[ih] Ethernet, was Why TCP?

[Brian E Carpenter]

On 02/09/2016 13:22, Larry Sheldon wrote:

...
>> The only parts of 'Ethernet' left are the packet format, and the host/network
>> interface standard. As always, the interface is left when the equipment on
>> either side has changed out of all recognition - check out the screw base on a
>> mains AC LED bulb...
> 
> Reminds me of a question I don't see discussed anywhere--do the 
> "Ethernet switches" (that replaced the "hubs" from my day in the sun) in 
> fact operate as "multi-port bridges" complete with Spanning Tree, BDUs, 
> and the other neat Radia Perlman* stuff?

Yes. But there are issues. For example, most of them are reluctant to relay
multicast packets (many people, including me, having horrible memories of
multicast or broadcast storms on early bridged networks). So they perform layer
violations - for example MLD snooping, where an L2 bridge listens to L3 Multicast
Listener Discovery packets (a form of ICMPv6 packet). I was bitten just a
couple of months ago by a "switch" with defective MLD snooping, such that it
dropped most link-local multicasts instead of relaying them to all ports.
I had to borrow a cheap old fashioned "switch" that actually behaved as a
Radia-style L2 bridge.

As I understand it, this sort of problem is the main reason Radia invented
TRILL.

    Brian