocess.Popen(cmd if isinstance(cmd, list) else cmd.split(' '), stdout=subprocess.PIPE, stderr=subprocess.STDOUT).communicate()
lines = lines.decode('utf-8')
return [line.strip() for line in lines.strip().split('\n')]
sys.stdout.write("Mac Account Login ")
good_firewall_ids = set([line.partition(' ') for line in output_of('sudo ipfw -a list')])
gateway = None
for line in output_of('route get default'):
name, delim, value = line.partition(':')
if name == 'gateway':
gateway = value.strip()
p = subprocess.Popen(['/Applications/Cisco/Cisco AnyConnect VPN Client.app/Contents/MacOS/Cisco AnyConnect VPN Client'], stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
was_disconnected = False
line = p.stdout.readline()
if line == ' or p.poll():
line = line.decode('utf-8')
if 'Disconnected' in line:
sys.stdout.write('Waiting for you to enter your VPN password in the VPN client...\n')
was_disconnected = True
if 'Connected' in line:
subprocess.Popen(['sudo','route','-nv','add','-net',vpn_ip_network,'-interface','utun0'], stdout=subprocess.PIPE, stderr=subprocess.STDOUT).wait()
subprocess.Popen(['sudo','route','change','default',gateway], stdout=subprocess.PIPE, stderr=subprocess.STDOUT).wait()
unfriendly_firewall_ids = list(set([line.partition(' ') for line in output_of('sudo ipfw -a list')])-good_firewall_ids)
extra = '
subprocess.Popen('sudo ipfw delete'.split(' ') + unfriendly_firewall_ids, stdout=subprocess.PIPE, stderr=subprocess.STDOUT).wait()
sys.stdout.write("VPN connection established, routing table repaired and %d unfriendly firewall rules removed!\n" % len(unfriendly_firewall_ids))
sys.stdout.write("VPN connection established and routing table repaired!\n")
sys.stdout.write('VPN was already connected. Extra VPN client closed automatically.\n')
sys.stdout.write('VPN was already connected. Please close the extra VPN client.\n')
sys.stdout.write("Couldn't get gateway. :-(\n")