Concealing short disconnects

Dan Nelson dnelson at
Sat Feb 12 07:41:40 GMT 2005

In the last episode (Feb 12), Andrew P. said:
> Dan Nelson wrote:
> >In the last episode (Feb 12), Andrew P. said:
> >>I have a few machines behind my FreeBSD box. The box connects to
> >>ISP via ppp (PPPoE protocol). It's all working very nicely, but the
> >>ISP is a pain - it disconnects every 24 hours. I can reconnect in
> >>just a moment - so the diconnect is usually less than a second
> >>long, but many applications, like ICQ/MSN and games "feel" the
> >>disconnect. The matter is that these applications can handle fairly
> >>large packet loss (e.g. Counter-Strike can cope with at least
> >>15-second long 100% packet loss), but AFAIK it's in the nature of
> >>the TCP/UDP that a disconnect is a disconnect.
> >>
> >>As I know that FreeBSD is full of magic, is there any way to
> >>conceal these reconnects as short moments of 100% packet loss? I am
> >>ashamed to know very little about protocols' technicalities, but
> >>I'll look into any sources you advise.
> >
> >Check to see if your IP number changes when you reconnect.  If it
> >does, there's nothing you really can do; the remote system you were
> >talking to knew you only by your old IP, and those packets coming to
> >them from this other IP are unrelated.
> It changes only once in about a week. Let's say it doesn't change
> at all. What then?

I'm still suspicious :)  The two most common causes for connection
resets are IP address changes and NAT resets.  /usr/sbin/ppp keeps its
NAT table across disconnects as long as the process itself stays
running, so I don't think that's the cause.  If you have root access to
a remote system, try running tcpdump on it and your local machine while
running something like top over ssh, and watch what happens when your
connection drops and reconnects.

	Dan Nelson
	dnelson at

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