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wifi interface wlan0 shows about 10-15% more traffic than VPN ppp0

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#1 ubunut

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Posted 10 March 2012 - 08:27 PM

I tried doing a search for vpn but it wont let me search under four characters so i will be so bold as to start a new topic.
I've been exploring the wonderful world of linux for a while now and since lately i got myself a vpn connection from ipredator which i use at all times when connected to the internet

I've been doing some scripting to have all relevant processes killed and the network disconnect in case the vpn goes down, i guess i'm just a bit paranoid. But all that works just fine.
Now i've been monitioring traffic on both ppp0 and wlan0 interfaces with this nifty little tool called ifstat.
What i notice is that at any time i am connected and traffic goes through the ppp0 interface i get about 10-15% more through my wlan0 interface. I have no clue where to ask about this and can't find the keywords to google the relevant information.
So, if anyone can help me out here? is it normal to have that much more traffic on the wi-fi than what goes actually through the vpn connection? Is it to do with the fact that the data's being encrypted or something? Anything to make me wiser about it or point me in the direction where i can find more info about this specific situation would be greatly appreciated.

I put a small portion of the output of ifstat here on pastebin : http://pastebin.com/9NEa8Zar

Go easy on me, i know a bit or two about computers but this is completely new to me.

Also, i can't seem to find anything about firewall rules to have a single program/process blocked from using anything but the ppp0 interface, all i can find is allow ip-ranges and open-close ports, anything for dummies on that subject would be most welcome as well
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#2 hybrid

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Posted 10 March 2012 - 08:45 PM

Am I right in thinking that the VPN is ppp0, and that the traffic then exits through wlan0, which is the actual physical interface you're using?

If so, I think this is probably just due to normal network overhead.

Any transmission of any data over the network involves overhead -- you have to not just send the information, but other metadata too. With Internet Protocol (IP), for example, data is split up into individual packets, with a maximum of 1500 bytes of data each. But, each packet also needs, for example, a source and destination IP address, and information that can be used to work out how to put the packets back in the right order at the other end! That extra data adds up to an additional 60 bytes to that 1500, for each packet, an extra 4%.

There is a 'stack' of different protocols and software that we use to have the communication successfully get from one place to another. In this case, your VPN protocol, TCP, IP and 802.11g/n or whatever, all have to work together to get the message delivered from source to destination. Each of these layers adds another little bit of overhead, with its own header and trailer information -- the metadata I talked about with IP.

So if all your traffic is getting VPNed at ppp0, then passing through wlan0, the additional 10-15% of data transfer is likely just that -- the overheads involved in taking the encrypted VPN packets, and repackaging them, at each layer, to allow them to have everything they need to get to their destination and be interpreted properly at the other end!

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