Have you s…god dammit

<Rawn> I hate when you know for a fact that every person you work with has seen Office Space
<Rawn> and you can’t find your fucking stapler.
<Knehi> HAHAHA
<Rawn> Fuck you.
<Rawn> I have to go on a scavenger hunt for my stapler.  I can’t let anyone know it’s missing.
<Xir> stapler?
<Knehi> just walk around threatening to burn down the building, it will show up
<Rawn> <Xir> stapler?
<Rawn> Have you seen my…god dammit, I’d never hear the fucking end of it.
<Rawn> fuck it, i’ll use a hole punch and an elastic.
<Trolan> just swipe someone else’s
<Thayne> Just send out an email  Subject:  Stapler  Body:  Have you seen mine?
<Ayrahvon> You’ll never hear the end of it on IRC either, bad move. =P
<Rawn> I had to tell SOMEONE
<Rawn> I didn’t need this following me around irl
<Knehi> http://tinyurl.com/6j7e5h
* Trolan makes a note: Ask Ron about his stapler at Blizzcon.
[S+Z] Alicia (ottertothe@c-24-10-235-250.hsd1.ut.comcast.net) has joined channel #OnTheBounty
<Thayne> Hay Ali…Have you seen Ron’s stapler?
<Alicia> Is it red?
<Alicia> Because that would be awesome.
<Thayne> It is in my mind….
<Rawn> -_-
<Cal> I take Ron’s glare to mean that it is, in fact, red.
<Knehi> I take Ron’s glare to mean he still has a love of asian boys, but I take everything Ron does to mean that
<Trolan> so when he says red stapler, he means he wants something reddish, to bend over like a stapler is bent, and get banged hard.
<Trolan> got it.
<Alicia> He is going to poison all of your drinks.
<Rawn> This says a lot more about you people than it does about me.
<Rawn> And I would never waste a drink like that.
<Rawn> I’d just steal theirs.
<Alicia> haha
<Thayne> Shouldn’t you be looking for your stapler?
<Rawn> shouldn’t you be dying in a fire?
<Knehi> http://www.landoverbaptist.org/2008/august/olympicvolleyball.html
<Thayne> YOur vitriol will not help you find your stapler any quicker Sir.

These days, I just hard-code for job security.

Ultimately, it’s a lot easier to keep one’s job if you can convince your manager that it takes highly skilled, motivated, and incredibly rare individuals to log into a switch and change a port default or two.  I suspect this is also the reason why I read about cable runs taking nine-and-a-half weeks.  The whole stack of cards comes tumbling down the minute one of us admits that it should really only take 2-3 minutes, given the proper cable length and a path with minimal obstruction between distribution frames.

But I digress: http://etherealmind.com/2008/07/15/ethernet-autonegotiation-works-why-how-standard-should-be-set/

Some interesting notes there. I’ve actually been a fan of set-and-forget over the years, but never could explain why. It just seemed to fix a lot of errors, and ultimately that was what was important. Having had the chance to work with quite a few makes and models over the last two years or so, I’m getting more comfortable with the idea of auto-negotiation.

After all, auto-neg IS a standard, and the Gigabit Ethernet specification is pretty clear on the matter of its importance. If it doesn’t work between two devices, it’s ultimately not a design problem (as I preferred to think of it), but rather a driver incompatibility problem (one of your vendors is making garbage NIC’s). These days, my thinking is more along the lines of “if you have to disable a standard to make it work, you’ve got bigger problems than a few collisions.”

You can indeed force Gigabit Ethernet on a Cisco switch to “speed 1000,” but you will be unable to set the duplex; it will default to full and stay there. You’d think this was a good thing until you see the GigE spec excerpted in the article, where it states that GigE uses auto-neg to detect which end of the link will provide clocking. : )

Ex:

lab-sw-3(config)#int gi0/24

lab-sw-3(config-if)#speed 1000

lab-sw-3(config-if)#duplex full ! accepts this command without complaint; it defaulted to “full” in the first place

lab-sw-3(config-if)#duplex half

Gigabit port is restricted to full duplex ! gets upset if you try to set it to “half”

lab-sw-3(config-if)#duplex auto

Gigabit port is restricted to full duplex ! equally upset if you try to set it to “auto”

lab-sw-3(config-if)#

Little food for thought!

Getting to the root of the problem.

From the “Learn something new every day” department…this one could actually be relevent to my studies.*  It was certainly relevant to my job.

In building a three-switch lab to simulate one site’s access-layer and test out some link bundling, I was seeing that my access switch’s uplink had a cost to the root of 16.  This did not make sense.  The path went through a Gigabit uplink to the secondary root, which is connected to the primary root by way of a two-link EtherChannel (two 100Mbps links).  I was expecting a cost related to the sum of costs for one 1Gb and one 100Mb link (4 + 19 = 23).

In looking up the path costs to try and work backwards, I found the cost for 200 Mb is 12.  This combined with the cost of the Gig uplink would give me my 16 value, but where was the 200 Mb coming from?

The answer was that the EtherChannel’s virtual interface gets its own bandwidth, equal to the product of the individual link bandwidth and the number of links in the channel.  Doing a “show interface port-channel” would display a bandwidth of 200 Mbps, and STP uses this interface’s characteristics to derive its path costing:

Port-channel21 is up, line protocol is up (connected)
Hardware is EtherChannel, address is 0019.5669.5382 (bia 0019.5669.5382)
Description: *** HQD_CORE_01 ***
MTU 1500 bytes, BW 200000 Kbit, DLY 10 usec,
reliability 255/255, txload 1/255, rxload 2/255
Encapsulation ARPA, loopback not set
Full-duplex, 1000Mb/s, link type is auto, media type is unknown

This led me to wonder if this could be changed with the interface-level “bandwidth” command.  So for kicks, I changed the bandwidth of a random Gig link to 100 Mbps.  Here’s the before and after:

SW-1>sho span int gi2/0/9

Vlan             Role Sts Cost Prio.Nbr Type
—————- —- — ——— ——– ——————————–
VLAN0102         Desg FWD 4 128.61   P2p

Then the change…

SW-1(config)#int gi2/0/9
SW-1(config-if)#bandwidth 100000

Then the result:

SW-1>sho span int gi2/0/9

Vlan             Role Sts Cost Prio.Nbr Type
—————- —- — ——— ——– ——————————–
VLAN0102         Desg FWD 19 128.61   P2p

The cost to reach the root switch will be the primary determining factor in root-port selection, for any STP topology that involves uplinks to non-root switches. ** This can be influenced by the bandwidth of your links, which I knew already, but what I didn’t know was that the path-cost may inadvertently change with link-bundling or manual interface bandwidth configuration.

*Picture the following scenario: Given a topology consisting of three switches, make Fa0/1 on Switch-C the alternate port…but change nothing on its upstream switches; do not disable STP or employ FlexLinks; and do not manually change the port cost with any “spanning-tree” commands.

**If you’re merely running multiple uplinks from one switch to the root, given interfaces of equal bandwidth, your root bridge ID, path cost, and sender bridge ID will be equal.  The tie is broken based on port ID (2-tuple value consisting of Priority:Interface-Number).  Of course, if you’re doing that, you should really consider EtherChannel; additional path-redundancy and bandwidth, what’s not to love!