Monthly Archives: July 2013

3.1.a Identify implement and troubleshoot IPv4 addressing and subnetting

3.1.a [i] Address types, VLSM

cidr often gets jumbled in with vlsm… this is a mistake… hit it wendell…

CIDR itself refers to the administrative assignment of large address blocks, and the related summarized routes, for the purpose of reducing the size of the Internet routing tables.


explaining my summarization technique on cln…


I think that is the proper solution ,is not it?


1,453 posts since
Sep 11, 2011

i have a different way to do it, that i think is easier… the first step is determining which octet the action is going to take place… group A is a bit of a distractor, however bear in mind that within group A the third octet is always 0 and in group B you have a range of 4 (but within a block of 8). since 0 and  4 is more than 4 numbers total it can’t be /22 because 2 to the second = 4 but there are 5 numbers to include, and five isn’t reachable with 2 to the 2nd… so to get  5 numbers would require 2 to the 3rd or 8… 2 to the 3rd will include 8 numbers total…

once you have determined the power of 2 that includes the numbers, just subtract the value of that power from the classful mask… /24 – 2 = /22 (remember the action is in the 3rd octet) but that only includes 4 numbers… /24 – 3 = /21 has to be correct because it takes 2 to the 3rd to include up to 8 numbers…


3.5.d Implement and troubleshoot operations

3.5     Dual Finite State Machine (FSM)
The DUAL finite state machine embodies the decision process for all
route computations. It tracks all routes advertised by all neighbors.
The distance information, known as a metric, is used by DUAL to select
efficient loop free paths. DUAL selects routes to be inserted into a
routing table based on feasible successors. A successor is a
neighboring router used for packet forwarding that has least cost path
to a destination that is guaranteed not to be part of a routing loop.
When there are no feasible successors but there are neighbors
advertising the destination, a recalculation must occur to determine a
new successor.