On Sat, 01 Jun 2013 11:00:47 +0100 Anthony Anson tony.anson@girolle.co.uk allegedly wrote:
On 31/05/13 15:23, mick wrote:
This address will vary depending on your method of connection. At home you may have a fixed IP address from your ISP. It is more likely though that you will have a dynamic address allocated from a pool by the ISP. When out and about your public address will be that allocated by the network provider at the time (and may be interfered with by varying levels of proxies).
My ISP tells me (by proxy) that it hasn't allocated me an IP address, and that it will be tacked-on by whatever host/dongle etc I'm connecting through, which is why I have to have a 'roaming connection'.
Anthony
At home (or wherever you use your dongle) your public IP address will be that allocated by your ISP. This address may be drawn from a small pool of proxy addresses on the ISP's network and will be used to mask your real local IP address which will also have been allocated by your ISP (you say you are using a 3G dongle, not wifi to a local router at home.) When out and about and using a wifi network from another provider (in your case you said that you were using a wifi network in a cafe in Norwich) you will get a public IP address from /that/ provider (and also a real local IP address.)
Prove it to youself with Stuart's suggested test. use curl to get your IP address when connected over a free wifi. Then disconnect and reconnect using your 3G dongle. Now check again. You will have a different IP public address.
You could go further and open a terminal to the shell and check your local IP address in each case (which will have been allocated from a DHCP pool by the provider you are using). Type "ifconfig -a" and look for the second line in each interface description starting "inet addr:" Ignore the local loopback (127.0.0.1) and you will see an address on the form 10.n.n.n or 192.n.n.n or 172.n.n.n. Most typically from a 3G network the address will be of the form 10.n.n.n because the telcos use that large address range on their internal dynamic networks. More typically on a wifi network in a cafe you will see 192.168.n.n because the local wifi router will be configured to hand out addresses from that much smaller pool.
HTH
Mick
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