netdev - Re: Link-local address handling for IPv4

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Date:	Tue, 22 Jun 2010 19:21:35 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	"Fischer, Anna" <anna.fischer@...com>
Cc:	netdev@...r.kernel.org
Subject: Re: Link-local address handling for IPv4

Le mardi 22 juin 2010 à 13:17 +0000, Fischer, Anna a écrit :
> Hi,
> 
> Does the Linux kernel network stack do any specific handling of 

> link-local address configuration and handling according to RFC 3927?

>  I know that there is user-level code like Zeroconf / Avahi and these

>  tools create ARP sockets directly on the specified network interfaces 

> in order to support link-local address handling. But if I do not 

> run any of these tools, does the kernel's ARP code take care of this, too?
> 

There is no RFC 3927 support in kernel, you need user space support (or
switch to DHCP ;) )

Note that ARP replies MUST also be broadcasted for this particular
169.254/16 network (RFC 3927, 2.5), you need a kernel patch too, this
was discussed 4 years ago on netdev, and nothing was decided/changed.

http://marc.info/?l=linux-netdev&m=114427223811197&w=2

BTW I believe that our forwarding path doesnt test source/destination
address not being part of 169.254/16 network, I am not sure it
is a real problem or not. A netfilter rule can fix it eventually.

7.  Router Considerations

   A router MUST NOT forward a packet with an IPv4 Link-Local source or
   destination address, irrespective of the router's default route
   configuration or routes obtained from dynamic routing protocols.

   A router which receives a packet with an IPv4 Link-Local source or
   destination address MUST NOT forward the packet.  This prevents
   forwarding of packets back onto the network segment from which they
   originated, or to any other segment.

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