Monthly Archives: October 2014

How to be a Better Speaker (19 of 30)

Now this doesn’t pertain to public speaking, which most of us won’t be doing all that much, but rather how to be better heard in meetings, especially highly technical meetings where ego can get in the way.

TLDR: Listening

It’s that simple, everyone wants to be heard, and they are not listening to you if they don’t get a voice as well. I read this somewhere (lifehacker??) several years ago and have employed the technique in my day to day since then.… Read more

IP Network Parser (18 of 30)

Assuming you have all of your configs in one directory, here is a simple script that goes through Cisco configs, parses them and outputs the network id, and netmask. Which in itself isn’t that useful, but now that you have it in a hash, there are a lot of things you can do with it. Like verify it against your routing table or IPAM, etc.. It also does two other simple checks, if the file name does not match the hostname it notifies, and it also checks to see if the interface is shutdown in order to assume it is up.… Read more

Configs Templates Take 2 (17 of 30)

This is the second part of a series of post’s on developing a Config Template tool, click this link to follow the whole series of post’s. This tutorial will go over two attributes of HTML::Template cpan module. The ability to “include” other config templates and the ability to make simple if statements.

Let’s say you have regional configs, in this example, it will be NTP servers, but it could easily be tacacs, radius, syslog, etc… You want to be able to have the user declare one option (the region,) and it correctly declare the regional configs.… Read more

Visio Tips (16 of 30)

A diagram software, is a must for a network engineer, and most of us use are probably using Microsoft Visio. Like most of my content, these topics have been covered before, (e.g. PacketLife and PacketPushers,) but I think there have been a few things not covered already, so here are a few tips.

There is a TLDR version below, so if you are impatient, skip ahead.

The biggest time saver to have is to know your short cuts. I find it painful to watch other’s right click then “bring to front” or right click “send to back.” Know your short cut’s, the one’s I know and use the most are ctrl-shift-B (move to the back,) ctrl-shift-F (move to the front,) Atl-F6 (zoom in,) and Alt-shift-F6 (zoom out).… Read more

Configs Templates Take 1 (15 of 30)

I have developed several config template systems over the years, so I wanted to write a tutorial on some of the things I have done. This first tutorial is not much more than going over HTML::Template cpan module, and having an input form, with a short demo and providing the script. As I build on each one, it will get more and more complicated. You can see a much more in depth coverage at packetlife, but this is meant to be much more step-by-step.… Read more

Cisco Symmetrical Script (14 of 30)

A while ago I had written a script that would logon to Cisco devices, run a traceroute from IP-A to IP-B then do the same for IP-B to IP-A. It would then query each hop with snmp and see if they worked out to be the same path. If it wasn’t, it would show you the differences.

I have put it up on github.

Update the below with your personal configurations

my $snmp = ‘snmp_read’;

my $ios_username = ‘ios_username’;
my $ios_password = ‘ios_password’;
my $ios_enable_password = ‘enable_password’;

Then you can run the script via cli, or send an html form to the script.… Read more

MTU 1524 on GRE Tunnels (13 of 30)

When I first came across this configuration I was confused as to how it was handling either UDP packets of 1500 bytes or TCP packets where PMTUD failed, as either an ICMP issue, or an issue where TCP did not correctly address PMTUD issues.

interface Tunnel10
ip address 10.100.100.1 255.255.255.252
ip mtu 1524
ip tcp adjust-mss 1352
tunnel source Loopback1
tunnel destination 10.10.10.10

The traditional method for fixing this issue would be to clear the df bit, set the MSS as you would normally, and lower the MTU.… Read more