svn commit: r304436 - in head: . sys/netinet

[Bruce Simpson]

On 20/08/16 16:42, Bruce Simpson wrote:
> On 20/08/16 16:27, Ryan Stone wrote:
>> Can you send a broadcast packet through an L3 tunnel?  I thought that a
>> L2 tunnel was required.
>
> Yes. This is perfectly legal and necessary for forwarding of IPv4
> broadcasts to work. (it is Internet Protocol after all, not
> Infernal-ethernet-extension Protocol. ;-))

For completeness: This does not hold true for L2 in L2, the most obvious 
example being Metro Ethernet VMAN style service. There, Ethernet is the 
transport (link layer), as well as the payload. That's a concrete 
example of the kind of L2 'tunnel' you may be referring to.

Sometimes, specific Ethernet [broad|multi]cast destinations -- notably 
L2 control protocols, e.g. RSTP within the customer VLAN, may need to be 
tunnelled (Provider-Backbone-Bridges (PBB) style).

Alternatively, the L2 destination MAC may be rewritten for that specific 
address, to avoid the destination being interpreted by routers in the 
Metro Ethernet core. It can be considered a crude form of Ethernet NAT, 
but it's common practice.

But, for IP, forwarding IPv4 directed broadcast packets over a 
non-broadcast link is completely legal (and required for normal operation).