Re: [lwip-users] IP6 address autoconfig problem when using hub

[Sylvain Rochet]

Hi,

On Sun, Dec 09, 2012 at 10:53:58AM +0100, Simon Goldschmidt wrote:
> Zach Smith wrote:
> 
> > I am having a problem when I connect my IPv6 device running lwip to 
> > a hub instead of a switch. [..] Since a hub forwards all packets 
> > received onto all ports it is echoing my devices neighbor discovery 
> > messages back.
> 
> I haven't had the chance to test lwIP on a hub, yet (we only have 
> switches, all hubs were thrown away a long time ago...). However, if 
> your hub really sends back all your frames, I guess IPv6 autoconfig 
> will not be the only protocol having problems.

Added to that, a hub being half duplex by design is not supposed to 
bounce back packets, because it can only have one RX port at a time 
while all other should be TX ports (or there is a collision).

So, a hub DOES NOT forwards all packets received onto all ports, a hub 
DOES forwards all packets received onto all ports EXCEPT the sender 
port, if this is not the case, this is because there is an Ethernet loop 
somewhere or a faulty device that should be fixed/replaced.

Anyway, a switch without a populated MAC forwarding table is working 
like a hub and bounce packets to all ports except the sender' one.

Sylvain

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