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

Owen DeLong owen at delong.com
Sat Mar 27 00:38:30 UTC 2010


On Mar 26, 2010, at 4:33 PM, Mark Foster wrote:

> 
>> "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?
> 
> If the network fabric you're on is important enough to cause you grief in the event of a STP event, you shouldn't be fielding 'dumb' switches.
> 
> Even the 'dumbest' switch I would ever place into user-space is fully managable, layer 2 with VLAN's and STP support.  That is, it's in a cabinet or TC and fed by infrastructure cabling, and the only folks who can get at it are the engineers and techs supporting the site.
> 
> The other side of things is that if DHCP times out once during STP negotiation, it rarely times out twice. Users whos machines are 'dynamically connected' often enough to have STP related glitches in their DHCP grab should know enough to hit 'repair' or run ipconfig /renew - or should be told to reboot :-)
> 
or reboot is problematic in many cases.  Many systems drop link-state during reboot for a long-enough period that the bridge-port restarts its spanning tree process, making results across reboots consistently bad.

>> 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?
> 
> There's plenty of desktop switches out there which are close to 'fully featured' - but obviously there's money involved. If your uplink switch (at the very least) supports STP then at least you can isolate the problem if the switch itself can't handle, but I wouldn't recommend this.
> 
With the additional advantage that the uplink switch link to the conference-room switch doesn't flap often enough to cause DHCP issues, but, will shut down the port if properly configured and the conference-room switch at least passes the BPDUs around the loop.

Owen





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