[LARTC] pointopoint flag

[LARTC] pointopoint flag

[mike stjohn]

how do you set the pointopoint flag using ip command?

is it an automatic setting when ip is configuring a ppp link | or am I
missing  something in the ip-cref.


thanks

msj


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Re: [LARTC] pointopoint flag

[Guy Van Den Bergh]

the pointtopoint flag is something typical for the medium used.
E.g. ethernet is by nature a broadcast medium and thus not pointtopoint.
PPP, as its name says,is a point to point protocol. So this is (or 
should be) not configurable, unless you are trying some weird setups.

Guy

mike stjohn wrote:

> how do you set the pointopoint flag using ip command?
> 
> is it an automatic setting when ip is configuring a ppp link | or am I
> missing  something in the ip-cref.
> 
> 
> thanks
> 
> msj
> 
> 
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> LARTC mailing list / LARTC@mailman.ds9a.nl
> http://mailman.ds9a.nl/mailman/listinfo/lartc HOWTO: http://ds9a.nl/2.4Routing/



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Re: [LARTC] pointopoint flag

[bert hubert]

On Thu, Mar 22, 2001 at 11:20:00PM +0100, Guy Van Den Bergh wrote:
> the pointtopoint flag is something typical for the medium used.
> E.g. ethernet is by nature a broadcast medium and thus not pointtopoint.
> PPP, as its name says,is a point to point protocol. So this is (or 
> should be) not configurable, unless you are trying some weird setups.

You CAN use Ethernet in a point-to-point configuration, by the way. Saves
some IP adresses.

Regards,

bert

-- 
http://www.PowerDNS.com      Versatile DNS Services  
Trilab                       The Technology People   
'SYN! .. SYN|ACK! .. ACK!' - the mating call of the internet

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Re: [LARTC] pointopoint flag

[Guy Van Den Bergh]

bert hubert wrote:

> 
> You CAN use Ethernet in a point-to-point configuration, by the way. Saves
> some IP adresses.
> 

How do you that? PPPoE (PPP over Ethernet)? This is more like ppp 
emulation over ethernet. And thus this introduces protocol overhead.

What do you mean by this? I'm puzzled.

Guy


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Re: [LARTC] pointopoint flag

[Guy Van Den Bergh]

bert hubert wrote:

> On Sun, Mar 25, 2001 at 08:07:48PM +0200, Guy Van Den Bergh wrote:
> 
> 
>>> You CAN use Ethernet in a point-to-point configuration, by the way. Saves
>>> some IP adresses.
>> 
>> How do you that? PPPoE (PPP over Ethernet)? This is more like ppp 
>> emulation over ethernet. And thus this introduces protocol overhead.
>> 
>> What do you mean by this? I'm puzzled.
> 
> 
> It's still ethernet. But instead of assigning a /30 with 4 IP addresses, you
> just route to your device. Not rocket science, just saves IP addresses.
> 
> Regards,
> 
> bert hubert


But you require the next hop to do proxy arp if you would like this to work!
And certainly this is not a point-to-point configuration of ethernet. If you route to your device instead of your nexthop
the kernel is going to send an arp request for de destination address, and if the destination is not on the lan,
some router on the lan has to do proxy arp on behalf of the destination. Otherwise your packets will be dropped.
The kernel still thinks the lan is a broadcast medium.

I believe this is a lot more complicated than "just routing to your device"!

Even if you have a crossconnect cable between two hosts or routers, the medium inbetween is still broadcast and not
point-to-point.

I know this discussion is going way too far into semantics, but as far as I know there is no such thing as point-to-point mode of ethernet.

Guy


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Re: [LARTC] pointopoint flag

[bert hubert]

On Sun, Mar 25, 2001 at 08:07:48PM +0200, Guy Van Den Bergh wrote:

> > You CAN use Ethernet in a point-to-point configuration, by the way. Saves
> > some IP adresses.
> 
> How do you that? PPPoE (PPP over Ethernet)? This is more like ppp 
> emulation over ethernet. And thus this introduces protocol overhead.
> 
> What do you mean by this? I'm puzzled.

It's still ethernet. But instead of assigning a /30 with 4 IP addresses, you
just route to your device. Not rocket science, just saves IP addresses.

Regards,

bert hubert

-- 
http://www.PowerDNS.com      Versatile DNS Services  
Trilab                       The Technology People   
'SYN! .. SYN|ACK! .. ACK!' - the mating call of the internet

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Re: [LARTC] pointopoint flag

[Gregory Maxwell]

On Sun, Mar 25, 2001 at 09:29:30PM +0200, Guy Van Den Bergh wrote:
> But you require the next hop to do proxy arp if you would like this to work!
> And certainly this is not a point-to-point configuration of ethernet. If you route to your device instead of your nexthop
> the kernel is going to send an arp request for de destination address, and if the destination is not on the lan,
> some router on the lan has to do proxy arp on behalf of the destination. Otherwise your packets will be dropped.
> The kernel still thinks the lan is a broadcast medium.
> 
> I believe this is a lot more complicated than "just routing to your device"!
> 
> Even if you have a crossconnect cable between two hosts or routers, the medium inbetween is still broadcast and not
> point-to-point.
> 
> I know this discussion is going way too far into semantics, but as far as I know there is no such thing as point-to-point mode of ethernet.

You can disable arp and set static arp entries. Do that, plus a crossover cable
and full-duplex, and I'd have a very hard time calling your ethernet
anything but point-to-point. :)

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Re: [LARTC] pointopoint flag

[Guy Van Den Bergh]

Gregory Maxwell wrote:

> On Sun, Mar 25, 2001 at 09:29:30PM +0200, Guy Van Den Bergh wrote:
> 
>> 
>> Even if you have a crossconnect cable between two hosts or routers, the medium inbetween is still broadcast and not
>> point-to-point.
>> 
>> I know this discussion is going way too far into semantics, but as far as I know there is no such thing as point-to-point mode of ethernet.
> 
> 
> You can disable arp and set static arp entries. Do that, plus a crossover cable
> and full-duplex, and I'd have a very hard time calling your ethernet
> anything but point-to-point. :)


The point was that it is a lot more complex than simply adding a route 
to the device instead of to the nexthop.
Let's remember that ethernet is by nature a broadcast medium and if you 
want it to behave like a point-to-point link you will have to be 
careful. Adding static arp entries has some drawbacks which you do not 
have on real point-to-point links.
In the end you are still trying to let a broadcast medium behave like a 
point-to-point link. Nothing more and nothing less.

Guy


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