Re: [fw-wiz] null routes and VPN's



2008/5/20 Kerry Milestone <km4@xxxxxxxxxxxx>:
Hello,

is it a wise idea to put a default route on the inside (trusted) side of a
firewall with a high metric for when a VPN drops. Essentially, blackholing
all traffic until the VPN comes back and the default route is again the end
of the VPN?

Assuming there is a rule on the outside which allows only VPN traffic from
the other end (point to point and only traffic allowed through the VPN)
should both ends of the VPN have null routes for when its down ( for traffic
within the VLAN for this VPN)?

What would be the implementation side affects, something along the lines of
once the VPN is up its a matter of timeout on the routing protocol (say
OSPF) to propagate the default route? Should a modernish firewall do this
automagically anyway??

Cheers,
Kerry.



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I had a little trouble understanding your question, however i will say this.

There should be high weight black hole route for any given gateway, be
that gateway a default route, a lan interface, or a vpn, this is good
for many reasons.
1) it keeps down loop traffic, and reduces routing load in an already
compromised situation.
2) if used for a vpn it keeps you from spewing private traffic out an
unprotected or public link

i have only seen a few implementations where a vpn could use a black hole route
if your using an ipsec tunnel you dont have a real route to blackhole,
all you have is an interesting traffic filter
if your using a gre tunnel this might work
if your using mpls(or its siblings) this might work but im not sure if
its more trouble than its worth

just my 2cents



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-Lawrence
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