[124242] in North American Network Operators' Group
Re: Auto MDI/MDI-X + conference rooms + bored == loop
daemon@ATHENA.MIT.EDU (Anton Kapela)
Fri Mar 26 20:20:05 2010
From: Anton Kapela <tkapela@gmail.com>
In-Reply-To: <20100326234832.GB13305@angus.ind.WPI.EDU>
Date: Fri, 26 Mar 2010 20:19:28 -0400
To: Chuck Anderson <cra@WPI.EDU>
Cc: nanog@nanog.org
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Mar 26, 2010, at 7:48 PM, Chuck Anderson wrote:
> If you have 2 network jacks next to each other in a conference room,=20=
> do they each get configured as a separate "user"?
Indeed, most of the buildings have a 'community room' like that -- but =
all the deployed ports (unless ordered differently) will get =
incrementing-vlan assignments, so indeed, they'd be different vlans back =
to l3 core.=20
> What happens if a=20
> user connects them together?
Nothing, basically, as the network from edge port towards IP edge is (or =
should be) loop-free. The router will hear DHCP req's on 2x ints, but =
the client will (should) pick the first-heard response. Depending on the =
DHCP client implementation, it may wedge/break, but I haven't =
encountered one in testing. For higher-availability from edge towards IP =
core, LACP/PAGP provides link-independence, and UDLD/802 OAM provide =
something of a decent safety-net for breakage detection in metro-spans =
over other providers/resellers.=20
> What happens if a user plugs a desktop=20
> switch into one of them, then connects two ports on *that* switch=20
> together?
In my example config, bcast or mcast over 100 pps shuts the port that's =
receiving the bcast or mcast's down -- but, that's a configurable =
action. It could discard them, police them, or just report a syslog/trap =
to the NMS... Of course, this is all switch-vendor specific, etc.
> Would this work in a collapsed L2/L3 core (no agg, no L3 at edge)?
Oh, indeed -- and is. The UTOPIA network (http://www.utopianet.org/) in =
SLC, Utah, is doing basically this for it's ISP-reseller tiers. ISP's =
get customers on vlans or Q-stacked vlans, and do what they will with =
it. The ISP's I've talked with have tended to use Juni ERX for this, but =
there's nothing stopping one from using IOS, or another vendor that can =
do this trick. It just implies something to consider in the layer2 =
transport network (support for man l2 addrs in cam, QinQ, etc) at =
design-time.
> When doing 1:1 VLAN:Port mapping, can you do more than 4096=20
> VLANs/ports? Or are you doing QinQ?
Indeed -- q-stacking enables this. In most cases, I don't backhaul more =
than a few hundred vlans per building -- if it's over 200 to 250 =
ports/jacks, I generally drop local 3550/3560/3750 or cpu-based boxes =
on-site, routing towards the metro edge/backbone.
> Cool, but I'm not sure this will work in my non-Cisco campus=20
> environment with 10,000 edge ports.
Ahh; a pickle. C and J do indeed enable this in many of the popular =
boxes, which is great. That's not to say other vendors don't have =
something like it--the concept is perhaps the most valuable bit to =
discuss here, imho; the vendor-particulars are less important.
-Tk
