Chance to retake any failed exam free – The “Comeback” Promotion from Cisco

Cisco, through VUE, is offering a promotion from April 15 to October 15, 2008 to retake any written examination that was failed at first attempt, free of charge for the second attempt.

I think this might be very useful to those still preparing for the CCIE Written exams (or any other CIsco examinations).

Please note that both the first & the retake attempts must both take place within the promotional dates.

To learn more, please click this link.   more….

Update on CCIE R & S Written Test

As I said in an earlier post, I passed the written last week of January.

All I can say at this point is that for whoever still working towards the written exams, the best and the most comprehensive resource for the exam is the 

CCIE Routing and Switching Exam Certification Guide by Wendell Odom, Rus Healy, and Naren Mehta

This book is quite compressed and straight to the point in explaining what is covered in the exam.

Please ensure you cover not too common features like WCCP,  VRRP, DMVPN as you may get atleast 1-2 questions from each of these areas.

Also generally, a thourough knowledge of how routing protocols (especially EIGRP, OSPF) works is important as there are many tricky question to test these things. Need to know things like when EIGRP uses multicast/unicast to communicate with neigbors and EIGRP Feasible Distance (FD) calculations or that OSPF will always prefer internal routes in an area to external routes.

Talking about books, I also found the Doyles (Routing TCP/IP vol I & II) to be a good companion to the Odom’s book mentioned above.

Lastly, there are some good test engines out there that really gives you pass rate guarantee, if you really need some of these test engines that will get you the marks, please send me an email and I will be delighted to provide you their information.

Spanning Tree – 802.1d

I have read through “Cisco LAN Switching” by Clark and here are main points I was able to get out reading through the STP chapter.

 SPT uses 2 key concepts to create a loop free topology

1. Bridge ID 

2. Path Cost

Bridge ID is 8-byte field made up of bridge priority field (2 bytes) & MAC address assigned to the bridge/switch (6 bytes).

Path Cost is defined as 1000Mbps/bandwith of the link in Mbps. using this calculation to generate path cost leads to non-integer values but non-integer values are not acceptable to be used as path cost (i.e OC48 is 1000/2400 = 0.42).

Workaround is to generate new values to be used for path cost. Some example are shown below;

10Mbps ethernet link – 100

100 Mbps ethernet link – 19

155 Mbps link – 14

10 Gbps link – 2

Generally, the lower cost are always preferred. Also note that cost value in a BPDU are incremented when the BPDU arrives on a port.

STP uses the following steps for all its decision;

1 .  Lower Root BID (Bridge ID)

2.  Lowest Path Cost to Root Bridge

3.  Lowest Sender BID

4.  Lowest Port ID

2 Types of BPDU:

Configuration BPDU – It flows downstream from root bridge to all other bridges

Topology Change Notification BPDU – Flows upstream towards root bridge

Initial STP Convergence:

1.  Elect one Root Bridge

2.  Elect Root Ports on non-root bridges

3.  Elect Designated ports on every network segment in the network

Port States in STP

STP 802.1d                        RSTP 802.1w                Function

Forwarding                            Forwarding           Send/receive user data

Learning                                 Learning               Learning MAC addresses

Listening                                 Discarding            Building active topology

Blocking                                  Discarding            Listening to BPDU only

Disable                                    Discarding               Admin Down

802.1d STP Timers

Hello – 2 sec

Forward Delay (Listening & Learning States) – 15 secs each

Max Age – Time for BPDU to be refreshed – 20 secs

Default STP max. convergence time = (15 + 15 + 20) = 50 secs