Re: ppp-2.4.2 released

["Pasi Kärkkäinen" <pasik@iki.fi>]

On Wed, Mar 03, 2004 at 07:13:08AM +0800, Bernard Blackham wrote:
> A while ago, Pasi wrote:
> > > > > > There's still the MTU bug (with MPPE) left..
> 
> > > What bug is that?
> 
> > I've sent couple of mails about this.. I'll explain it below.
> 
> > Now, the problem is, that the web-server is already sending packets which
> > have *right* size (the size client told), but the pptp-server rejects them
> > because of the ppp-interface MTU is too low (in the pptp server). 
> > 
> > pppd/ccp.c near line 1192:
> > 
> > mtu = netif_get_mtu(f->unit);
> > if (mtu)
> >     netif_set_mtu(f->unit, mtu - MPPE_PAD);
> > else
> >     newret = CONFREJ;
> > 
> > MPPE_PAD is defined as 4.
> > 
> > 
> > The pptp client sets the MTU to x (for example 1400), and the pptp server sets 
> > the MTU to x-4 (1396). This obviously happens only when using MPPE.
> > 
> > The pptp-client is not able to load the web page at all, because the client
> > doesn't receive any data from the web server! the pptp-server rejects the
> > incoming (http) packets.
> > 
> > This does not happen with all web sites.
> 
> Just a metoo message - I've been experiencing the exact same
> problems here. We have a poptop server serving over 100 concurrent
> connections and many users have noted that they weren't able to
> access the campus website.
> 
> The campus website is behind a Cisco load balancer, so this may be a
> suspect in breaking PMTU. Disabling the above lines of code also
> solved the problem here though and we've had few complaints since.
> 

Good to hear. 

Even if this is not a pppd bug, I think we should create some kind of
workaround (option?) for this?

Other ppp-servers don't seem to have this same problem.. so it makes you
feel that pppd is broken :)

-- Pasi Kärkkäinen
       
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