[Swan] feature request - route based (vti) vpn - ip address on tunnel interfaces

[Paul Wouters]

On Mon, 5 Sep 2016, Bruno Lopes de Souza Benchimol wrote:

>  I would like to request a new feature. Let me explain our scenario and what we trying to do libreswan:

>   We have on our Datacenter, a Palo Alto device that does handle as our VPN Server (IPsec) to multiple sites, and we use dynamic routing protocols (BGP and OSPF) -- currently BGP on the
> VPN side. We can make it properly work w/ other Palo Alto and Cisco devices.

>    The following links describes what we need to configure on devices:
> https://live.paloaltonetworks.com/twzvq79624/attachments/twzvq79624/documentation_tkb/525/1/How_to_Configure-Dynamic_Routing_over_IPSec_against_Cisco-vc.pdf

>    We have many sites that we are using Linux, and we choose Libreswan to be our VPN IPsec software. We first started using policy based VPN but we quickly found a problem: Dynamic
> Routing Protocols did not work as expected. The real trick is that routing protocols demand IP on tunnel interfaces to work properly and exchange adversites and routing protocol
> information. I was glad i found VTI support on the beta release, that really solves the issue, as i have a tunnel interface to route thru.
> 
>    I quickly found the problem. We need to have configured IP on the tunnel interface, and libreswan did not the manage that to do it properly. We could get the tunnel UP with properly
> local/remote ip address, but the interface did not have IP address (which is required to by routing protocols).
> 
>   What we need to do is configure one ip address, like 192.168.168.1/30 on site A (palo alto) and 192.168.168.2/30 on site B, and the local and remote tunnel which are the real ip
> address that we use to connect (that works good). To solve the issue i had to manually set the ip address by myself: # ip addr add 192.168.168.2/30 dev <vti-interface>

> So its fully working as i would like. I had to do a nasty workaround with systemd to get it working:
> 
> I had to add to ipsec.service ->
> 
> ExecStartPost=/opt/set-tunnel-ip.sh
> 
> # cat /opt/set-tunnel-ip.sh
> 
> #!/bin/bash
> sleep 5
> ip addr add 192.168.168.2/30 dev vti-pdp

>     Also, we need to modify to read {VTI_IP} from the configuration file. I would suggest another keyword:
> 
>     vti-ip=192.168.168.2/30

I think this is a good idea, and we should add support this. Although I would prefer to use:

 	leftvti-ip=192.168.168.2/30
 	rightvti-ip=192.168.168.1/30

While you can leave out one of these, it keeps the idea that you can use
the same config on both endpoints.

This would also translate in the updown scripts to MY_VTI_IP and PEER_VTI_IP

>     I believe the modifications should be fairly easy to implement. It should not be compatible with vti-shared as each tunnel must have its own unique ip. And by adding this feature it
> would make libreswan compatible with most VPN software (commercial) w/ Route based and Dynamic Routing Protocols.
> 
>      I would like to hear back from you guys if that's possible to do, and i believe it should not be much hard to implement.

I guess since this option would only be used with vti-shared=no, we
wouldn't need to delete the IP from the VTI device, as the entire
device will be removed from the system when the connection goes down.

Paul