Re: won't talk to 2.4.0-test7 system

From: Gregory Maxwell (
Date: Sat Sep 02 2000 - 12:01:14 EST

On Sat, 2 Sep 2000, Matti Aarnio wrote:

> On Sat, Sep 02, 2000 at 04:12:04PM +0200, Elmer Joandi wrote:
> ....
> > There is another big problem like that...
> > tunnels actually do not work on todays real internet...
> > MTU 1500 is so much a standard that it starts killing tunnels.
> > MTU < 1500 is not a working solution today thanks to (mostly
> > linux based ? ) broken firewalls
> It is due to knee-jerk ICMP blocking settings at firewalls/routers.

Yes, this is indeed the primary cause. All of the Linux howtos for
firewalling appear to warn against this. Most of the time I've see this
happen it's been ACLs on a Cisco router. Checkpoint makes it harder to
make this mistake by having normally invisable 'ALLOW' rules for such
traffic (and DNS too).

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This archive was generated by hypermail 2b29 : Thu Sep 07 2000 - 21:00:13 EST