How Skype uses the network [was: News item: Blackberry services down worldwide]

["Patrick W. Gilmore" <patrick () ianai net>]

On Oct 13, 2011, at 7:26 PM, Matthew Kaufman wrote:
> On 10/13/11 3:30 PM, Patrick W. Gilmore wrote:
> > In fact, Skype, just as a for instance, is worse on hotel wifi as launching the app on a laptop makes you a middle 
> > node for some conversations. 
>
> Per the Skype IT administrator guide, a Skype node will not become a supernode unless it has a public IP address and 
> meets the memory, bandwidth, and uptime requirements. It will not become a relay node unless it has a public IP 
> address and is directly reachable from the Internet.
>
> It is very unlikely that launching the Skype app on a laptop on hotel wi-fi would meet these requirements.

In the last 5 seconds, without touching Skype or having any active voice or chat sessions open, my computer has had 
communication with 14 IP addresses.  Here is a sample of some:

        TiggerAir-i7-2:~ patrick$ host 94.193.99.152
        152.99.193.94.in-addr.arpa domain name pointer 94-193-99-152.zone7.bethere.co.uk.
        TiggerAir-i7-2:~ patrick$ host 78.90.137.244
        Host 244.137.90.78.in-addr.arpa. not found: 3(NXDOMAIN)
        TiggerAir-i7-2:~ patrick$ host 175.129.63.150
        150.63.129.175.in-addr.arpa domain name pointer KD175129063150.ppp-bb.dion.ne.jp.
        TiggerAir-i7-2:~ patrick$ host 218.190.29.244
        Host 244.29.190.218.in-addr.arpa. not found: 3(NXDOMAIN)
        TiggerAir-i7-2:~ patrick$ host 128.2.238.215
        215.238.2.128.in-addr.arpa domain name pointer ETC-NALZAYER.ETC.CMU.EDU.
        TiggerAir-i7-2:~ patrick$ host 212.187.172.66
        Host 66.172.187.212.in-addr.arpa. not found: 3(NXDOMAIN)

Those do not look like Skype servers.  I guess it is possible everyone in my contact list is somehow pinging me, but 
that seems a little bit silly.

My IP address is 172.30.19.19, hopefully I do not have to explain that this is not a "public IP address".  I have been 
online a few minutes, so unless their uptime requirements are about the same as a regular phone call, it is too short.  
I will admit, I have plenty of bandwidth available, though.

In short, while they can claim my laptop is not being used as a supernode or relay, Skype is still randomly talking to 
a slew of IP addresses.  Anyone know what Skype is doing?


> > Does Skype on $HANDHELD have the same property? 
> Not as far as I know, for the obvious reason that handheld devices have network connections that are suboptimal for 
> this.

The above happens to my laptop when I am on 3G / EDGE, even when I have a 10-net address.  In fact, one of the first 
things I do on 3G is kill Skype because it noticeably increases my network performance.

I haven't checked on my iPhone 'cause I don't have things like tcpdump & little snitch.

-- 
TTFN,
patrick