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A couple of questions re PPPoE

FIXED
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Newbie
Posts: 2
Fixes: 1
Registered: ‎25-09-2020

A couple of questions re PPPoE

Hi

For historical (some would say hysterical) reasons, I am still happily using my Openreach modem for FTTC Fibre Extra with my own (Synology) router in (mesh) Wi-Fi router mode (also several ethernet connections via internal switches).

Writing-up some notes for posterity to document my setup, I see that the ethernet WAN side of the router has been allocated a private network 10 address and the PPPoE tunnel virtual interface has a private 172.16 endpoint address.

Meanwhile, my public IP is in the 87.x.x.x range - as revealed by What Is My IP.

From my internal LAN, traceroute gets to the public IP in one hop and shows a .dyn.plus.net hostname.

Traceroute gets to an Internet IP via the router at 192.168.1.1, the PPPoE tunnel endpoint, and then onwards from

137.hiper04.sheff.dial.plus.net.uk

On the router, the routing table shows the PPPoE-WAN interface as the default gateway, as expected.

 

Q1 - Where is the tunnel actually to? the DSLAM, the local exchange, a Plusnet router?

 

Q2 - Is there a one-to-one mapping between the PPPoE endpoint address and the public IP, even though it is in a private address range, or else is there some kind of NAT going on out there?

 

Intrigued as I know double-NAT can cause problems.

 

Realise at my advanced age that you can think you know a lot but there is always something new to learn - keeps me going since I started with mini-UNIX and PDP11s in the 1970s!

 

1 REPLY 1
Highlighted
Newbie
Posts: 2
Fixes: 1
Registered: ‎25-09-2020

Re: A couple of questions re PPPoE

Fix

Ok

 

i have now realised that I was missing something that now seems obvious - the source IP address in the IP packets encapsulated by PPPoE - which of course is indeed the public IP address I see from what is my IP.

So the tunnel goes all the way to the ISP and packets already have the correct source IP when extracted. No NAT needed.

Today I have learned to THINK more.

ADMIN please delete, lock or archive.

Thanks