1
00:00:00,080 --> 00:00:01,170
Okay, so the next step is

2
00:00:01,170 --> 00:00:03,260
to add subnets into our VPC.

3
00:00:03,260 --> 00:00:04,580
So we're going to create two subnets.

4
00:00:04,580 --> 00:00:05,950
One will be a public subnet,

5
00:00:05,950 --> 00:00:07,920
and one will be a private subnet.

6
00:00:07,920 --> 00:00:10,540
Now this is going to be within the one availability zone,

7
00:00:10,540 --> 00:00:13,190
and we'll see what makes a subnet public

8
00:00:13,190 --> 00:00:15,180
or a subnet private.

9
00:00:15,180 --> 00:00:17,610
So let's have a look just first at what subnets are.

10
00:00:17,610 --> 00:00:19,760
So a subnet is going to be, again,

11
00:00:19,760 --> 00:00:23,110
a sub-range of IPv4 addresses within your VPC.

12
00:00:23,110 --> 00:00:25,000
And it turns out that's in this range,

13
00:00:25,000 --> 00:00:27,370
AWS will reserved the five IP addresses in it.

14
00:00:27,370 --> 00:00:30,520
So, the first four IP addresses and the last one is reserved

15
00:00:30,520 --> 00:00:31,740
in each subnet.

16
00:00:31,740 --> 00:00:33,880
These IP addresses are not available for use,

17
00:00:33,880 --> 00:00:37,020
and they cannot be assigned as an IP to an EC2 instance.

18
00:00:37,020 --> 00:00:37,853
So for example,

19
00:00:37,853 --> 00:00:41,320
if you have a CIDR block 10.0.0.0/24,

20
00:00:41,320 --> 00:00:43,700
then you're going to have a few reserved IP addresses.

21
00:00:43,700 --> 00:00:44,890
Such as, well, the first one,

22
00:00:44,890 --> 00:00:46,090
which is network address,

23
00:00:46,090 --> 00:00:46,923
the second one,

24
00:00:46,923 --> 00:00:49,840
so .1, which is reserved AWS for the VPC router,

25
00:00:49,840 --> 00:00:52,440
the .2, which is reserved by AWS for mapping

26
00:00:52,440 --> 00:00:53,820
to Amazon provided DNS,

27
00:00:53,820 --> 00:00:55,397
and this is very important,

28
00:00:55,397 --> 00:00:56,660
.3, which is not used yet,

29
00:00:56,660 --> 00:00:58,870
but is reserved for future use.

30
00:00:58,870 --> 00:01:02,090
And we have .255, which is a network broadcast address.

31
00:01:02,090 --> 00:01:04,950
But because AWS does not support broadcast in a VPC,

32
00:01:04,950 --> 00:01:07,670
this address is reserved and cannot be used, okay?

33
00:01:07,670 --> 00:01:08,760
So as an Exam Tip,

34
00:01:08,760 --> 00:01:11,140
if you need 29 IG IP addresses in a sub-net

35
00:01:11,140 --> 00:01:12,820
for EC2 instances,

36
00:01:12,820 --> 00:01:15,650
then you can not choose a subnet of /27

37
00:01:15,650 --> 00:01:19,490
because this is 32 IP addresses, right, in this /27.

38
00:01:19,490 --> 00:01:21,640
But if you remove the five that are reserved IP addresses,

39
00:01:21,640 --> 00:01:23,280
you're going to get 27 addresses,

40
00:01:23,280 --> 00:01:25,630
which are less than the number 29 that we need.

41
00:01:25,630 --> 00:01:28,210
So we need to choose a subnet size of /26

42
00:01:28,210 --> 00:01:30,630
because this gives us 64 IP addresses in that subnet.

43
00:01:30,630 --> 00:01:33,250
And then if you remove the five reserved IP addresses

44
00:01:33,250 --> 00:01:34,620
with sub-59 IP addresses,

45
00:01:34,620 --> 00:01:37,760
which is greater than the 29 we needed, okay?

46
00:01:37,760 --> 00:01:39,130
So, I will see you in the next lecture

47
00:01:39,130 --> 00:01:40,530
to create our first subnets.