Re: Auto MDI/MDI-X + conference rooms + bored == loop

[Owen DeLong <owen () delong com>]

Switches that support STP?

There are switches that have STP protection such that they are
portfast until they see an inbound BPDU and then revert to
spanning tree on that port (it blocks, listens, learns, then
forwards if appropriate).

The only draw-back to such a configuration I am aware of is
that you have the (very small) overhead of all such ports
sending BPDUs.

Owen

On Mar 26, 2010, at 3:09 PM, Chuck Anderson wrote:

> Anyone have suggestions on Ethernet LAN loop-prevention?  With the 
> advent of Auto MDI/MDI-X ports on switches, it seems way too easy to 
> accidentally or maliciously create loops between network jacks.  We 
> have bored or inattentive people plugging in patch cords between 
> adjacent network jacks.  STP for loop-prevention isn't working so well 
> for us.
>
> STP "edge" or "portfast" or "faststart" modes are required for 
> end-station ports (with normal STP, DHCP often times out after 30+ 
> seconds it takes to go into Forwarding state).  Since the "edge" STP 
> mode goes into Forwarding state immediately, there is a period when 
> loops will form, causing havok with upstream gear until STP blocks the 
> port (if it ever does see below).
>
> "Desktop" switches.  You know, those 4 or 5 port Gigabit Ethernet 
> switches.  Apparently, many of them don't do any kind of STP at all.  
> Recommendations on ones that do STP?
>
> RSTP: is it any better than traditional STP in regards to "edge" ports 
> and blocking before a loop gets out of hand?  Or perhaps blocking for 
> 5-10 seconds before going into Forwarding state, hopefully preventing 
> loops before they happen but also allowing DHCP clients to get an 
> address without timeouts?  Recommendations on "Desktop" switches that 
> do RSTP?
>
> Thanks for your suggestions/discussion.
>
> -- 
> - Chuck (354 Days until IPv4 depletion: http://ipv4depletion.com/)