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ICND1 – IP Address

June 16th, 2017 in ICND1 100-105 Go to comments

Question 1


The RFC 1518 is Classless Interdomain Routing (CIDR). CIDR is a mechanism developed to help alleviate the problem of exhaustion of IP addresses and growth of routing tables.

The problems were:

+ With the classful routing system, individual networks were either limited to 254 hosts (/24) or 65,534 hosts (/16). For many network enterprises, 254 hosts were not enough and 65,534 were too large to be used efficiently.
+ Routing information overload. The size and rate of growth of the routing tables in Internet routers is beyond the ability of current software (and people) to effectively manage.
+ Eventual exhaustion of IP network numbers.

To solve these problem, CIDR was selected as the solution in 1992.

In contrast to classful routing, which categorizes addresses into one of three blocks, CIDR allows for blocks of IP addresses to be allocated to Internet service providers. The blocks are then split up and assigned to the provider’s customers.

According to the CIDR standard, the first part of an IP address is a prefix, which identifies the network. The prefix is followed by the host identifier so that information packets can be sent to particular computers within the network. A CIDR address includes the standard 32-bit IP address and also the network prefix. For example, a CIDR address of, the “/26” indicates the first 26 bits are used to identify the unique network, leaving the remaining bits to identify the specific hosts.

Therefore, instead of assigning the whole block of a class B or C address, now smaller blocks of a class can be assigned. For example, instead of assigning a whole block of, a smaller block, like or, can be assigned.

In fact, CIDR is specified in RFCs 1518,1519 and 1520 so answer “RFC 1519” is also acceptable.

Question 2


In order to send traffic to multiple devices (not all) across different subnets we need to use multicast addresses, which are in the range through -> D is correct.

Question 3

Question 4

Question 5

Question 6

Question 7

Comments (6) Comments
  1. Patryk
    July 30th, 2017

    Question 1 should be RFC1918? Am I right?

  2. Julian
    August 2nd, 2017

    Which RFC was created to alleviate the depletion of IPv4 public addresses?
    D. RFC 1918

  3. cal24272
    August 4th, 2017

    the answer is D: rfc 1918 — defines private addressing groups, which reduces the need for public addresses. RFC1518 is An Architecture for IP Address Allocation with CIDR

  4. Jack
    August 9th, 2017

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  5. sharkguy
    November 27th, 2017

    @9tut can you confirm question 1? I also agree the 1918 is the correct answer. The ICND1 exam only asks for 1 answer to this question. While both 1518 and 1519 are good choices and do alleviate ip address reduction by creating less waste. The private addressing is what alleviated the addressing by better utilizing Nat.

  6. Anon
    December 21st, 2017

    I’d say Question 1 is definately D. RFC 1918. 9tut?