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Day: April 2, 2015

Creating a Bridge with a Span Port on OpenBSD 5.6

Published April 2, 2015

Since OpenBSD moved the bridge commands into ifconfig(8) I hadn’t been able to find quick info on creating a bridge(4). Presuming you’ve got some em(4) interfaces (for naming purposes) here’s all you need to do:

ifconfig em0 up
ifconfig em1 up
ifconfig em2 up
ifconfig bridge0 create
ifconfig bridge0 add em0
ifconfig bridge0 add em1
ifconfig bridge0 addspan em2
ifconfig bridge0 up

This will result in em0 and em1 bridged together, and a copy of all frames that it sees going out to em2 for monitoring.

After this, if you want it to come up every time you boot the machine, do this:

Create three files, /etc/hostname.em0, /etc/hostname.em1, and /etc/hostname.em2 all containing the single line:

up

Create one file, /etc/hostname.bridge0, containing the following lines:

add em0
add em1
addspan em2
up

Reboot the computer and netstart(8) will use these files to create the bridge for you.

One very important point to note if using this to troubleshoot 802.1x: this sort of bridge cannot be used to troubleshoot 802.1x because it does not pass LLDP frames, nor does it drop/raise the link, which switches commonly use as a trigger for initiating client authentication. For situations like this a tap such as the NetOptics TP-CU3 is much more useful.

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On-One Carbon Fatty Fork on 2012 Salsa Mukluk 2

Published April 2, 2015

 

Wanting to keep my fat bike around for a while longer I’ve been looking at cost effective ways to improve it. Last year this was new tubeless-ready wheels, and recently it’s been a great-value carbon fiber fork: the On-One Carbon Fatty Fork. At about US$250 shipped it’s considerably cheaper than many other options, and it’s geometry just happens to be close enough to that of the Mukluk’s original Enabler  fork. (468mm A-C and 45mm offset on the Enabler vs 470mm A-C and 55mm offset on the Fatty.) There is a 10mm difference in offset, which hopefully will not affect handling too much. Per various online bicycle geometry calculators there should be about 11mm less trail with the Fatty.

Trail calculations, for reference, per yojimg.net Bicycle Trail Calculator w/ 559mm BSD and 95mm tire width:

2012 Mukluk w/ Fatty: 79mm

2012 Mukluk w/ Enabler: 90mm

2015 Mukluk w/ Rigid Fork: 94mm

2015 Beargrease: 94mm

2015 Blackborow: 87mm

2015 Pugsley: 88mm

2015 Moonlander: 88mm

2015 Ice Cream Truck: 102mm

On-One Fatty w/ Carbon Fork: 94mm

2013 El Mariachi w/ Fox F29: 82mm

This ~11mm decrease in trail will likely make the front end feel much twitchier, bringing it just a smidge shortern than my favorite XC bike: the Salsa El Mariachi Ti which has 82mm of trail. If my understanding of trail is correct this’ll make the bike a bit twitchier and quicker to turn. Hopefully this won’t cause problems riding it at higher speeds, or keeping a line at slow speeds in the snow.

This fork is also set up with rear brake spacing — something that’s going away on newer fat bikes — which generally means that no special adapters are needed to get the brake caliper to align with the front hub. I did have to use two 1.5mm washers to space the caliper over for nice alignment with the rotor (photo), but this shouldn’t be a big deal. I’ll likely get some longer IS mounting bolts since the thread engagement isn’t quite enough to make me comfortable. Despite having a straight steerer the fork has a large crown intended to match the On-One Fatty frame. This results in a slightly awkward step below the headset (photo), but with the mostly-black bike I don’t think it looks too bad. I’m also not too keen on the orange logos, but in person I think it goes well enough with the sun-faded anodized red to not be a problem.

The originally intended purpose of this fork — front end weight reduction — seems to be successful. After replacement the weight has gone done 1.08 pounds, to 29.74 pounds (photo). The original steel Enabler fork, with crown race and star nut, was 1134g, while the On-One Carbon Fatty fork is 637g with crown race, compression plug / bung, and the steerer tube cut to length.

Now to wait for the trails to dry and see how it rides…

UPDATE: The decreased trail definitely makes the bike twitchier. It’s now a lot harder to ride no handed, but on single track it feels plenty lively and fun to ride. For now I think this is a good thing, although it’ll be curious to see how this pans out come winter.

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