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Networking

How to test bandwidth between Linux hosts

First of all, make sure you have iperf installed on both hosts.

If you haven’t, then use the following command to install it. I will be using Ubuntu flavour linux for demonstration.

apt-get install iperf

Pick one host as Server, one host as Client.

On the server issue the following command

iperf -s

One the Client, issue the following command

You can find the Server_IP by using ifconfig -a on your host

iperf -c Server_IP

See the following example for more info

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How to connect USB Serial Console Cable to Linux

The following guide will walk you through on setting up USB Serial Console Cable on a Linux via command line.

First of all, make sure you have a program called Minicom installed.

I will be using Ubuntu flavored Operating System for demonstration purposes.

apt-get install minicom

Then you need to connect the USB Serial adapter and find out which serial port is it connected to.

dmesg | grep USB

You will see something similar to this output.

[    6.804403] usb 1-1.3: pl2303 converter now attached to ttyUSB0

Make sure you chmod 777 /dev/ttyUSB0 so minicom will allow you to save the config.

Open up minicom by running the command minicom -s and select Serial port setup

Reflect the output you saw from dmesg and set it to the Serial Device by pressing AE > C

A – Serial Device : /dev/ttyUSB0
E – Bps/Par/Bits : 9600 8N1

Please see the following screenshot for more info.

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Configure WPA2 (AES-CCMP) on Cisco 877w

It is possible to configure WPA2 (AES-CCMP) on a Cisco 877w Router and these are the steps required to achieve them.

First of all, do make sure you have the right IOS version. This is important because some versions of the IOS does not support the latest WPA2 Key Management type along with AES-CCMP Encryption. This configuration is based on the following IOS.

Cisco IOS Software, C870 Software (C870-ADVIPSERVICESK9-M), Version 12.4(22)T5, RELEASE SOFTWARE (fc3)
c870-advipservicesk9-mz.124-22.T5.bin

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Cisco 877w with External Modem (RFC 1493 / IPoATM)

The following configuration is for BE Broadband / O2 Broadband Specific and will work with an external modem working on RFC1493 / Bridge mode.

When it comes to setting up a Cisco Router with a modem under bridge mode, you only need a Layer 3 port to configure the given IP Address. In any Layer 3 capable device, it is rather straight forward. To configure, you only needs to add the IP address, subnet mask to the interface; along with the default route to the ISP given default-gateway and it should work.

When it comes to the 877 / 877w etc, they only come with 4 Layer 2 capable switch port, therefore one needs to configure a VLAN Interface and assign one Switchport to the given VLAN as per following configuration.

You do not need to create a Dialer Interface as PPPoE/PPPoA is not involved in this configuration.

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Would Cisco Consider Releasing an IOS Emulator

Overview

I have been seeing a number of articles on the Internet trying to persuade Cisco to offer some kind of real-time emulation software for their IOS. I remember Greg Ferro from Etherealmind started a petition a while back and I have yet to see any development on that…

The fact that the matter is, Cisco already have such platform called IOU, which is designed to emulate their IOS to a near hardware experience for their internal testing environment. (Don’t quote me on this, but this is pretty good from what I have heard, or researched)

Currently we have Dynamips, which is one of the resource hungry Cisco Hardware emulation platform where testing can be done to a certain extend but it is nowhere near perfect, and here are some facts.

  • Dynamips does require a Lot of resources.
  • This is extremely processor heavy.
  • QoS does not work very well.

If you want to have a detailed explanation on, please have a look at the following post by Wendell Odom who explains thoroughly on the NWW.

What puzzles me is the fact that Cisco goes out of their way to promote their Educational sector, yet they are reluctant to offer some kind of Software Emulation to accommodate their IOS.

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How to Unzip / Uncompress Cisco IOS

This procedure is quite simple and the following is done on Linux. When you have an uncompressed IOS, you don’t need to wait for it when it comes to loading it on Dynamips. unzip -p c3725-adventerprisek9-mz.124-25.bin > c3725-adventerprisek9-mz.124-25.image You can see both compressed and uncompressed versions below. Workstation IOS # ls -ltrh |grep 3725 -rw-r--r-- 1 root root 38M 2010-11-29 16:47 c3725-adventerprisek9-mz.124-25.bin -rw-r--r-- 1 root root 79M 2010-11-29 20:23 c3725-adventerprisek9-mz.124-25.image Workstation IOS #

TCP Window Calculation

I was going through some TCP windowing over a high speed WAN link, and thought it might be worth to post some info regarding this. We do face a typical problem of having slow speed file transfer even if the dedicated pipe is capable of supporting it. There are three factors which affects this… TCP Window Size. Round trip latency of the circuit. Bandwidth of the circuit. Maximum throughput you can get from a line with 10ms latency and a TCP window of 32KB can be calculated with… 32KB –> 32 x 1024 x 8 = 262144 Bits 262144 ÷ 0.01 = 26214400 bps = 26.2144 Mbps Let’s say we have an OC-3 line, which is at 155 Mbps and a round trip latency of 10ms, and we need to calculate the TCP window size to maximize the throughput… 155.52 x 106 = 155520000 bps TCP_WINDOW = 155520000 x 0. Read more