Detect PPPoE vs. DHCP

Alex Tweedly alex at tweedly.net
Mon Nov 8 15:48:22 CST 2004


At 15:36 08/11/2004 -0500, Frank Engel wrote:

>Y?
>
>Actually, DHCP and PPPoE are completely different types of protocols; both 
>could theoretically be used together.  DHCP is basically a way to get an 
>IP address for yourself (along with info such as DNS addresses, default 
>router, etc.) over an existing IP network.  PPPoE is a way to bridge two 
>separate networks across a third network, without allowing that third 
>network access to either of the other two.  These are completely different 
>things, so I fail to understand what you are trying to determine here?

Let me make a guess .....

Although PPPoE can be used as a bridging medium, its most common usage 
nowadays is in consumer broadband connections, where the broadband 
connection itself is ethernet, but the ISP uses PPPoE to set up a PPP 
connection to the consumer - and hence can use their existing Radius (or 
other authentication system).

So for a consumer DSL connection, most are either

a. straight Ethernet - typically using DHCP to allocate an IP address
b. PPPoE

Can you distinguish between them ?

I know OSX is a bit different from other Unixes, so this may be wrong ....

If straight Ethernet + DHCP, I'd expect ifconfig to tell me about 
interfaces called en0, en1 or similar (sometimes e0, e1, etc)

If PPPoE, I'd expect to see those PLUS one or more called ppp0, ppp1, etc.

Not fully reliable, since you could have serial lines with ppp configured 
in addition to your ethernet interfaces - but it may help you get started 
on interpreting the ifconfig output.

-- Alex.


>On Nov 8, 2004, at 15:04, RGould8 at aol.com wrote:
>
>>Can anyone tell me if there's a way in Mac OS X to determine whether the user
>>is currently connected via DHCP vs. PPPoE?   Some sort of unix shell command
>>perhaps?   I've looked at the "ifconfig" command, and it spits back a lot if
>>interesting info, but nothing jumps out at me to denote "DHCP" vs. "PPPoE".
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>-----------------------------------------------------------
>Frank D. Engel, Jr.  <fde101 at fjrhome.net>
>
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>$
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