Kevin Dorrell, CCIE #20765

15 Mar 2010

The BGP Decision Process

Filed under: BGP, IP Routing Protocols — dorreke @ 12:29

As it is coming up to re-certification time, I have dusted off my copy of Wendell Odom’s CCIE R&S Certification Exam Guide. I have the second edition, which is a little out of date but the information in it is still relevant.  With that, and the addition of sample chapters from the 3rd edition about MPLS and IPv6 courtesy of the CiscoPress web site, I hope to get by without forking out for the new 4th edition.   (That is one advantage of not registering my copy until 3 years after I bought it: CiscoPress gave me two sample chapters from the 3rd edition to try to persuade me to buy it, even though that too is now out of print.  But I digress.  Who knows, I may crack and  buy the 4th edition anyway.  I’m a glutton for books.)

I am looking at the BGP Decision Process on page 444, and I am having an issue with steps 3 and 5.  Just as a reminder, here are the steps as explained in the book:

3. Locally injected routes – Pick the route injected into BGP locally; if multiple routes exist, prefer ORIGIN I routes first, then ORIGIN E routes, and finally ORIGIN ? routes.  (This step is seldom needed, and is sometimes omitted from other BGP references.)

5. ORIGIN PA – IGP (I) routes are preferred over EGP (E) routes, which are in turn preferred over incomplete (?) routes.

Now, I may be being thick, but I don’t see the difference between these two steps, and I am suspecting that the explanation of step 3 is incomplete.  I suspect step 3 has nothing to do with the ORIGIN PA, but has all to do with whether the route was generated by a network command or by redistribution on this router.  Or maybe it means that the ORIGIN PA values are compared, but only if the routes are locally generated.  As he points out later in the chapter, the step is largely redundant because locally generated routes would get a weight of 32768, and so would have won outright at step 1.  But my confusion is compounded on page 456, which insists that the step is related to the ORIGIN PA.

OK, the way I think it probably works is this: step 3 gives preference to routes generated in this router by a network or redistribute command.  In fact, they have already been given preference by virtue of the weight of 32768 that they were given,  but just suppose for a moment that they are competing with an incoming update that has been artificially given a weight of 32768.  The locally generated ones take preference, discarding the incoming route.

Now suppose we generated the route locally twice, once by a redistribute by a network command.  Both of these will drop through step 4 since the AS_PATH is still empty.  So even in this case, it is step 5 that decides between I, E, or ?.

I think I’ll have to write to him to ask about it.

14 Feb 2010

Home lab

Filed under: Uncategorized — dorreke @ 14:29

I just decided to fire up my old home lab, and found I did not have a cabling diagram.  So, here it is.  The lab is pretty well a full mesh of various old, and even older technologies.  It is based on the NetMasterClass pod, but with extra connections – well, there is no point in wasting unused interfaces.  The idea is that if you have a full mesh, you just enable whatever interfaces you need to make whatever topology you want.

Click of the diagram for a hi-res PDF version:

02 Feb 2009

Networkers 2009

Filed under: General, IOS features, LAN Switching, Security — dorreke @ 20:10

Networkers 2009 is all over now, and things are getting back to normal.  So what did I take away from the conference?


I mean the other sort of networking: the human network.  It was good to finally meet some of my fellow bloggers: stretch and Ethereal Mind, for example. It was also good to meet marikakis again, a colleague in the NetPro discussion group.

Talking of this sort of networking: “Network Management” can mean different things to different people.  A colleague once booked into a “Network Management” seminar, then found out that the seminar was about how to manage a company by leveraging person-to-person “networks”.

802.1X Techtorial

I spent a whole day looking at 802.1X.  Actually a significant part of that time was spent looking at Cisco’s ACS (Access Control System).  The two or three days follow gave me a chance to reflect on the tool, and chat to the people on the security booth.  The more I reflected, the more I was convinced I need to do an 802.1X project.  I also bought a book about security, and I might even consider going down the security track when my CCIE comes up for renewal.

IOS Instrumentation

Two of my sessions dealt with the interesting and fun recesses of IOS.  The BoF session was really an opportunity for Cisco to brainstorm about these features.  There is a ton of stuff in IOS that is very rarely used: stuff like the EEM (Embedded Event Manager) TCL scripting.  There is a community dedicated to these features at ciscobeyond. One of the conclusions we came to was that Cisco has not made a very good job of publicizing these features.

The other session relating to this was “13 Smart Ways to Configure Your Cisco IOS Network Elements”.  This was a really fun session that, “like all bad ideas, was formulated over a beer”.  It was a bet, based around “there must be at least a dozen ways to configure a router.”   EEM is only one of them, and there are well more than the 13 the speaker listed.  I can’t wait to get back to the lab to try some of them out.

VSS and layer-2 architectures

I went to several sessions about VSS, both in campus architectures and the data centre.  I detected an interesting change of emphasis over last year’s offering.  Last year they were still pushing pure layer-3 architectures.  At the same time I was struggling with how to split a server cluster over two sites.  Over course, this is not easy to do with a layer-3 architecture; you need at least one layer-2 interconnect to carry the heartbeat.

This year, they seem to have woken up to the need for a layer-2 interconnect between the data centres.  They offer VSS as a way to provide redundancy for that interconnect.  I still stubbornly use Rapid Spanning Tree for various reasons connected with my architecture, which makes me feel a distinct minority.  I suppose you can get away with it provided there are not too many hops between the data centres.

Advanced BGP

I always try an attend a session by Russ White if he is there.  His style is eclectic, to say the least, with about 50% of the time spent on anecdote and sidelines.  That’s what makes the presentation memorable and entertaining.  Must be confusing for anyone whose native language is not English tho`!  Good guy, and what a huge knowledge base!

Other stuff

Just a few more observations:

  1. The “World of Solutions” was tiny compared with previous years, so full marks to those who did attend.  Companies must really be feeling the pinch. I was impressed with SolarWinds for taking the time to show me their Orion network management centre.  No marks for Computer Associates, who I wanted to grill about my problems with their Spectrum product, but who did not attend this year.
  2. I was impressed with the Nexus 1000v virtual switch.  This is an add-on to VMware and replaces the ESX virtual switch.  What it does is to make one huge virtual switch across your VMware domain, which means you can apply policies to invidual virtual machines: policies that move with the machine whenever it goes vmotion.
  3. I’m getting too old for the Cisco party.  It was a bit entertaining, but a lot brash and noisy.  The best Networkers party was the one in Monte Carlo in 1995, or the one in Vienna in 1999 (?), with a group that covered a range of musical tastes, not just hip hop, punk, and rap.
  4. The keynote address by Prof. Brian Cox was cool, but not very much to do with networking.  He could have tied in the theme of collaboration a bit more explicitly.

28 Jan 2009


Filed under: Uncategorized — dorreke @ 10:25

I have been having so much fun at the Networkers conference in Barcelona since Monday that I have not got round to blogging anything yet. So, just to take the lead from stretch, here is my schedule:

Monday 26th January:

  • 09:00-18:00 : 802.1X deployment in a campus LAN (all day session)
  • 18:15-19:45 : BoF Myths and Realities of self-managing networks

Tuesday 27th January:

  • 08:30-09:45 : Keynote address from John Chambers
  • 10:15-12:15 : Multilayer Campus Architectures and Design Principles
  • 12:30-14:00 : Understanding Network Management using the ITIL Methodology and Framework
  • 14:30-15:45 : Talk by Prof. Brian Cox about the Large Hadron Collider
  • 16:15-18:15 : Advanced Cisco Catalyst Virtual Switching System

Wednesday 28th January

  • 08:30-10:30 : QoS Decomposed
  • 11:00-11:45 : Cisco on Cisco : Inside Cisco IT
  • 12:00-12:45 : Leveraging VSS for Data Center Interconnect
  • 13:30-15:00 : Data Center Virtualization Overview / Concepts
  • 15:30-17:30 : 13 Smart Ways to Configure Your Cisco IOS Network Elements
  • 19:30 onwards : The Networkers Party !!!

Thursday 29th January

  • 08:30-10:30 : Advanced New Developments in BGP
  • 13:30-15:30 : Advanced Enterprise Campus Design : Leveraging VSS

Friday 30th January

  • 13:40 : flying home !!

So, what do I think of it so far, as I sit here in the CCIE wireless lounge with my cup of coffee?  Well, I think I have had an object lesson in preparation.  I always enjoy the Networkers tutorials, but I am sure I would have got more ot of them if I had been better prepared, particularly for the 802.1X techtorial on Monday.  Proper preparation for such an event would have had two distinct benefits:

  1. Preparation opens the mind to receive the new information.  If I don’t prepare the neuron pathways well, then I understand the talk as I hear it, but I don’t retain enough of the information.  The information just does not make the transition from hippocampus to grey matter.
  2. Preparation provides a foundation on which any new information can be built.  If I spend the entire talk refreshing my existing knowledge, I cannot concentrate on adding the new stuff.

That’s it for now.  In 20 minutes I am in to “Cisco on Cisco”.  I think stretch is booked in for that session too, so I hope I identify him.

21 Jan 2009

Starting a new blog – LX2KD

Filed under: Uncategorized — dorreke @ 15:56

While I was studying for my CCIE, I found blogging was a really useful way to journal my studies.  The advantages over pen-and-paper are enormous: it is searchable, it creates social bridges with like-minded peopl, it imposes discipline, etc.

But networking is not the only thing I do that would benefit from a journal .. oh, no.  Amateur radio is another.  It wouldn’t be fair to mix my amateur radio activities with my networking stuff.  So I am starting a new blog thread: the “LX2KD / G4AZO”.

So anyone who is interested, see you over the other side. (But allow me a day or two to get started please.)

01 Jan 2009

Now where was I?

Filed under: General — dorreke @ 21:25

Well, it’s about 6 months since I last posted anything on my blog, and it’s about time I re-activated it.  I’ve not been completely idle over the six months, but I have been doing things that don’t really relate to CCIE: scouts (Telstar troop), amateur radio (LX2KD / G4AZO), music (guitar), swimming, etc.  Not even my computer/network related activities have been directly CCIE related.

I got an e-mail from Wael Osama the other day with a pointer to a blog called “Networkers Online”.  This confused me at first because it has the same name as the Cisco conference.  But in fact this is a very interesting and competent coöperative blog, written by several engineers.  See my blogroll for the link.

BTW, talking of Networkers, I shall be going to the Cisco Networkers conference in Barcelona on the last week in January.  I have booked in for the 802.1X techtorial, which should be interesting as it is a subject I do not get to use on a daily basis yet.  Are any of my readers going?

So, we have a New Year, and a resolution to blog a bit more often.  A very Happy New Year to all my readers.

04 Jul 2008

Who works for who?

Filed under: General — dorreke @ 21:14

It’s getting like a game of musical chairs.  First we had the announcement a couple of weeks ago that Scott Morris was moving to InternetworkExpert.  Scott had previously been the mainstay of IPexpert.

Now we have an announcement that Narbik has joined up with IPexpert:

IPexpert and Narbik Kocharians Join Forces

 It is with great excitement that we reunite with Narbik Kocharians to offer the most incredible CCIE training value available anywhere! Narbik is a well-recognized triple-CCIE with an outstanding name in the CCIE training space, known for his unique style and magnetic personality. 

Read the full story here.

There seems to be a bit of a ratings war going on between the big three: IPexpert, InternetworkExpert, and NetMasterClass.  I am gratified to see that I am on the “success stories” list of all three, having used materials from all three.  I would always recommend that any candidate should use materials from at least two vendors, otherwise you can get too used to the way a particular vendor phrases his questions.  (P.S. Sorry, I forgot CCBOOTCAMP, which should also be considered one of the “big four”.  I forgot them just because I have not used their materials yet.)

22 Jun 2008

Gripes about my HP Photosmart 3210

Filed under: General — dorreke @ 14:51

This has nothing to do with CCIE.  I’m just using my blog to gripe about an unsatisfactory piece of software.

I have one of those HP All-in-one printer-scanners, the HP PS 3210.  Overall, it works fairly OK, but I do have a number of gripes about it, especially when used on the home network.  I would be very interested to know if these problems are still present in the more recent all-in-one models.

1. Multi-user scenarios

We have Windows XP on the family computer, and an account for each member of the family.  This doesn’t interact too well with the print driver, especially if you try printing double-sided.  The driver has a feature for printing double-sided: basically it prints the odd numbered pages first, then you turn them over manually, then it prints the even numbered pages.  (Or is it first the evens, then the odds .. ?)

Anyway, you get a pop-up telling you when to turn the pages over, and it doesn’t print the other side until you click “Continue”.  Trouble is, the pop-up comes up in the context of the first person to log in, which is not necessarily the person who asked for the print job.  (Some members of the family have the bad habit of leaving their desktops logged in.)

I tried getting support from HP on this, but they said it was too difficult to fix so they were not going to do anything about it.  Great!  Lots of wasted paper.

2. Must be always powered on

If you start the PC with the printer switched off, then you are in trouble.  The trouble occurs not when you start the PC, but when you try and shut it down.  It comes up with lots of “Program not responding” pop-ups, and does not close down until you kill the HP software by hand.  Is it unreasonable to expect them to have thought of that scenario?

3. Cannot update software any more

This is a knock-on effect from my attempts to solve the double-sided issue.  When I contacted HP support, of course, I got the usual “Are you running the latest version of the driver?”  So I downloaded and installed the very latest version I could find on the web site:  Since then, the automatic software update does not work any more.  It seems to download the files OK, counting the bytes, but then says “Download failed”.   There are several “critical” updates I have not been able to install.

4. Default scan profile not applied to multi-page TIF documents

Being European, I have a default scan profile corresponding to A4 paper.  Definition: 1/16 m² with an aspect ratio equal to the golden ratio, ((sqrt(5)-1)/2).  When scanning a single page document, this works fine.  When scanning a multi-page document, it works fine for the first page.  But for subsequent pages, I must re-apply the profile manually to each page.  That slows me down.  (P.S. Strangely, this happens only if you enable the preview.  If you don’t preview, the profile is applied to all the pages.)

5. B/W threshold is different if previewed.

When scanning in black-and-white, you can set the B/W threshold to determine how light or dark you want the image.  The range goes from 1 (very light) to 255 (completely black).

If I preview the scan, I need a B/W of about 120 for a reasonable copy.  If I don’t do a preview, a setting of 120 gives a very light washed-out image.  Unfortunately, the only way I know to edit the profile is do do a preview, which doesn’t make the adjustment of the non-preview setting very easy.  After a lot of experimentation, I found that a B/W threshold of about 164 gave the correct result in non-preview.

Why couldn’t they make the settings behave the same in preview and non-preview modes?

6. Scanner goes into non-responsive mode.

There seems to be no rhyme nor reason to this.  Sometimes the scan software goes to sleep for up to two minutes just after it has populated the preview window, but before I can click “Accept”.  Sometimes, it gives me back control within two or three seconds.  I have no idea why the difference.  During this time, TaskManager tells me that the CPU is 99% occupied, running the process hpscnvw.exe.

Further Comments

Just in case someone comes across this blog and has the same problems, here are some more things I found out:

Issues 5 and 6 are actually related.  I found out that the “going to sleep” depended on the page being scanned.  I was scanning some old documents for the archives.  These documents were on slips of paper of format 1/3 A4: about 8″ by 4″.  These particular documents had some areas with a mid-grey background, and that was being converted to b/w dot-screen for the purposes of the preview.  That is what was taking the time.

If I ask it to scan without a preview, the whole image comes out a lot lighter, and in fact the mid-grey background gets lost.  It can therefore present the scanned slip in about 15 seconds instead of 2 minutes.  I think I can live with that – at least the printed parts are still legible.

18 Jun 2008

Ethan is back!

Filed under: Uncategorized — dorreke @ 17:11

It’s good to see you back on line Ethan!


12 Jun 2008

Ha-Ha! Gotcha!

Filed under: General, LAN Switching — dorreke @ 10:40

Well, they say it is good to be able to laugh at yourself …

So, I took this nice new 2960G-24TC, and I placed it front-down on the floor so I could get at the back panel easily, and I plugged in my console cable, and my power cable, and … absolutely dead!

So, I pick it up to work out what is going on, and it suddenly comes up with:

Base ethernet MAC Address: <omitted>
Xmodem file system is available.
The password-recovery mechanism is enabled.

The system has been interrupted prior to initializing the
flash filesystem.  The following commands will initialize
the flash filesystem, and finish loading the operating
system software:


So, I unplug the power cable, and plug it back in again, and it comes up with:

Base ethernet MAC Address: <omitted>
Xmodem file system is available.
The password-recovery mechanism is enabled.
Initializing Flash...

So I put it back down on the floor …. and nothing more happens … until I pick it up again! Etc.

This went on for a good five or ten minutes.  What is going on?  I suppose it is obvious to anyone that has already fallen into this trap!


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