1. Mr. Mark Welton

3.  IPv4 address are 32-bit numbers represented in dotted decimal notation of 8 bit segments  00001010.00001000.01100100.00011000  10.8.100.24  So why 8 bit segments?

4.  We started with a classful system (Class A,B,C,etc)  Each class is created by 8-bits of the binary IP  8-bit processing systems where easier and cheaper to build (RFC 791 published in 1981) 110000001010100000000000 Class A Class BClass C

5.  We are accustomed to the decimal system a base 10 system  The number 124 10 is 100+20+4 or ◦ 1x10 2 +2x10 1 +4x10 0 ◦ 1x100+2x10+4x1

6.  The binary number system is a base 2 system  01111100 2 is 0x2 7 +1x2 6 +1x2 5 +1x2 4 +1x2 3 +1x2 2 +0x2 1 +0 x2 0  0x128+1x64+1x32+1x16+1x8+1x4+0x2+ 0x1  64+32+16+8+4 or 124 10

7.  So each octet (8-bit binary number) goes from ◦ 00000000 2 – 111111111 2  So what is the value of 111111111 2

8.  128+64+32+16+8+4+2+1 = 255 10  So what is the hexadecimal value?  8+4+2+1 = 15 or F 16 11111111 1286432168421 2727 2626 2525 2424 23232 2121 2020

9.  IP address allocation is rarely done properly  First mistake I see is people not understand what I just covered  Second mistake I see is not understanding public vs private vs reserved IP addresses  Third mistake I see is not understanding how to take a large prefix and break it down to usable network prefixes that allow for growth  Fourth mistake I see is people not understanding why we do it

10.  We divide the IP space to create segments that makes sense to us  Segmentation = routing  Each IP address allocation is a L2 network which needs a router to move to the next network  The better we do this the easier routing and ACLs are to do  The easier the network is to troubleshoot

11.  RFC 1918 “Address Allocation for Private Internets”  10.0.0.0 – 10.255.255.255 (10/8 prefix)  172.16.0.0 – 172.31.255.255 (172.16/12 prefix)  192.168.0.0 – 192.168.255.255 (192.168/16)  These are the IP address spaces that can be used internally in an enterprise

12.  “link local” block ◦ 169.254.0.0 – 169.254.255.255 (169.254.0.0/16) ◦ To be used when a device can not get an IP address through DHCP  reserves lowest Class B ◦ 128.0.0.0 -128.0.255.255 (128.0.0.0/16) ◦ Not able to be used under old class system but can be assigned to someone now  Also defines loop back space (RFC 1700) ◦ 127.0.0.0 – 127.255.255.255 (127.0.0.0/8) ◦ Used for a machine to communicate internally  Also defines multicast address space (RFC 5771) ◦ 224.0.0.0 – 239.255.255.255 (224.0.0.0/4)  So you should never use these IP address spaces!

13.  Misuse of Public IP address space can cause network routing problems for you network

14.  Prefix 10.0.0.0/8 has what subnet mask?  The 8 says the first 8 bits must be ones  So the first octet would be 255 and all others would be zero  255.0.0.0 11111111 1286432168421

15.  What about 172.16.0.0/16?  192.168.0.0/24?  172.16.0.0/12?

16.  Redefined how a traditionally Classful IP network could be used and subnetted (in equal size block)  With VLSM, subnets can be any size if they follow the binary rules  VLSM allows networks to be subdivided

20. 11000000101010000000000111000000 11111111 11111000 11111111 11110000 11000000101010000000000111001000 192.168.1.192 192.168.1.200 /29 255.255.255.248 /28 255.255.255.240

21.  We use it all the time but do you really know what it is?

22.  CIDR is sort of the inverse of VLSM  Where VLSM prescibes rules for subdividing networks, CIDR prescribes rules for referencing groups of networks with a single route statement  Why would we want to do this?

23. Smaller routing tables are more logical, easier to understand, easier to troubleshoot, and require less CPU and memory for the routers.

24.  IP address allocation is rarely done properly  First mistake I see is people not understand what I just covered Check  Second mistake I see is not understanding public vs private vs reserved IP addresses Check  Third mistake I see is not understanding how to take a large prefix and break it down to usable network prefixes that allow for growth Not Yet  Fourth mistake I see is people not understanding why we do it

25.  Allocate a block of IP addresses that can be referenced with a single access-list (filter) entry  Always allocate more IP addresses than requested

26.  Need 30 IP addresses for a server farm of database servers  Should we use a /27 255.255.255.224?

27.  Need 30 IP addresses for a server farm of database servers  Should we use a /27 255.255.255.224?

28.  Allowing for 30 percent growth is a good rule of thumb  Round up to the next binary boundary  64 IP addresses or a /26 255.255.255.192

29.  Now let say the server farm subnet was already allocated using 10.100.100.0/24  There are currently 10 servers in place .1 for the router and 2-11 for the servers  You need to issue 30 more IP addresses on this subnet  Now what???  Just give them 12-42 right???

31.  Allocating groups of devices into subnettable ranges ◦ allows you to remove them from the network and place them elsewhere without significant changes to the IP network design  You could allocate the range of 32-63 ◦ Access-list 101 permit ip any 10.100.100.32 255.255.255.224 eq web  So we are good right???

32.  You should think ahead and allocate 64 IP addresses on a bit boundary  So you should allocate 64-127  Right??? ◦ Access-list 101 permit ip any 10.100.100.64 255.255.255.192 eq web  Meets both rules so we are good???

34.  IP address allocation is rarely done properly  First mistake I see is people not understand what I just covered Check  Second mistake I see is not understanding public vs private vs reserved IP addresses Check  Third mistake I see is not understanding how to take a large prefix and break it down to usable network prefixes that allow for growth Not Yet  Fourth mistake I see is people not understanding why we do it Know why you are allocating the IP and allow for growth

35.  There are three methods you can use to allocate IP addresses and IP subnets  Sequential– assign the first numerical subnet and then the next and so on, most commonly used. It is easy to understand  Divide by half - every time a network is allocated, the smallest available chunk is divided by half for use while preserving a large portion of IP address space for additional growth  Reverse binary – subnets are allocated by counting in binary with the most and least significant bits reversed. Is the most logical method, but is hard to understand

37.  Some of us have been doing this for so long we remember the rule of all-zeros and all- ones as it relates to subnets  RFC 1878 states, “This practice  (of excluding all-zeros and all-ones subnets) is obsolete. Modern software will be able to  utilize all definable networks.”  Sometimes you maybe in an environment where legacy equipment can not do this  Or the staff still think they have to follow the rule

41.  For the Cisco people in the class. You will need to know Cisco’s way to pass the CCNA  or know how to get the answer to the question based on how Cisco or vendor X tests  Everyone knows (or should now) that two IP addresses are used in every subnet (one for the gateway and one for broadcast)  Unless you have done enough networking to know you can use a /31 for to routers in a point-to-point connection. DO NOT ASKING IF YOU ARE NOT GOING TO TAKE CCDP!!!

42.  A /24 subnet has 256 host IP addresses – 254 IP are usable by host devices  Everything is based on the subnet masks which is based on binary  Everything will be powers of 2 and will either produce 256 or be divisible by 256  The maximum value of an octet is 255 (but remember we count from 0 so 256 number)

43.  Subnet masks are, by their nature, inclusive  There are only nine values that are possible for any octet in a subnet mask

45.  What the author is trying to say is a /24 or 255.255.255.0 would have 256 host with 16,777,216 possible subets (256*256*256*1)

46.  I find an expanded for of the horizontal format very useful Increment Number of hosts 1286432168421 CIDR/25/26/27/28/29/30/31/32 mask128192224240248252254255 Usable Hosts 12662301462--