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Archive of networking

Cisco IOS – concatenate output from CLI commands

January

2nd

2012

Recently I’ve been doing some work with Embedded Event Manager (EEM) on Cisco IOS.
I’ve been looking for a solution to the problem of concatenating output from multiple CLI commands ($_cli_result), finding nothing relevant.

I finally hacked my way using action regexp like this:


action 1.0 set result_var "--init--\n"
action 2.0 cli command "enable"
action 3.0 cli command "some command"
action 3.1 regexp ".*" "$result_var\n$_cli_result" result_var
action 4.0 cli command "some other command"
action 4.1 regexp ".*" "$result_var\n$_cli_result" result_var
[...]


Today I found another solution here at routerjockey.com, which uses append to populate a temporary file:


action 1.1 cli command "enable"
action 1.2 cli command "del /force flash:temp_file"
action 1.3 cli command "some command | append temp_file"
action 1.4 cli command "some other command | append temp_file"


This solution is probably nicer, even though it has the relative disadvantage of using flash storage, which may not be optimal for very frequent runs.

computing, lazyweb, networking

applet, Cisco, CLI, command, EEM, Embedded Event Manager, IOS, output

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skype 1.4 for linux goes gold

October

7th

2007

While the headline speaks for itself (here are the relevant release notes), it’s no big deal for me, since I make very little use of Skype.

There are times when I can’t avoid using it, though. Most people don’t value their freedom enough to take the most basic action or turn around the slightest annoyance, and I can’t afford not to care about all of them (though heaven knows I’m tempted).

That’s how I discovered that Skype had this very annoying habit of fiddling with the sound hardware on my notebook, randomly toggling the “capture” status and actually muting my mic during a call. After several experiments, a lot of repetitions and a whole lot of cursewords (only some of which have been heard by my counterparts, good for me), I’d come to the conclusion that it had something to do with the sound level, but couldn’t completely avoid this behaviour, no matter how low I kept my mic level or the tone of my voice.

Well, maybe the problem has been solved. This new release has a promising option switch, Allow Skype to automatically adjust my mixer levels:



to which I reply: hell no!!!

After literally months of whispering, I can’t wait to shout into someone else’s ears! Not quite enough punishment for using a closed-source, closed-protocol VoIP application, but still better than none.

Oh, almost slipped my mind: still no SMS.

computing, networking

linux, skype, sound

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Copy Criminals

April

23rd

2007



Fellow Europeans, go sign your umpteenth petition! Do it now! Let the healing begin!

It will cost you nothing. By the way, exactly what it’s worth.

Like it or not, everybody will be a Copy Criminal before long.

If you want to do something, do the only thing that makes sense: opt out. But I guess that if you’re smart enough to do that, you already figured that out for yourself… and if you haven’t…

By the way, Boing Boing says it’s urgent, so it must be.

computing, copycat blogging, media, music, networking

almost there, Copy Crime, EFF, FFII, freedom, petition

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cheap but useful trick with alias network interface

November

4th

2006

How many times did you have to change the IP address of your workstation to match the IP subnet of that new network device you needed to configure, maybe just to change its address from the default?

How many times did you need to check something on the Internet during the process, and you had to switch addresses back and forth, maybe many times? Worse still, did you like all your TCP connections such as your umpteen IM logins, ssh sessions, VPN tunnels and the like, to be shut down on the occasion?

If you do my job, it happens a lot of times. But never before this morning had occurred to me that there is a smarter way to do that, if you’re under some sort of un*x operating system like GNU/Linux(*).

Suppose you have a device on 192.168.1.1/24 (if you don’t know about CIDR, this may be a good time to learn something about it) and your workstation’s interface, let’s say eth0, is on a different IP subnet (but of course plugged into the same Ethernet network). You can do like this (as the root user):

# ifconfig eth0:0 192.168.1.100 netmask 255.255.255.0

As you may have guessed, this command adds an alias interface for eth0 called eth0:0, and assigns it the specified IP address. You can use this interface in the same ways you would use eth0, e.g. using your web browser to reach the new device’s web-based configuration interface at http://192.168.1.1 or whatever else.

The good thing is that this does not affect your main interface and the associated routing, so your existing connections don’t get killed.

Once you’re done, you can remove the alias interface:

# ifconfig eth0:0 down

and you’re back to your routine.

A couple of notes to the tech-savvy:

• (*) You can add multiple IP addresses on Windows also (from Windows 98 on, I believe). Just add a new IP address to the interface. I don’t know (nor care about) the details, though.
• Adding the alias interface automagically adds a route for the new interface’s IP subnet, but of course does not change your default route. If your new device is a router and you want to reach networks behind it, you’ll need to add specific routes to your system.
• You may unwillingly expose services running on your workstation which are listening on all interfaces (TCP *:port)

networking

device, interface, internet, linux

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Mac OS X viruses and other silly arguments about software security

May

4th

2006

Once again there’s buzz about the appearence of a Mac OS X virus in the wild. The Mac OS X virus is a lot like Elvis: one is sighted every other day.

I read and hear a lot of speculations, more or less informed, wondering if “Macintosh computers” (as in running the Mac OS X Operating System) really are less prone to viruses and other malware than “Windows computers”, or if it’s just a case of being less widespread. Moreover, the recent wind of new Macintosh ads, specifically this one, blew on the fire of this argument.

I agree with those who said that the virus ad was a risky move, because it may easily backfire out of malice or simple disinformation. But let’s look at the facts, won’t we.

The art of computer programming is still in its infancy, and that is a fact we almost invariantly fail to consider, but it’s not like we don’t know what it takes to write secure software. Actually we came to realize that there is no such thing as secure software. Every piece of software suffers from bugs and flaws, which may lead to vulnerabilities which may be exploited by malware. Suddenly I see the two golden rules:

• mitigate the causes;
• recover from the effects.

that is, in less abstract terms:

• use less error–prone designs and coding practices;
• patch early, patch often.

Under this light, Mac OS X wins against Windows in terms of security, hands down and no matter the market share, due to its design modularity, better privilege separation, ease and quick availability of upgrades.

This is not to say I am personally and completely happy with the security level of Mac OS X, since I won’t trust anything that’s not free software (beyond certain reasonable levels). Further still, I will not endorse the typical Apple user’s feeling of contempt with malware. But these are all different stories.

In conclusion, I share the feeling that Microsoft once again missed the opportunity of making something really new, and potentially secure, with its forthcoming Vista. While some early reports look promising, something tells me it will all end up just the same. Are they really “victims” of their own success? We’ll see when Vista comes out.

UPDATE 20060505: Someone at the opposite part of the globe thinks it the same way as I do. What a strange coincidence.

computing, networking, security

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