Routes and Route Tables – AWS vs GCP

What is a Route?

A route is an instruction for directing traffic.  It is applied to an entire set of IP addresses – typically to an entire VPC or a subnet within the VPC.

DESTINATION refers to the set of IP addresses and TARGET refers to where to point the traffic to.

For example, if the destination is the internal IPs of a subnet, the TARGET is LOCAL (local covers all internal IP addressing).

The route table works the same way in GCP – instead of TARGET, the term used is NEXT HOP.

AWS Route Tables

While there is one main route table, each subnet can be associated with it’s own custom route table.

So – say you have 2 subnets – A and B. To start out, both A and B inherit the main routing table. Now, you can define a separate routing table for Subnet B – and associate that with B. Only A uses the main routing table – and B uses it’s new custom routing table.

If your new custom routing table looks better to you, you can convert it to the main route table. This will make subnet A also use this new table since it is now the MAIN route table (The older main route table is no longer in use – since both A and B are using the new route table).

GCP Route Tables

As opposed to this, on GCP, there is only ONE global routing table. This is because there is no need to create routes between regions (your subnet automatically spans all regions).

As long as your subnets use non overlapping, distinct address spaces, you can address VMs in subnets without using custom routes (i.e. just using their internal IP addresses). You can even connect on premises networks to the Google cloud network by using VPC tunnels – and creating a route entry that points to the VPN tunnel.

Summary

Routing is considerably simplified in Google Cloud due to the global nature of network (VPCs, Subnets span across regions). Custom Routes CAN still be defined -and are typically used to create routes between appliances (e.g. firewall appliances deployed on Google Cloud)