Sunday, May 30, 2010

Demystifying 10G modules

I don't currently have any 10G gear in networks I manage, but I've been occasionally looking at 10G products so that when I need them, I'll have a clue about what the heck is going on with that market segment.

Looking through old NANOG presentations, I found a pdf from a presentation about 10G fiber pluggable modules.

This gives a great overview of what's out there and where the market is apparently going in terms of hardware.

Wednesday, May 26, 2010

Some handy commands for the F5 LTM

Some useful commands:
  • To show data on existing connections, use "b conn show" for a condensed list, or "b conn show all" for more information about the connections.
  • "bigpipe interface 1.1 media show" to show the speed/duplex of an interface - in this case, int 1.1
  • To add a static route for traffic to use the management network, "bigpipe mgmt route <destination network> netmask <netmask> gateway <management gateway>"[1]
  • To set a remote syslog device, "bigpipe syslog remote server"

And an important bit of data: unlike most every other damned piece of gear I deal with, the console connection for the F5 LTM is 19200 baud, not 9600 baud.

[1] For example, if your NTP server should talk to the management interface instead of one of the functional interfaces

Sunday, May 23, 2010

Return to basics.

So, I'm starting a graduate program. It's a bit nerve-wracking since my college career was a bit ... sporadic. But the first class I'm taking is "Data Communications."

I do not expect the bulk of the subject matter to be particularly challenging. :) I'm mostly going for this as a first class to ease myself back into the routine of actually doing school work and all of that.

However, I think it will be interesting to go back to the very basic principles. It doesn't look like this will be a class where they hand me a copy of the Comer book and say "Here is some hex. Decode the packet," but still, it should be interesting to go back to looking slowly at things my brain normally glosses over and take a look at Internet connectivity with a bit of beginner's mind.

Wednesday, May 19, 2010

ssh and sexism

WTTWFTVOE (Words To The Wise From The Voice Of Experience): when attempting to set up SSH on a network device (switch, router, etc), it works a WHOLE HECK OF A LOT BETTER when you remember to actually have a domain name configured.

On a different topic, I find myself fascinated by this article from, which is an excerpt from The Hidden Brain. It takes a look at a couple of instances of sex bias, from people's reactions to near-identical descriptions of a person that only vary in the gender of the person described, to comparing the experiences of two transgendered academics at Stanford - one MtF and one FtM.

I think I've been fairly fortunate in avoiding some of the high levels of sexism that other women I know have experienced in the working world. Perhaps some of it is just a comparison of IT with my previous career in the construction trades. And some of it is having ended up working with and for good folks. I've certainly encountered a fair bit, but mostly it's been at a distance as far as direct "sorry, can I talk to a real engineer" and "are you the admin?" level of stuff.

On the other hand, there's this great post from Kate fuckin' Harding about women tooting their own horn and getting past that cultural expectation for women to be demure about their abilities.

Sunday, May 16, 2010

Quickie useful link

Just a quick link: a page with undocumented cisco commands:

Wednesday, May 12, 2010

nyt: why so few women in silicon valley

By virtue of being the kind of network engineer I am, I'm unlikely to ever be a single-digit employee of a startup. By the time a company needs a full-time employee to handle the kind of infrastructure that I do, they're usually well into the scores of employees. And I haven't really done much of the startup thing. The smallest company I worked for was about 50 people, and even that was fairly well established.

I spent the entire late 1990's tech boom working for a single very large company. It was great fun, and I got to work on big networks and big projects. But it means that there is an entire subculture of the tech industry that I haven't really directly experienced very much -- that kind of technical nomadic thing that I've seen a bunch of friends in the SF bay and other areas go through, moving from startup to startup. (It also is one of the reasons that I've never been laid off, which feels like it makes me a huge outlier in the IT field!)

But even having avoided dealing directly with venture capital firms, I'm kind of appalled by this article in the NYT relaying some experiences an ex-HP manager type had pitching her company idea to VCs.
she recalls one venture capitalist telling her that it didn’t matter that she didn’t have business cards, because all they would say was “Mom.”

Seriously? It's the 21st century! Hey boys, 1975 called, and they want their chauvinism back. Also, 1975 can keep those horrible not-a-scarf-not-a-tie thing women wore with business blouses, too. We don't need those. Hates them, my precious, hates them we do.

Sunday, May 9, 2010


Here's a problem I ran into. I set up a new environment with a different layer 3 infrastructure. And everything seemed to be working. Until I got reports that some people couldn't get to one network in the new environment.

So, traffic going to the range was working great for some people, but for others, it was not -- TCP connections would connect and then fail after a few seconds.

I spent a bunch of time looking at switch ports, and spanning tree, looking to see where the blocking ports were and making sure that there's no loops. So I gave up on that line of inquiry and started tracing back at layer 3.

Sure enough, there were two routes for in one of my core routers - one of which pointed to the right place, and one of which pointed to the wrong place.

I deleted the wrong route, and things worked again.

Wednesday, May 5, 2010

Using tcpdump to only capture SYN and FIN packets

Sometimes with a network capture, all you want to know is when a session starts and when it finishes. So you don't actually want to capture anything beyond the session start and finish handshakes. Here's how to do it:

tcpdump -w flagdump 'tcp[tcpflags] & (tcp-syn|tcp-fin) != 0'

Sunday, May 2, 2010

Low Estrogen Zone

I've been working for the past few days in a big data center.

I know that I'm not actually the only woman in the building, because I've seen a woman on the janitorial staff wandering around.


About Me

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Regis has worked as a network engineer since 1994 for small companies and for large companies.