VRF Race Condition

A while ago I observed an interesting problem due to a routing misconfiguration. An asymmetric route was introduced across two discrete switches/routing instances. The route was then imported in a separate location.

Quick and dirty network diagram

When I began troubleshooting I was under the impression that the importer preferred one route over another because of admin distance or some other metric, or perhaps it was some sort of BGP esoterica you’d only encounter if you were using VRFs and MP-BGP to learn routes. However, the truth was probably something more prosaic.

Both routes were static routes. This meant their learning mechanism across importers was the same. The reason the importer preferred one route over another was probably due to one entering the routing table before the other.

Dynamically monitor interfaces with Nagios

Network switches When you’re setting up your monitoring configuration for Nagios or compatible software it can be a hassle to decide which interfaces you actually want to monitor. Well rather how to monitor those interfaces. The nm_check_admin_up_oper_down plugin (part of Nelmon) checks the configuration of your network devices and reports a problem if you’ve indicated that the interface should be up.
Continue reading

Using Git with GitHub

Building on my earlier non-programmer’s introduction to Git, I wanted to talk a little bit about using Git with GitHub, a very popular service for hosting Git repositories. This post, in conjunction with the earlier introductory post on Git, will serve as the basis for a future post that talks about how to use Git and GitHub to collaborate with others on an open source project hosted on GitHub.

If you aren’t familiar with Git and haven’t yet read the earlier introductory post, I strongly recommend reading that post first.

Recall that Git is a distributed version control system (DVCS), and is designed to operate in such a way that full copies of repositories exist on multiple systems. This means you (as a single user) might have multiple copies of a repository across multiple systems. So how does one keep these repositories in sync? Generally, this would be handled via the use of a “server-side” repository to which the various repository clones are linked via a Git remote. This server-side repository might be hosted on an internal server or on a public server, and you may be connecting to it using the Git protocol, SSH, or HTTP(S). You Continue reading

2015 is all about SDN WAN

The technology that gives me a “nerd hard-on” this month is SDN WAN. Here is why.

The post 2015 is all about SDN WAN appeared first on EtherealMind.

Configuring Syslog and SNMP on a Cisco Device

by Kevin Dooley, originally published on the Auvik blog There are two common ways to get management information about your network devices

Coding Basics: Python in Visual Studio

Python on Windows with Visual Studio

Whilst I’m an OSX and Linux fan, Windows is a key operating system in any enterprise and developing network applications in a Windows environment is also an important topic to cover off. Visual Studio (VS) is a Windows IDE (Integrated Development Environment) which will also soon be available for OSX (at the time of writing, it isn’t released). Whilst I’ve brushed over this previously, this post is a quick guide on how to setup a very easy to use environment to play with Python. This is not however an in depth tool chain guide. This is a 101 post but will be enough for most people to get to grips with Python who use Windows. Let’s face it, you don’t really want to be sitting on the command line doing this do you and Eclipse is not to everyone’s taste, especially if you have prior experience coding with .net for instance.

Install the free version of Microsoft’s Visual Studio found here
Install Python 3.x (or 2.x depending on your reasons) found here
Install the Python tools for Visual Studion found here

I install both Python 2.x and 3.x as you Continue reading

Networking FAQ 4: Fundamentals

Continue reading · 20 comments

Networking FAQ 4: Fundamentals

Continue reading · 20 comments

Networking FAQ 4: Fundamentals

Continue reading · 1 comment

Netscreen Packet Capture – Snoop

I’ve worked with Netscreens for a few years now, starting with ScreenOS version 5.x, and when troubleshooting I had always been pointed towards debug flow as the way to see what was going on. I suspect many of you have also been taught:

clear db
debug flow basic
(wait for packets you wanted to capture)
undebug all
get db stream (to view output)

This is definitely helpful for rule debugging but for simple packet capture is a bit over the top, which is where the snoop command comes in.

Snoop

To be clear, snoop won’t tell you anything about what decisions the firewall made about the packets, but it’s a simple way to see the actual traffic. Here’s an example of the output produced by snoop:

19944926.0: ethernet2/1(o) len=206:0010dbff2070->00005e000101/8100/0800, tag 1872
              1.4.63.82 -> 1.15.18.27/17
              vhl=45, tos=00, id=13096, frag=0000, ttl=64 tlen=188
              udp:ports 500->500, len=168
              00 00 5e 00 00 01 00 10 db a1 27 a1 81 00 07 50     ..^........p....
              08 00 45 00 00 bc 33 28 00 00 40 11 b6 18 01 04     ..E...3([email protected]
              3f 52 01 0e 12 1b 01 f4 01 f4 00  Continue reading

IPv6 Renumbering – Mission Impossible?

In one of the discussions on v6ops mailing list Matthew Petach wrote:

The probability of us figuring out how to scale the routing table to handle 40 billion prefixes is orders of magnitude more likely than solving the headaches associated with dynamic host renumbering. That ship has done gone and sailed, hit the proverbial iceberg, and is gathering barnacles at the bottom of the ocean.

Is it really that bad? Is simple renumbering in IPv6 world just another myth? It depends.

Using GNS3 for Basic Network Security Testing

(The original idea for this post came from a post my blog, “The Console Port,” which you can find at

Fabric visibility with Arista EOS

A leaf and spine fabric is challenging to monitor. The fabric spreads traffic across all the switches and links in order to maximize bandwidth. Unlike traditional hierarchical network designs, where a small number of links can be monitored to provide visibility, a leaf and spine network has no special links or switches where running CLI commands or attaching a probe would provide visibility. Even if it were possible to attach probes, the effective bandwidth of a leaf and spine network can be as high as a Petabit/second, well beyond the capabilities of current generation monitoring tools.

The 2 minute video provides an overview of some of the performance challenges with leaf and spine fabrics and demonstrates Fabric View - a monitoring solution that leverages industry standard sFlow instrumentation in commodity data center switches to provide real-time visibility into fabric performance.

Fabric View is free to try, just register at http://www.myinmon.com/ and request an evaluation. The software requires an accurate network topology in order to characterize performance and this article will describe how to obtain the topology from a fabric of Arista Networks switches.

Arista EOS™ includes the eAPI JSON-RPC service for programmatic monitoring and control. The article Arista Continue reading

Untangle Scrutinized : Deep Dive into Untangle’s Features

This article is a followup to : Setting Up Untangle NGFW in a GNS3 Environment. In this one we take a deep dive into Untangle’s

NFD9 Prep: SD-WAN

Software Defined WAN, or SD-WAN, looks to be a theme of Network Field Day 9, with presenters such as CloudGenix and VeloCloud showing us their offerings. At first glance, SD-WAN sounds pretty compelling. Who wouldn’t want to slash their WAN OpEx? How do these solutions work, and do they have legs? I’m hoping to find out.

NB: I’ve lumped CloudGenix & VeloCloud together under the heading of SD-WAN. I’m not saying that they are the same though – I don’t yet have enough information about them to fully understand the similarities and differences. I’m sure I’ll know more in a couple of weeks!

What’s SD-WAN all about?

SD-WAN is about applying concepts of SDN to WAN networks. The goals are to increase flexibility and reduce WAN costs. This can be achieved through transport independence, dynamic path management, and better config management.

Historically we used private WAN circuits – leased lines, MPLS, etc. These had great SLAs, but the monthly costs were huge. The bandwidth was low, but guaranteed. Now that many places have access to high-speed Internet tails, it’s a lot harder to justify that cost. It’s very tempting to run IPSec VPNs across Internet links instead.

Those consumer Continue reading

Device Alias on Cisco MDS

It is definitely not convenient to configure a zone or any CFS application using WWpN. 20:ab:3d:2c:4f:89:fa:ab is not very human readable and it is definitely not efficient to keep traces of the WWpN in your MDS configuration. Device-alias is a proprietary feature created by Cisco to make your life much easier. It will map an […]

Creating a Network Community for the Network’s New Operational Models

The way in which networks are configured, deployed, and managed is changing. The network industry is in a shift from managing devices box by box via the CLI to having more centralized ways to manage and deploy devices. While the CLI isn’t going away anytime soon, we can look at the two operational models that are gaining traction within the network community.

SDN Controllers

SDN controllers do two major things that increase operational efficiencies. They offer a central point of management and visibility for the network team, but also offer a single point of integration for 3rd party systems – these systems could be anything from cloud management platform, monitoring or automation systems, to native business applications. Note: even when there are controllers being used by a human, there is risk. There is the risk of clicking the wrong button, forgetting the order of operations of which buttons needs to be clicked, etc. This doesn’t go away. Change control windows still have risk.

DevOps for Networking

We’ve also seen an increased amount of focus on the intersection of DevOps and networking. I’m really referring to DevOps automation tools and the network. For Continue reading

iPexpert’s Newest “CCIE Wall of Fame” Additions 1/23/2015

Please join us in congratulating the following iPexpert client’s who have passed their CCIE lab!

This Week’s CCIE Success Stories

James Gusman, CCIE #46507 (Data Center)
Diego de Oliveira, CCIE #46343 (Wireless)
Mohammed Basuliman, CCIE #24626 (Collaboration)
Amit Singh, CCIE #19799 (Data Center)

We Want to Hear From You!

Have you passed your CCIE lab exam and used any of iPexpert’s self-study products, or attended a CCIE Bootcamp? If so, we’d like to add you to our CCIE Wall of Fame!

Confessions of technical interviewer

A technical interviewer, or technically an interviewer. I was interviewed quite a few times since I set of to join the networking crowd, 12 years ago. I also had opportunity to sit on the opposite side, and interviewed people on multiple occasions. Some of my fondest memories of working for my current employer are connected […]

Author information

Marcin Latosiewicz

Network engineer, CCIE #25784.
Technical Services Engineer at Cisco. TAC engineer.
FlexPod wizard, Vblock charmer.
@mlatosie on twitter.

The post Confessions of technical interviewer appeared first on Packet Pushers Podcast and was written by Marcin Latosiewicz.

Layer 3 Etherchannel in GNS3

I am getting conflicting opinions on whether or not a user can emulate L3 Etherchannel in GNS3. Based on my research in this blog:

« Previous 1 … 3,663 3,664 3,665 3,666 3,667 … 3,860 Next »