Posts Tagged ‘networking’

Twittering but Which Networking Communities exist?

Tuesday, May 12th, 2009

Yes, this time I am asking you a question, so why don’t you just leave me a comment?

Fewer posts lately
First off, I would like to explain my lack of posts. I have had less creative input lately, so I can’t actually find anything interesting enough to write about to make it fun – and that’s a big part of maintaining this blog; having fun!
I’ve had some valuable input on my attempts to create a Web 2.0 IP Calculator, and I’ve had critics .. the bad, the good.

You inspire me!
I must say that the thing that inspire me the most to work is to see something I’ve created being used and from seeing Google searches hit this blog with articles directly related to the ‘googled’ issue, it gives me a good feeling inside.

Twitter
Lately, I’ve fell for the Twitter hype and you can find my tweets over at http://twitter.com/holmie, it would be fun to follow my readers on Twitter – so if you have a user there follow me!

Website statistics and the future
Anyhow, the good critics have been more visible to me than the bad ones – so I will continue this little blog experiment of mine. I can see on the traffic stats that I now have about 200 unique users every week day, except for weekends when the unique visitors drops to from 80 to 150, but there seems to be a lower bounce rate (People are reading articles about work on Sundays, preparing for Mondays?) But the traffic seems to be growing with the content, and that hopefully means that someone finds it useful!

But BACK TO THE QUESTION: Which Networking Communities exists?
I have found small forums, but where have you found study partners or other interesting networking people?
I was a member of groupstudy.com for a while, but the amount of mails where a bit overwhelming and my email client had issues with threading the mails – so I had to unregister. Maybe I will give it a second try!

Other mailing lists that I find interesting are:
cisco-nsp
extreme-nsp
foundry-nsp

Well, if you know of a good resource (a forum, website, anything!) shout it out in the comment box.

My next post will be more technical, I promise!

Multiple Area OSPF Networks on Cisco – Part 1 of 2

Sunday, January 18th, 2009

Multi-area OSPF networks are widely used, in this article I am going to show some of the logic behind multi-area OSPF Networks. I will write a series of all 2 (yey!) posts about multiple area OSPF the next couple of weeks. Stay tuned in!

Single areas can be considered subsets of a larger autonomous system.

What are the benefits of splitting networks up in multiple areas?

You can solve situations like

  1. Every time a route flaps, it initiates shortest-path-first algorithm calculations on all routers in that area.
    This causes high CPU utilization that could be used for something more productive.
  2. The routing table is getting too large and equipment that can handle less IPv4 routes will have trouble operating.
  3. The Link-state Topology table (we will get back to this) is getting unmanageable.

Terms and definitions
There are some terms and definitions that you should know:

  1. Backbone area / Transit area / area 0
    This refers to the area with area id 0, which can be a group of routers acting as the main path for traffic between OSPF areas.
  2. ABR
    Area Border Router, technically – a router that is connected to area 0 and at least another area, and therefore maintains two link-state databases are considered ABRs.
  3. ASBR
    Autonomous System Border Router is a router that are between the OSPF network and another routing protocol network, for example BGP or IGRP.
  4. IR
    Internal router, this type have all its interfaces connected to a single area.

You should be familiar with terms like LSU, LSA and the different types.

This IMPORTANT rule applies to multiarea OSPF networks:
All areas needs to be connected to area 0, if it is impossible to physically connect an area directly to area 0, you can utilize a virtual-link to create a logical path for the traffic from this area to reach the backbone area.

Different area types

  1. Standard/normal area
    A default route (0/0) is generally not generated by routers in a normal area, but it can be forced with this command under router ospf

    Router( config-router)# default-information originate always

    Normal areas (like in single area setups) can receive external route information, link updates and route summaries.

  2. Stub area
    While stub areas can’t receive external routes, they can receive inter-area routes, intra-area routes and default routes.

  3. Totally stubby area
    This area does not receive summary routes from other areas in the network, and it does not receive external routes. To reach networks outside the area it will always use the default route (0/0)
  4. Not So Stubby Area (NSSA)
    This is a stubby area which can receive a part of external routes from outside the AS.
    The LSA it can receive is Type 7 LSA.

  5. Backbone area
    ..or “transit area” always has the area id 0, every other area must have a link to area 0. Either physically or via a logical ‘virtual-link’.
  6. That was the area types, these are defined under the router ospf configuration.
    So, every 30 minute all the OSPF routers floods the area with so called LSU (Link state updates) just to make sure that every router in that area agree about the link state database. These LSUs are received by the other routers and flooded across the area until all the routers agree about the current link-state database.

    Network events and LSA flooding
    When an event happens, for example an interface goes down; the router will send a LSA and a LSU packet to 224.0.0.6 – the multicast address for the BR and BDR – which in turn will flood this packet out on all their active interfaces on the multicast address 224.0.0.5 – which is the multicast address that all routers should listen on, and they will then do the same until the network agrees about the topology and is so called ‘converged’.

    In my next post I will cover the configuration and route summarization and LSA types.

    Have a nice OSPF Sunday!