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Cisco ASA Dynamic VPN

Posted on 2014-03-18
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Last Modified: 2014-08-29
Hi,

I am wondering if anybody has come up up with a cleaver solution to this problem?

Scenario:
1. We have a main HUB with ~35 VPNs to different customers.
2. We have one customer who have a Cisco ASA behind an ADSL router with dynamic IP so we must configure it with a dynamic VPN cryptomap in our HUB.
3. VPN is IPSec Site to Site
4. Tunnel work just fine.

The problem is rather that the tunnel is not setup automatically, it requires "interesting traffic" to pass before the tunnel is established.
Is there any way to make it connect automatically?

I tried to configure the customer ASA with "Originate Only" but then I received errors in the HUB where the customer ASA was trying to setup a tunnel for <CustomerASA Local IP 192.168.0.11> and <Main HUB Public IP> which did not match any crypto map.

I also tried to set up an IP SLA but that did not generate the sufficient traffic. Though, issuing a ping from the customer ASA to our office did get the tunnel going ("ping inside 192.168.0.1" for example).

Would be nice to see if anybody have found a solution to this :-)

Cheers!
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Question by:MarcusSjogren
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Expert Comment

by:asavener
ID: 39950636
My solution was to set up an automated polling engine at the remote site, such as What's Up Gold or similar running as a service on an internal server.

A side benefit is that it can sent alert E-mails.  (Best if they have an internal mail server.  External mail servers are often unavailable due to the same outage causing the VPN to fail.)
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Author Comment

by:MarcusSjogren
ID: 39952945
Thanks for your suggestion Asavener, but we currently don't have any server there who can do the polling for us.
Therefore I tried to do it via IP SLA but that did not seem to generate interesting traffic to setup the tunnel.
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Expert Comment

by:asavener
ID: 39953083
Does the SLA entry show as up when the VPN is connected and down when the VPN is disconnected?

If I recall correctly, the IP SLA does not allow you to specify a source IP address.  You might need to edit the VPN access list to include ICMP, source outside IP, destination inside IP at VPN endpoint.
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by:MarcusSjogren
ID: 40138184
asavener:

Hmm - I was farily sure I responded to your answer, but obviously not.

Anyhow - yes, it does show up and down and ICMP is allowed. However - my understanding is that the Cisco ASA cannot generate "Interesting traffic" on its own, it has to be generated from the local LAN. I dont understand why but that seems to be the case.

I dont think that what I want to do is possible.
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Author Comment

by:MarcusSjogren
ID: 40138185
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Expert Comment

by:asavener
ID: 40139147
The ASA can definitely produce interesting traffic, but the source address will be the outside interface.  So you have to edit the VPN access list and ONLY include traffic with the correct source and destination addresses.  (For example, if you include the outside interface address and the peer address, the VPN will attempt to tunnel its own traffic.)
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Author Comment

by:MarcusSjogren
ID: 40139156
I have indeed tried to create interesting traffic by using IP SLA with correct source IP etc. but that does not seem to be interesting to put inside the VPN tunnel anyway.
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Expert Comment

by:asavener
ID: 40139165
Did you create a matching traffic ACL on the other end of the VPN?
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Author Comment

by:MarcusSjogren
ID: 40139175
Are you referring to crypto map acl or normal acl?

The crypto map is the full subnets:

Site A:
192.168.0.0/24 (inside) -> 192.168.1.0/24 (Site B)

Site B:
192.168.1.0/24 (inside) -> 192.168.0.0/24 (Site A)
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Accepted Solution

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asavener earned 1000 total points
ID: 40139243
OK.  You will need to add a range that matches the possible outside interface addresses of the ASA with the dynamic address.

For example, if the ASA with the dynamic address is Site B:

Site A:
192.168.0.0/24 -> 192.168.1.0/24
192.168.0.0/24->  208.1.1.0/24

Site B:
192.168.1.0/24 -> 192.168.0.0/24
208.1.1.0/24 -> 192.168.0.0/24


Then you set up your IP SLA monitor on Site B, so that it periodically pings a 192.168.0.0/24 address.
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Author Comment

by:MarcusSjogren
ID: 40139250
Hi,

OK - that sounds strange, since I have configured the IP SLA to use a specific source address. But I will see if I can manage to make some tests some day :)
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Expert Comment

by:asavener
ID: 40139338
My experience is that the IP SLA on the ASA is a little squirrely.
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Author Closing Comment

by:MarcusSjogren
ID: 40292432
The resolution marked as an accepted solution works OK, but the IP SLA still does not work as expected as interesting traffic does not seem to be generated by the ASA.
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