[124243] in North American Network Operators' Group
Re: Auto MDI/MDI-X + conference rooms + bored == loop
daemon@ATHENA.MIT.EDU (Owen DeLong)
Fri Mar 26 20:48:05 2010
From: Owen DeLong <owen@delong.com>
In-Reply-To: <Pine.LNX.4.64.1003271227330.15072@skyhawk.blakjak.net>
Date: Fri, 26 Mar 2010 17:38:30 -0700
To: Mark Foster <blakjak@blakjak.net>
Cc: Chuck Anderson <cra@WPI.EDU>, nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Mar 26, 2010, at 4:33 PM, Mark Foster wrote:
>=20
>> "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?
>=20
> 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.
>=20
> 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.
>=20
> 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 :-)
>=20
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?
>=20
> 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.
>=20
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
