Those non-IOS Files on the Flash. Are they useful ?

When you first receive a router from a Cisco warehouse, it comes with a complete collection of IOS add ons. A common question is whether these files are used for anything ?

EIGRP Goodbye Message

Found this in the Cisco IOS 15.1M manuals today

IP Routing: EIGRP Configuration Guide, Cisco IOS Release 15.1M&T

Goodbye Message

The goodbye message is a feature designed to improve EIGRP network convergence. The goodbye message is broadcast when an EIGRP routing process is shut down to inform adjacent peers about the impending topology change. This feature allows supporting EIGRP peers to synchronize and recalculate neighbor relationships more efficiently than would occur if the peers discovered the topology change after the hold timer expired.

show ip eigrp topology all

Once upon a time the command was “show ip eigrp topology” to show EIGRP topology, now it’s “show ip eigrp topology all” and the old command show only Feasible Successors.

PacketShaper and Flow Directions

I stumbled across an old diagram I made a long time ago about the direction of flows on a BlueCoat PacketShaper. Since I’ve been looking for it for about three years, I’ve diagrammed it quickly so that it is here for future reference when I’m working PacketWise in the future. PacketShaper PacketWise is one of my very favourite tools for managing traffic flows, and much preferable to PHB QoS aka DiffServ for many types of use cases.

An TCP flow has four possible directional attribute related to the use of a inside and outside networks, and whether the flow was initiated from the client to server which sets the “direction” of the flow relative to the Packeteer. The flow is determined by who initiated the three way handshake. For purposes here, the Client always initiates the TCP connection, and the Server terminates the connection.

TCP Session and Direction

Most people understand the three way handshake, but not many consider the direction of the session.
Packet shaper flow directions 0

The connection from the client to the server is outbound, but is inbound on the server. And vice versa, the server outbound session is inbound on the client.

Packet shaper flow directions 0 1
That’s not very useful for being able to define the direction of flows.

Why is direction important ?

Direction of flows is important if you want to configure asymmetric rules. That is, not all protocols require symmetic bandwidth. For example, HTTP traffic is usually a 10:1 ratio for reply to request. That is, a request for this webpage is about 10KB, but the reply with the data, images and javascript is more than 100KB.

Packet shaper flow directions 0 2

For an FTP upload server, you might have the reverse condition where the inbound traffic is far more than the outbound.

To make the most of your Internet connection for this case, you could configure the inbound bandwidth on your Internet connection to be 80% FTP, 20% HTTP and the outbound bandwidth to be 20% FTP and 80% HTTP. This gives a far better utilisation, especially in regards to better TCP Windowing and overall TCP goodput.

Why firewalls don’t have Telnet or SSH Clients

I found this on Cyber Corner blog:

Another missing ASA-feature: telnet and ssh client: ” Every single decent Cisco-device on earth has the ability to make an CLI-user jump to another device with telnet or ssh. Except the ASA. I really wish that this feature could be added. Right now I am troubleshooting a firewall and from where I am right now the only way in is to SSH to the ASA. I can do whatever I want inside the firewall from my SSH-window, but I need to access a router inside of that firewall, and if this feature wasn´t missing i could simply run ‘ssh ip-address’ to jump to the switch´s CLI.

Am I the last CLI-.guy on this planet? Please, Cisco? 

Fate Sharing, Failure Domains and why VTP is awesome

A lot of people regard Virtual Trunking Protocol(VTP) as nothing but trouble. Indeed, it’s hard to find many people who will implement it on their network. I find this baffling – it’s a great tool that dramatically reduces time, errors, and troubleshooting is something that we should all embrace and use wherever we can. Naturally, with great power comes great evil. So, lets be clever instead.

Fault Detection in Metro Ethernet

Following my article on Loop-Free Alternate Routes, Michael McNamara made a good point about some of the issues detecting failure in a Metro Ethernet network. This seems to be a commonly misunderstood problem.

Citrix Branch Repeater Authentication with Cisco TACACS+

I have been looking about for documentation on how to configure TACACS authentication with a Citrix Branch Repeater, however so far I have only been able to find documentation for NetScaler. So I have setup a LAB and decided to write the documentation myself. For those who cannot be bothered to read this post there […]

Verifiying IPsec and SSL Performance of ASA Firewall

It’s difficult to a get any documentation from Cisco that confirms the forwarding performance of the ASA firewall. However, once you have got a unit, the “show crypto acclerator statistics” is a handy way to verify and check the hardware performance of your ASA. I think that most of this output is self-explanatory so I’m […]

Cisco IP Traceroute Characters

Note to self about Cisco Traceroute characters and what they mean. Directly from the Cisco IOS user documentation.

Cisco IOS CLI Shortcuts

Mostly for my own reference. I really need to practice using the Delete Buffer commands and Ctrl-R Refesh as part of my muscle memory.

Three ways to fix the Cisco IOS Translating “xyz” Domain Server

Fixing the Cisco IOS Domain Lookup – three different options.

TCAM – a Deeper Look and the impact of IPv6

The thing about TCAM memory is that it can be big killer for IPv6 migration. Why ?

So you want to use a 3750-X as a Router?

Easy peasy lemon squeezy This seems a straightforward question! Just load up with advanced IP services license, install the license file and reboot the switch and you should be good to go. Well that’s what I thought until recently when I done the very steps above and on the surface seemed okay but I wanted […]

Bluetooth hangs in OSX 10.6.6

Occasionally my Bluetooth gets all wrong. Here is quick and brutal fix for bluetooth hangs on OS X.

Cisco IOS SX Storm Control

Blurt on Cisco Storm Control

Putty – Fixing Right Click Paste

Fixing the Right Click Paste action of PuTTY to prevent mistakes when copy and pasting.

Remote (in band) configuration tips

However working on a Global network, especially if you are making changes in-band and you don’t have the facility to access the system via a remote console or have remote power control(For people who do have such infrastructure I am insanely jealous), then you need have a few outs to keep you out of trouble. I thought I would share some useful tips that help minimise risk for you when doing remote changes.

RFC 5952 – A Recommendation for IPv6 Address Text Representation

At last, some decent rules on the RIGHT way to write IPv6 addresses.

The Ancient and Noble Art of Troubleshooting

Troubleshooting, itís something we all do. It may be your parents Internet connection, the company photocopier, your kidís car or the core network of a medium sized bank. However, troubleshooting is not like that, itís more like football, years of watching and playing does not guarantee to make you a superstar. However, with troubleshooting, just like football, it does teach you enough so you have an opinion on how it should be done.

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