Sep
07
Fast Convergence for Designated Ports RSTP protocol's fast convergence depends on the use of point-to-point links connecting switches. In order to quickly transition a designated port into non-discarding state, the upstream switch needs to make sure that the downstream neighbor agrees with that idea. This constitutes the process known as handshake (or proposal/agreement): Upstream bridge sends a proposal out of a designated port. As a matter of fact, it just sets the proposal bit in outgoing... Read More
Aug
10
In this blog post, we will obtain some good solid Tier 1 level knowledge regarding VLAN Access Control Lists or VACLs. These are often also referred to as VLAN Access Maps or just VLAN Maps; thanks to the syntax that is used in their creation. When you want to filter traffic that is moving from one VLAN to another, things are real CCNA-like and friendly :-) We use an Access Control List. In fact, we should elaborate on that term a bit now in light of this discussion. We actually use a... Read More
Mar
14
We are going to discuss Cisco’s proprietary extensions to STP algorithm, namely UplinkFast and BackBone Fast. Those two features aim to reduce the time it takes STP to re-activate topology after a link failure. While UplinkFast seems pretty intuitive, BB Fast is more complicated. See more detailed overview at: http://blog.ine.com/wp-content/uploads/2010/04/understanding-stp-rstp-convergence.pdf UplinkFast Read More
Mar
07
In this post we are going to look into STP convergence process. Many people have perfect understanding of STP, but yet face difficulties when they see questions like “How many seconds will it take for STP to recover connectivity if a given link fails?”. The post will follow the outline below: 1) General overview of STP convergence process 2) How STP converges if a directly connected link fails 3) How STP converges when it detects indirect link failure 4) Topology changes and their effect See... Read More
Feb
04
We see our students at all levels sometimes struggle building a network from the "ground-up" using a logical topology diagram. Let us use this blog post to examine a portion of a logical diagram and discuss how one could most easily and accurately setup the network. Read More
Jan
14
Here are two announcements from Cisco regarding the addition of an “open-ended question” portion to the R/S Lab Exam. The first is the recent announcement, while the second is from August of 2008 when they were testing the process in Beta in China. Cisco has indicated on their forums that they will eventually update all tracks with this new open-ended question exam section. They will be making announcements prior to those track changes to give us the exact date of change. Read More
Oct
30
In this post we will look at the basic classification and marking features available in the 3550 and 3560 switches. Basic features include packet marking using port-level settings and port-level policy-maps. Discussing Per-VLAN classification is outside the scope of this document. The Catalyst QoS implementation bases on Differentiated Services model. In a few words, the ideas of this model could be outlined as follows: 1) Edge nodes classify ingress packets based on local policy and QoS label... Read More
Sep
24
Note: You may want to read a newer blog post on MSTP here Understanding MSTP Read More
Sep
11
People are often confused with per-VLAN classification, policing and marking features in the Catalyst 3550 and 3560 models. The biggest problem is lack of comprehensive examples in the Documentation CD. Let's quickly review and compare traffic policing features available on both platforms. The material below is a condensed excerpt of several Catalyst QoS topics covered in the “QoS” section of our IEWB VOL1 V5. You will find more in-depth explanations and large number of simulation-based... Read More
Aug
04
More updates have been posted tonight to the CCIE Routing & Switching Lab Workbook Volume 1 Version 5.0 Beta on the member’s site. Bridging & Switching, Frame Relay, IP Routing, RIP, and EIGRP are now posted. Also there is a new feature that indicates when the files were updated last, so you will always know if you have the most current version. Read More

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