An IP (Internet Protocol) Query

[#1]

I've just got a new modem/router to replace my previous separate modem & router - its working fine .

However it provides my standard internet facing address, owned by Plusnet of 146.90.133.xxx

The router address is 192.168.1.1 - and the previous router happily accepted a default gateway address of 192.168.1.1.

However, the new modem/router decided it wanted to show a default gateway address of 172.16.11.165.

But 172.16.0.0 - 172.31.255.255 (172.16/12) are non-routable addresses - everything still works but I wonder what's going on?

[#2]

RTFM?

[#3]

There are three groups of IPv4 addresses that are reserved for private networks. 10.0.0.0 – 10.255.255.255, 172.16.0.0 – 172.31.255.255, 192.168.0.0 – 192.168.255.255. All three groups are considered non routable on the public internet. Within your local (private) LAN these are valid. When one of your devices accesses a public IP address the router translates the local address into your public 146.x.x.x address, and translates the responses back to the relevant local address. The technique is known as NAT addressing.

Most domestic router manufacturers use default Lan addresses in the range 192.168.x.x, and most people never change it. Your new router manufacturer simply chose a different and less common default.

On most routers you can change the internal addresses to whatever you prefer (but they should be within one of these ranges). I use 10.0.0.x.

Can you actually access the new router on 192.168.1.1? I suspect that the new router is at 172.11.16.165.

[#4]

The router is addressed as 192.168.1.1 to access the web page interface - so yes it works.

I've got DHCP restricted to handing out addresses in the range 192.168.1.3 - 192.168.1.100.

The LAN is defined as 192.168.1.1 with a subnet mask of 255.255.255.0

I tried a traceroute to 172.11.16.165 - and it made a valiant effort and partly succeeded!

From London it went to Sheffield, back to London then shot off to Kansas, USA and the last efforts I have it is still buzzing around about 10 different servers in Kansas...

So I don't think that belongs to me.

And I’m not gonna leave here ever, ever again, because I love you all, and – oh, Auntie Em – there’s no place like home!

I also tried a 192.168.xxx.xxx address - there's something wrong here.

~ $ traceroute 192.168.7.22
traceroute to 192.168.7.22 (192.168.7.22), 30 hops max, 60 byte packets
 1  router (192.168.1.1)  0.540 ms  0.644 ms  0.743 ms
 2  * * *
 3  * * *
 4  132.hiper04.sheff.dial.plus.net.uk (195.166.143.132)  7.501 ms 128.hiper04.sheff.dial.plus.net.uk (195.166.143.128)  7.602 ms  7.578 ms
 5 failed to get any further.

[#5]

Sorry my typo, I meant 172.16.11.165 not 172.11.16.165. The latter is outside the reserved block and is a valid address. (it belongs to lightspeed.irvnca.sbcglobal.net) and so should be routable. 

I have no idea why your router is giving out a default gateway of 172.16.11.165. If your LAN is 192.168.1.1 with a subnet mask of 255.255.255.0, then 172.16.11.165 should be unreachable, and any PC picking up the default gateway from the router should be unable to get anywhere.

Sorry I can't be of more help. I would reset the router and try again. Was it brand new?. If not possibly someone has set it up in the 172 range, and a reset doesn't change the default gateway.

[#6 · Accepted solution]

It was a brand new router, still in its sealed plastic wrappings.

Actually, I'm going to just ignore it, since it doesn't affect the working of the device at all.

[#7]

The gateway for your computers and other devices in your LAN is the router, on it's LAN IP address of 192.168.1.1.

The gateway for the router itself, where it sends your Internet traffic, which is the other end of the PPP connection, is the 172.16.11.165 address.

Also, as I mentioned in another recent thread, I don't think those 132.hiper04.sheff.dial.plus.net.uk reverse DNS entries actually indicate it's gone to Sheffield, I think it's more likely that the reverse DNS entries are years out of date.

[#8]

Thanks for that, @ejs - I think I understand - that 172.16.11.165 address sits on a Plusnet (or BT) switch or router.

Never really understood what PPP (Point-to-Point Protocol) actually meant - its a very common TLA

Seems the new modem/router provides slightly more stats.