Lecture 14: Default VPC
- 课程：[NEW] AWS Certified Advanced Networking Specialty 2026
- 视频时长：05:34
- 来源：Udemy Lecture 24112456
- Slide 数量：3
- 画面切换：约 03:52、05:08
扫描说明
按页面英文 transcript 的 112 个时间点逐一定位并检查视频画面。默认 VPC 架构图中的子网、路由和说明文字逐步出现均合并为同一小节；AWS 控制台演示作为独立小节；返回讲义后的删除与重建说明单列一节。
Transcript 来自 Udemy 页面自带的英文自动字幕，没有使用 ASR。下面保留页面原文，包括其中的语法或识别错误。
1. Default VPC Architecture
时间范围：00:00–03:52
总结 / Summary
中文
每个 AWS 区域（AWS Region）默认创建一个默认 VPC（Default VPC），用于快速启动 EC2 实例。它使用 172.31.0.0/16 CIDR，在每个可用区（Availability Zone, AZ）创建一个 /20 公有子网（public subnet），附加互联网网关（Internet Gateway, IGW），并在主路由表（main route table）中加入互联网默认路由。每个 /20 子网包含 4,096 个 IPv4 地址，其中扣除 AWS 保留的 5 个地址后有 4,091 个可供资源使用。生产环境通常更适合使用自行设计的自定义 VPC（custom VPC）。
English
Every AWS Region includes a Default VPC for quickly launching EC2 instances. It uses the 172.31.0.0/16 CIDR, creates one /20 public subnet in each Availability Zone, attaches an Internet Gateway (IGW), and adds an Internet default route to the main route table. Each /20 subnet contains 4,096 IPv4 addresses, of which 4,091 remain after AWS reserves five. Production environments generally benefit from purpose-built custom VPCs.
Transcript
00:00 Hello and welcome to this lecture,
00:02 default VPC.
00:03 So, so far we saw custom VPCs typically,
00:06 we understood how the VPC, route table, subnets,
00:09 everything works, but if you have ever tried
00:12 to launch an EC2 instance,
00:14 by default, it won't ask you to set up the network
00:18 or anything that's because of for our convenience,
00:23 every AWS region has one default VPC created by default.
00:29 And when you launch your first EC2 instance,
00:31 it gets deployed into that particular VPC,
00:35 into one of the subnets inside that VPC,
00:38 and then you can access your EC2 instance over internet
00:41 and you connect to it.
00:43 So this all happens because there is something
00:45 called a default VPC,
00:47 and there is nothing special about this VPC per se.
00:50 That means you can anytime go and delete this VPC,
00:53 but for making it easier,
00:56 this default VPC is created in every region for you.
00:59 So let's look at how the default VPC looks like
01:03 so that we know why certain things are working,
01:06 why certain things are not working
01:08 in case you are deploying everything into the default VPC.
01:11 However, it is highly recommended
01:13 that you always use your own VPC
01:16 and you manage your routes and gateways yourself.
01:19 Default VPC is probably for the quick access
01:22 to launching EC2 instance like that.
01:25 So as you can see here in the diagram,
01:28 every region would have a VPC
01:31 and this VPC would typically have
01:34 one subnet per availability zone,
01:36 because subnet and availability zone
01:38 is like one-to-one relation.
01:42 At least one subnet cannot be in AZs, right?
01:45 So if you want to have your EC2 instance in any of the AZ,
01:49 that means you need a sub-net in that AZ.
01:50 And that's your default VPC
01:51 create as many AZ as those mini subnets are created.
01:55 So in Mumbai, there are three AZs as of today.
01:58 And that's why you see there are three subnets
02:01 created for you automatically as a part of default VPC.
02:05 If you are talking about Sinatra, Virginia,
02:07 there are six availability zones,
02:09 and that's why there will be six public subnets.
02:13 Now the other thing is the CIDR ranges constant
02:15 across all the regions.
02:17 As this is a private IP address range,
02:19 you can very well have the same range
02:21 anywhere in any region.
02:23 So the range it takes is 172.31.00/16.
02:29 Now, let's talk about the route tables
02:32 and internet connectivity.
02:33 This default VPC comes with a single internet gateway,
02:37 and instead of creating an individual route table
02:40 for every subnet, there is already a route
02:43 in the main route table for the internet gateway,
02:46 which means all these subnets will follow
02:49 this main route table by default,
02:51 and they become the public subnet
02:54 because there is a route for internet gateway
02:58 and all subnets follow the same rules.
03:01 So this is how the default VPC looks like.
03:04 Let's go over the properties again.
03:06 Every region has a default VPC.
03:09 Yeah, it has this fixed CIDR.
03:12 Then there is a subnet in every AZ.
03:16 The subnet ranges /20.
03:18 That means two raised to 12 IP addresses,
03:20 that is 4096 IP addresses in every subnet
03:24 and usable will be 4091 as five IPs are reserved.
03:30 Further, it also creates internet gateway
03:32 and it adds a route table.
03:36 Actually it adds a rule to the main route table
03:39 with this IGW, with the destination as internet IP address.
03:45 So that's what makes the default VPC.
03:48 Just let's look at the actual default VPC.
2. Default VPC in the AWS Console
时间范围：03:52–05:08
总结 / Summary
中文
AWS 控制台（AWS Console）可显示 VPC 是否为默认 VPC、其三个子网 CIDR、主路由表（main route table）以及指向互联网网关（Internet Gateway）的路由。控制台演示验证了默认 VPC 的公有子网、路由表和互联网连接均由 AWS 自动配置。
English
The AWS Console shows whether a VPC is the default, its subnet CIDRs, main route table, and route to the Internet Gateway. The demonstration confirms that AWS automatically configures the public subnets, routing, and Internet connectivity of a Default VPC.
Transcript
03:52 Now, if you look at this, my console,
03:55 I'm in the Mumbai region and currently I have two VPCs
03:58 out of which, the shorter ID is the default VPC.
04:04 And you can look at its properties like it says here,
04:06 the default VPC is, yes, right?
04:09 And if you look at the subnets,
04:13 this VPC has this three subnets
04:16 and the CIDR is 172.31.0.0/20,
04:21 and subsequently for the other subnets as well.
04:24 Now let's look at the route table, as I said.
04:27 So this VPC has one main route table, which is this.
04:30 You can look at the tag as main as yes here.
04:34 And if you look at the routes now,
04:36 it has this route for internet traffic.
04:39 So this eventually makes the default VPC.
04:43 Now many are times by accidentally,
04:45 you may delete the default VPC,
04:47 or if you want to recreate the default VPC, you can do that.
04:50 You can just go here on the VPC console to your VPCs
04:54 and through actions, you can say, create a default VPC.
04:57 Right now I already have a default VPC,
05:01 and that's why the option is disable.
05:04 So that's about the default VPC.
3. Recreating a Deleted Default VPC
时间范围：05:08–05:34
总结 / Summary
中文
默认 VPC（Default VPC）并无特殊的网络行为，也可以被删除。如果误删或需要恢复，可以在 VPC 控制台的“Your VPCs → Actions → Create default VPC”中重新创建。重新创建后仍适用普通 VPC 的 CIDR、子网、路由和网关原理。
English
A Default VPC has no special networking behavior and can be deleted. If it is removed accidentally or needs to be restored, it can be recreated from Your VPCs → Actions → Create default VPC in the VPC console. The same CIDR, subnet, routing, and gateway principles used by ordinary VPCs continue to apply.
Transcript
05:07 Just more thing about default VPC is that if deleted,
05:10 you can recreate it from your VPC's action
05:14 and create default VPC.
05:16 So as of now, this is what you need to know
05:18 about the default VPC.
05:19 So don't worry if it gets deleted, you can recreate it,
05:22 and there is nothing magical about it.
05:24 Everything that we learned applies
05:27 to the default VPC as well.
05:29 So that's it about it and stay tuned for the next lectures.
05:33 Thank you.
整讲总结 / Overall Summary
中文
默认 VPC（Default VPC）是 AWS 在每个区域中预先创建的便捷网络：它包含 172.31.0.0/16 地址空间、每个可用区一个 /20 公有子网（public subnet）、互联网网关（Internet Gateway）以及带互联网路由的主路由表（main route table）。它适合快速实验，但自定义 VPC（custom VPC）能提供更明确的地址、路由和安全控制。默认 VPC 被删除后可从 VPC 控制台重新创建。
English
A Default VPC is a convenience network pre-created by AWS in each Region. It includes the 172.31.0.0/16 address space, one /20 public subnet per Availability Zone, an Internet Gateway, and a main route table with an Internet route. It is useful for quick experimentation, while custom VPCs provide clearer control over addressing, routing, and security. A deleted Default VPC can be recreated from the VPC console.
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