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Category Archives for "Networking"

Baby Bro, Part 3: Containers and Loops

Bro has four main container types, which I'm going to cover in somewhat nontraditional order:
  • tables
  • sets
  • vectors
  • records
Tables
A table is a collection of indexed key-value pairs: the same idea is referred to as a dictionary, associative array, or hash table in other languages. Here's a simple example that pairs letters with their place in the alphabet:


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event bro_init()
    {   
    local letters = table([1] = "a", [2] = "b", [3] = "c");
    print letters;
    }

Running it, we get this:

jswan@so12a:~/bro$ bro tables.bro
{
[3] = c,
[1] = a,
[2] = b
}

 Note that the output isn't in the same order as the script; in Bro, like in most other languages, hash tables are unordered.

Iterating over a table with a "for" loop returns the key, again like other languages:


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event bro_init()
    {
    local letters = table([1] = "a", [2] = "b", [3] = "c");
    
    for (key in letters)
        {
        print letters[key];
        }
    }

And the output:

jswan@so12a:~/bro$ bro tables.bro
Continue reading

Find link errors with op script

A new short post today for network support technicians, engineers... One thing that you usualy check when you manage a case regarding service disruption is packet loss! The first step is to check if you have packet loss at physical layer due to framing...

Find link errors with op script

A new short post today for network support technicians, engineers... One thing that you usualy check when you manage a case regarding service disruption is packet loss! The first step is to check if you have packet loss at physical layer due to framing...

Save multiple Artboards as indiviudal EMF or WMF files in Adobe Illustrator CS6

I've been creating a set of networking icons in Adobe Illustrator. To get these in a usable vector format for Visio and OmniGraffle stencils I need them in EMF or WMF format. Unfortunately the built-in Export function in Illustrator doesn't support Artboards for EMF/WMF but instead outputs one single file, so I needed to find a different solution...

First of all, I needed to split my main AI file in to individual files for each Artboard.

To do this, I went to File > Save As > Adobe EPS and selected the Artboard option.

Next was to individually export these to EMF and WMF.

First choice was to create a Workflow in Automator but for some reason. Automator's Watch Me Do action was unable to recognise that Illustrator was open - It returned some error about the application not being open (even though it was).

Second choice was AppleScript, but as it turns out Adobe don't have the EMF or WMF available as formats for the export action in their AppleScript library.

Finally I found the "Actions" menu in Illustrator.

I created a new folder called "My Actions"

Create a new Action called "Export to EMF" and started recording the Continue reading

Cisco Ironport WSA with WCCP and IP Spoofing

Recently I had to set up a transparent proxy with the Cisco Ironport Web Security Appliance (WSA) using WCCP on a Catalyst 6500 with a Sup720, with IP spoofing and web cache ACLs enabled. Like with many technologies, this turned out to be pretty simple but I couldn't find it documented all in one place. Perfect blog fodder!

The network topology looked like this (simplified, but not by much):



Normally when you set up a transparent proxy with WCCP, the IP address of the proxy server is used as the source of the HTTP requests. The problem in this topology is that I wanted the real source address of the client to appear in the firewall logs. The IP spoofing feature on the WSA allows this to happen, but it requires configuring bidirectional WCCP redirection on the Cat6k. If this had been a Cisco ASA firewall, we could have enabled WCCP there and saved some trouble, but in this case the network was using a firewall from another vendor that didn't support WCCP.

One important thing to realize about WCCP on the Catalyst 6500 with the Sup720 is that WCCP egress redirection is done with software switching rather than in Continue reading

Cisco IP Phone switchport voice vlan and CDP

I was under the wrong impression for quite a long time that Cisco IP phones require a 'switchport voice vlan ' command on the switchport that they connect to for the Phones to show up in cdp neighbors. The 'sw voice vlan ' command associates an auxilary VLAN to the port that is known as VVID (VLAN ID) for voice service. This VVID is associated with the phone during a cdp neighbor lookup. 

I thought if I didn't use 'sw voice vlan ' then my phone would not show up as a cdp neighbor on the switch. But I guess I was wrong. I set up the switchport as 'sw access vlan 80' where 80 was the Voice VLAN and I could see the phone come up, register, grab the right IP though DHCP and show up on cdp neighbors.


I had to do this because of a Cisco small business SG300 switch that we had to install in one of the maintenance offices that does not support the 'sw voice vlan id' command. 

As always, comments and feedback much appreciated!

ASA 5515-X ASDM/SSH fix

If you are planning on installing a new Cisco ASA 5515-X, or any other ASA from their 55X5-X line of ASAs, running 8.6 or above, you might run into a situation where you cannot SSH into the ASA or access ASDM.

Start off by verifying if you have activated the 3DES license. If not, grab the 3DES license key from cisco product license registration. Once Cisco emails you the activation key, console into your ASA and type 'activation-key ' under the global configuration mode. This will allow SSH version 2 on the ASA. You can verify this by doing a 'show version' on the ASA and checking the status next to 'VPN-3DES-AES'.

Next, create a username and password like you would.

username admin password cisco encrypted privilege 15

Then allow SSH on the inside and/or outside on all/specific subnets. Configure SSH version 2. 

ssh 10.0.10.0 255.255.255.0 inside
ssh timeout 5
ssh version 2

And finally allow LOCAL authentication.

aaa authentication ssh console LOCAL 

Next, you need to add an ssl encryption standard to the ASA. Most browsers and SSH/Telnet clients will reject the cipher that is present on the ASA by default.

Cisco 4500-X


At a recent new install, I had the opportunity to configure a 4500-X switch for the Data Center. It is a good alternative to a Nexus 5000 if you want 10G uplinks and are tight on budget. Of course, you will miss out on vPC and FEX which I configure are the most important features of the Nexus switches in the Data Center. But if you have 2 4500-X as redundant uplink switches, you can connect downstream devices such as UCS and SAN fabric over 10G uplinks.

Even though the 4500-X data sheets say the switch is a 32 10G SFP+ port, you have the option of using 1G or 10G GLC/SFP modules. I used a variety of copper/fiber modules to connect to routers, servers, switches and an ASA. The switch uses auto negotiation to drop down to 1G in case of copper connections. This link lists all compatible hardware for the Cisco 4500-X switch.

I had to set up a temporary fiber connection between this switch and HQ which routes to remote offices over MPLS. So for the time being, I set up a L3 port on the 4500 and set up basic static routing (ipbase does not support Continue reading

mDNS Gateway in the Cisco Wireless LAN Controller

I'm not sure why I've taken such an interest in mDNS, service discovery, and the Bonjour protocol, but I have. It probably has something to do with my not being able to use AirPlay at home for such a long time because, like any true network geek, I put my wireless devices on a separate VLAN from my home media devices. I mean, duh. So now I keep an eye out for different methods of enabling mDNS in the network in anticipation of my own experience in my home network becoming one of my customer's experience in their enterprise network.

Fixing iMessage on Hackintosh

Mid December 2012 Apple shut down the Messages Beta for Lion, soon after many hackintosh users started noticing issues with signing into iMessage. At some point in time, people far smarter than me managed to patch a little used bootloader called Clover to allow us to log into iMessage, but Clover is young and still full of random issues. Honestly, it never liked the system id on my partition, so I was never able to use it. But now, it seems that someone has patched our widely used Chameleon bootloader! I’ve tested it on my own hackintosh, and many users are also reporting success.

The instructions are simple enough, and should only take you 3 minutes + a reboot to implement and test!

  1. Download the following files to your hackintosh
  2. Execute the following commands


    3. sudo mkdir /Extra/modules
    cd /Extra/modules
    sudo unzip ~/Downloads/FileNVRAM.dylib.zip
    sudo rm -rf __MACOSX
    sudo rm -rf ACPICodec.dylib

    If you have ACPICodec.dylib in your /Extra/modules folder, you need to delete it.

  3. Unzip the Chameleon installer, and run it — make sure you install to your boot disk
  4. Reboot, and try to login to iMessage

Hopefully this will take Continue reading

Wildcard mask – What’s the difference from subnet mask?

How does the internet work - We know what is networking

What is Wildcard Masking? Wildcard mask is like any other computer IP address basically a group od zeroes and ones (o and 1). To be short, in wildcard mask all number one (1) mean “I don’t care about that position”, and all zeroes (0) mean “I care about that position in binary address”. Let’s take an example where Access list with […]

Wildcard mask – What’s the difference from subnet mask?

IPv6 over AToM pseudowire

The purpose of this lab is to show the flexibility of Layer2 VPN technology AToM (Any Transport over MPLS), which allows service providers to smoothly transit the core network from legacy layer2 technologies into a single MPLS infrastructure ready for customer IPv6 transport. Customer transition from IPv4 to dual stack is as easy as adding […]

Nexgen Storage (Part 2) – Hardware Overview

Last week I did an overview of the performance-minded storage solution that Nexgen has put together. In summary, by using SSD-based read AND write caching that’s moved in and out of the cache in an intelligent way, we can get better performance than traditional disk arrays with slower disks, and fewer of them. I’d like to do a quick tour of the hardware for their low-end model, the n5-50. It’s actually pretty straightforward and the internals are interesting enough that I decided to take some pictures and discuss their role in the solution.

Nexgen Storage (Part 2) – Hardware Overview

Last week I did an overview of the performance-minded storage solution that Nexgen has put together. In summary, by using SSD-based read AND write caching that’s moved in and out of the cache in an intelligent way, we can get better performance than traditional disk arrays with slower disks, and fewer of them. I’d like to do a quick tour of the hardware for their low-end model, the n5-50. It’s actually pretty straightforward and the internals are interesting enough that I decided to take some pictures and discuss their role in the solution.

Nexgen Storage (Part 2) – Hardware Overview

Last week I did an overview of the performance-minded storage solution that Nexgen has put together. In summary, by using SSD-based read AND write caching that’s moved in and out of the cache in an intelligent way, we can get better performance than traditional disk arrays with slower disks, and fewer of them. I’d like to do a quick tour of the hardware for their low-end model, the n5-50. It’s actually pretty straightforward and the internals are interesting enough that I decided to take some pictures and discuss their role in the solution.

Quiz #4 &#8211 BGP over ISP

Your company has more offices and each of them has a separate internet connection. The default route for each office points towards the ISP. Also, within each office you run iBGP using private AS numbers. You try to establish a BGP session between two offices, but the BGP does not come up. Why ?

Troubleshooting MAC-Flushes on NX-OS

An interesting client problem in one of our multi-tenant data centers came to my attention the other day. A delay sensitive client noticed a slight increase in latency (20 ms) at very intermittent intervals from his servers in our data center to specific off-net destinations. The increase in latency was localized to the pair of Nexus […]
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