October 14, 2009

Cisco IOS Tips - cache running-configuration

This is probably one of the most ignored and forgotten feature of IOS since 12.2(25)S and 12.2(27)SBC. I am positing it here as I never stopped coming across routers and switches with this feature not active. Please note you need to enough memory,to use this feature; that is to say, the available space in memory to hold a copy of the interfaces configuration. As you may guess, a router or switch with a monstrous configuration, can take a while to display the running configuration when issuing ... Read more

October 1, 2009

OSPF BDR DR election process

This post assumes that you have a basic understanding of OSPF… if not, I suggest jumping over http://en.wikipedia.org/wiki/OSPF for a first quick read. However for the sake of this post, I will go over some basic reminders. The “hello” packet The OSPF routers sends a periodic packet referred to as the hello packet ‘multicast 224.0.0.5’ which is composed of the OSPF header + different fields ID necessary for routers to neighbor and become adjacent. ... Read more

September 20, 2009

Filter networks with BGP

There are 3 easy ways to filter/restrict certain networks to be announced through BGP to a remote/adjacent AS (Autonomous System). Those 3 simple ways include: prefix-list | Extended Access-list + Route-map | Extended Access-list + Distribute-list To Note: before we go on, I need to specify that creating an extended access list to be in use with BGP (route-map, distribute-list) is almost as similar as creating a prefix-list… Having said that, we are therefore no longer matching source and destination address but merely address prefix and netmask with the access list. ... Read more

September 19, 2009

Cisco Switch Ether-Channel - misconceptions

I decided to write this post to address some of the many misconceptions out there on many mailing lists, forums etc… 1. More bandwidth That is one of the first common misconception I often read or hear, if I “trunk” (Solaris term actually) many ports together, the number of ether-channeled port is equal of the number of ports multiplied by the bandwidth of each port. In other words… 8 * 100Mbps port ether-channeled would create a single logical port with 800Mbps… Now while this is somewhat the anticipation, it isn’t really true. ... Read more

September 16, 2009

Cisco IOS Configuration boot register - ROMMON

Every cisco routers has a configuration register which is saved in NVRAM and is a 16 bit value. This post will not tackle all the 16 bits of the configuration register, but only the 13th bit which is used to either load IOS or ROMMON. Another post will be made to detail all the 16 bit configuration register. Before continuing, it is important to understand the basic “boot process” of a router. ... Read more

September 15, 2009

Cisco IOS shortcuts

Configuring Cisco IOS shortcuts command are quite easy and neat… just use the exec command “alias”. command structure: alias Example in exec mode: sh ip int br (show ip interface brief) so following, we would get “alias exec s sh ip int br” Example in configure mode: router ospf and we would get “alias configure ro router ospf” More mixed examples [ alias / original command / command to enter ] ... Read more

August 26, 2009

Cisco IOS hidden tools

Hello there, Just a quick overview over a couple of cisco hidden command useful in certain circumstances 1. ttcp ttcp is only available on routers/layer 3 switches (of course ;-) ) For those familiar with iperf, ttcp is a kinda”ish” iperf Start ttcp on one router in point 2 point scenario and ttcp on the other endpoint. One router will be in receiving mode, while the other will be in sending mode… running the command is quite straight forward, thus I will not demonstrate it here. ... Read more

April 25, 2009

Cisco Datacenter Blueprint

If you dream of Cisco Routers and Switches like me If you can’t help it but swear by Cisco (beside their load balancers, let’s be honest it sucks) If you tried to convince your wife to have each room of the house on a different subnet then you need to download this … http://alouche.net/cisco/data-center-poster.pdf **** the following poster is provided and copyrighted freely by Cisco Inc…