关于VPC中routes的含义及Next Hop列“Virtual network default”的场景化通俗解释咨询

Hey there! Let's unpack these VPC routing questions with straightforward examples—no jargon overload, promise.

Think of your VPC as a private, fenced-off office campus with multiple buildings (subnets) and different entry/exit points (gateways). Routes are like the customizable road signs placed all around this campus. Each route entry is a simple rule:

• "If you're headed to [specific address range], take this path to [next destination]."

For example:

• A route might tell traffic bound for another subnet in the same VPC to go to the local subnet gateway.
• Another route could direct internet-bound traffic to a NAT gateway or internet gateway.
• Routes even handle traffic going to on-premises networks via a VPN or direct connect.

They’re the backbone that ensures your data packets don’t get lost wandering around the VPC—they always know the right way to their target.

Great question—let’s tie this directly to the scenario you described: "数据包离开VM后到达自身子网的网关，网关随后将其转发至下一个子网" (After a packet leaves a VM, it reaches its own subnet gateway, which then forwards it to another subnet).

First, "Virtual network default" is an auto-generated default route that comes with every VPC. It’s pre-configured to handle all traffic within your VPC’s entire address range (its CIDR block). Here’s how it works in your scenario:

Let’s say your VPC has two subnets:

• Subnet A: 10.0.1.0/24 (with a VM at 10.0.1.5)
• Subnet B: 10.0.2.0/24 (with a VM at 10.0.2.8)
• VPC CIDR: 10.0.0.0/16 (covers both subnets)

1. The VM in Subnet A sends a packet to 10.0.2.8. Since the target is within the VPC’s CIDR, the VM sends the packet to Subnet A’s gateway first.
2. The gateway checks its route table and sees the "Virtual network default" entry. This entry says: "For any traffic headed to the 10.0.0.0/16 range (our entire VPC), use the VPC’s internal routing system as the next hop."
3. That "Virtual network default" is essentially the VPC’s built-in "internal navigation system." It knows exactly how to forward the packet from Subnet A’s gateway to Subnet B’s gateway, and finally to the target VM at 10.0.2.8.

The "default" part means you don’t have to create this route manually—it’s there from the moment you spin up the VPC, handling all internal subnet-to-subnet communication automatically. It’s like the campus’s default internal road network: you don’t have to map out how to get from Building A to Building B— the pre-existing roads (default route) take care of it.

内容的提问来源于stack exchange，提问作者D.B.K