[c-nsp] dot1Q trunk, not point-to-point

[Mike]

On 02/28/2012 06:09 AM, Victor Sudakov wrote:
> Colleagues,
>
> Is it required that a 802.1Q trunk is a point-to-point link between
> exactly two switches? What if I have several switches with trunk ports
> connected to a shared medium, should I expect problems?
>
> In my case, the shared medium would be a radio relay line acting as a
> dumb switch which can however handle 1522 byte frames.
>

Watch out - lots of wireless gear is outright treasonous and violates 
blindly many aspects of 802.1d which come back to bite you in the butt. 
This does not necessarily apply to 'real' equipment, such as licensed 
band alcatel, dragonwave, and the like, usually it's the cheaper stuff 
that's not on the market long that does it.

Some things I know about first hand include:


Not forwarding your traffic because it's not ARP or IP ether type (0x800 
and 0x806)

Having undeclared transmission rate limits that apply to 'broadcast' and 
'multicast' frames which is far below what it does for unicast, 
resulting in excessive loss, performance issues and outright protocol 
malfunction.

Allowing corrupt ethernet frames to be forwarded into the system (screws 
up the bridging tables since you can see effectively random mac addresses)

Using mac address translation to 'nat' mac addresses, and then using ip 
inspection to simulate bridging... until it sees a protocol it doesn't 
understand (non-ip), or runs out of translation entries, or is rebooted 
and doesn't see the opening frame and drops everything until the other 
side times out...

Reordering your packets, resulting in very extremly bad tcp peformance.

There's more. Think incompetence, but on an industrial scale and with 
dumb punk 19 year old kids given 'firmware coder' jobs for supposedly 
'carrier class' (w00t!) gear, and snazzy sales brochures that all sound 
great...until the network crashes because you did something that is 
legitimate (in a switched Ethernet environment, such as 802.1q trunking) 
that the gear never saw before ("It'll be fixed in the next revision!").

buyer beware.

Mike-