The route for the VPC not showing in iproute2 when a subnet has different mask

Question

I have a VPC with 10.0.0.0/24 network
and a subnet with 10.0.0.0/27 address.

The route table in AWS console shows the default gateway route and 10.0.0.0/24 with target local.
The same routes show in cloud-init log,
but `ip route show` only shows the default gateway and a local route to 10.0.0.0/27.

I tested with Amazon Linux and Debian with the same result.

How do I get a route to 10.0.0.0/24 in the OS?
Is this expected behaviour?

Cheers

Accepted Answer

It is expected behavior. The VPC router (.1 address) will take care of routing across subnets. The OS of the instance will only see a default route to the .1 address.
You should be able to communicate within the VPC (please ensure that Security Groups, NACLs allow appropriate access).

Here's a good landing page for VPC routing:
https://docs.aws.amazon.com/vpc/latest/userguide/VPC_Subnets.html

The route for the VPC not showing in iproute2 when a subnet has different mask

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