Re: [gentoo-user] GRE link state detection

[Mick <michaelkintzios@gmail.com>]

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On Thursday 05 Sep 2013 15:49:55 thegeezer wrote:
> Howdy all,
> i was wondering if anyone has any idea if there is a means by which i
> can detect GRE link state ?
> 
> what i have is two sites each with two very unstable internet links
> in order to vpn between them i have ipsec tunnels linking each side
> twice (four ipsec tunnels in total)

I am not sure why you need 4 tunnels, you could just use 1 tunnel as a gateway 
to gateway setup, but I assume that your particular network topology satisfies 
your requirements.


> i then have 4x GRE tunnels over the top of those in order that i have a
> secured routable VPN
> this gives me net.vpn0 net.vpn1 net.vpn2 and net.vpn3
> finally i run BIRD over the top which works very well, and synchronises
> routing tables between the two sites, and allows for me to do such fun as
> # /etc/init.d/net.vpn0 stop
> and watch all traffic automagically cut over to another link.
> 
> so far so awesome.
> 
> however, as i said the internet links are very unstable, and sometimes
> just blackhole. so what i was hoping to do is just enable keepalives on
> the gre tunnel.  which sadly seems to be cisco only.

I'm no Cisco expert, but I thought that the keepalives are disabled when you 
use IPSec, because IPSec had Dead Peer Detection for this purpose?


> can anyone suggest a way of detecting if the GRE is not fully connected ?
> BIRD only fails over if the net.vpn0 device is down (ifconfig up/down)
> and for the life of me i cannot find how to detect if a GRE tunnel is
> 'connected', it seems to just blindly send packets to the remote IP.
> is my only choice to use L2TP instead ?

Set your IKE lifetime to something like 86400 sec and your SA lifetime at 
something like 3600, with dpd enabled and it should (hopefully) work.  L2TP is 
not needed.

-- 
Regards,
Mick

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