Concealing short disconnects

Andrew P. infofarmer at
Sun Feb 13 05:53:24 GMT 2005

Dan Nelson wrote:
> 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.

No, there's really nothing to be suspicious about :) The IP doesn't
change (well, in the process of IPCP it virtually does, first to and then back to the assigned one - but that doesn't
count, does it), the ppp process stays, but TCP/UDP streams are
somehow interrupted. Don't worry anyway. Disconnects happen in
5-6 in the morning, when all the users are sleeping and the only
one sleepless surfer is unlucky me, trying to seamlessly upgrade
self-made internet connection sharing box from 4.10 to 5.3.

BTW, if only anyone happens to know: I asked list before, but got
no reply. When ISP actually assigns new IP address, I occasionally
get double IPs on the tun0 interface (the old one and the new one
simultaneously). Everything's working fine, but the dyndns updater
can't recognize the IP change. Is there a way to fix this glitch/
feature? I've really manned and googled for it - without succes.

Best wishes,
Andrew P.

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