IPv4 uses 32-bit numbers that combine a network and a host address. IP addresses are written in four dotted decimal fields. Each number represents a byte (meaning 192 would be a byte cause in decimal its actually made up of 8 bits). The far left bits are the network address because all hosts on this network have addresses that start with that pattern, the right bits are host addresses and each host has a different value.
Resources for IP address Internetworking Technology Handbook: Internet Protocol
Binary Review
IP Addresses are composed of four bytes (8 bits) and in networking binary works one bit at a time from 0000 0000 to 1111 1111 (0 to 2555) IRL networking that’s what you need to know (test are different cause they ask more than just 255). This is a CCNA topic and I filled note pads with examples just to be able to get it as natural as quick as possible, after a while you start remembering 1010 1100 (172) and 1100 0000 (192). The old CCNA Prep Centre (now Cisco Learning Network) had a Java based game to get this into your head where you had to convert Binary to Decimal against the clock. Helped me because its repetition, repetition, repetition.
Classfull Network Ranges
The above network address (192.168.16.2) at the top of the post starts with 192.xxx.xxx.xxx if you didnt have this table to the right here are the steps to find out which network it belongs to.
Step 1: Converting the first byte to binary 1100 0000 (192).
Step 2: You take the first 4 bits and compare them to what you know:
- Class A starts with 0,
- Class B starts with 10, and
- Class C starts with 110.
This means that the address is a Class C address.
This is something that you must just know, get to know the first column and associate that column with the Class on the table above and then the you can figure out the range easily enough (if you are good with memorizing tables just memorize the bits, range and class).
Network Range by Subnet Masks
Subnetting is when you take the assigned network and break it into smaller pieces this can be useful to conserve IP address space (or when I was doing the CCNA I did this to practice on my office network). The book I am using (Brent D. Stewart, CCNP BSCI Official Exam Certification Guide; Fourth Ed.) uses a Truth Table for AND that is really easy to use and master.
Another method would be to use a table, its also not rocket science but means that you don’t actually know how to do this on the fly.
Moving along lets use the AND method and an example. What network does PC 3 belong to with the IP 192.168.5.100 and the subnet mask 255.255.255.224 and what are the usable addresses on this network.
STEP 1: If the mask is given in decimal notation, convert it to CIDR notation (maybe a long way but you going to need the binary in a second anyway).
STEP 2: To determine the network address of the IP address, copy the network bits from the address as shown by the CIDR notation. Fill in the remaining bits with zeros.
STEP 3: The last Address in the range is the broadcast address. To find this out do the following:
STEP 4: The usable network addresses fall between STEP 2 and STEP 3.
STEP 5:To check this subtract the CIDR notation from 32 that’s 32 – 27 (not the other way around cause you going to get a negative number). To determine the “amount” of addresses then plug it into this formula 2n-2 (n = number of host bits).
Resources for Subnet Mask and Classes: Internetworking Technology Handbook IP Address Classes
Summarization
Summarization (route summarization) is a technique used to group IP networks together to minimize IP advertisements. Doing this allows one to hide unimportant details (flapping links) and to simplify the routing process (make better use of router CPU and memory than to process and store routing information). One of the keys to scalable routing is to take large complicated sets of advertisements and reduce them as much as possible (think internet).
Step 1: Write each network in binary
Step 2: Determine the number of bits that match. This gives a single summary that includes all the routes, but may include a range of addresses that is too large (over-summarization)
Step 3: If step 2 unacceptably over-summarizes, start from the first address and add bits to the prefix until a portion of the range is summarizes. Take the remaining addresses and start this process again.
Step 4: Write each network in binary
Step 5: Determine the number of bits that match.
Step 6: Because step 2 did not over-summarize, the process is complete. Answer is 192.168.0.0/21 and 192.168.0.0/23
Address Planning
Summarization is not possible if network numbers are randomly assigned within an organization. When designing a network it is important to keep in mind the requirements for summarization.
Notes and Notices:
This is a part of my personal BSCI notes and research to assist myself in learning and understanding the concepts and theory for the BSCI exam. I learn by making notes reading and writing things down and wish to file them where I can’t lose them. These notes are not to be seen, judged or mistaken for replacements to Cisco recognized and authorized training which I personally support and attend and suggest you undertake if you are going for the BSCI Certification.
