---
title: "Cross Subnet Communication"
description: "Let instances in different Subnets of an Exoscale VPC communicate by routing VPC traffic through the VPC interface in the operating system."
url: https://community.exoscale.com/product/networking/vpc/how-to/cross-subnet-communication/
product: "VPC"
section: product
last_updated: 2026-10-26
---
> For AI agents: the documentation index is at https://community.exoscale.com/llms.txt. Every page is available as markdown at `<page URL>index.md` or with `Accept: text/markdown`.

# Cross Subnet Communication

Two instances in the same VPC but in different subnets can communicate by default, thanks to the
VPC routes created along with each subnet (see
[Using Routing Rules](https://community.exoscale.com/product/networking/vpc/how-to/using-routing-rules/index.md)), as long
as the Security Group rules allow this traffic.

However, due to a current limitation of the VPC product, this requires a small configuration inside
the operating system of your instances: packets destined for the VPC must leave through a VPC
interface, not through the public interface.

For example if you have `instance-A` in the subnet `10.1.0.0/16` and `instance-B` in the subnet
`10.2.0.0/16`, you need to run the following commands:

```console
ubuntu@instance-A:~$ sudo ip route add 10.2.0.0/16 via 10.1.0.1 dev eth1
```

```console
ubuntu@instance-B:~$ sudo ip route add 10.1.0.0/16 via 10.2.0.1 dev eth1
```

To simplify the configuration on the instance as much as possible, you could set a route for any
CIDR that contains the subnet, potentially using a CIDR that contains all your subnets so a single
route is enough rather than one per subnet.

Moreover, if you have different VPC interfaces in your instance, you can use any as the target of
this routing rule.


> [!NOTE]
> Add the following route to all instances that need cross-subnet communication
> ```console
> ubuntu@instance-X:~$ GW=$(ip route show dev eth1 scope link | awk '{print $1; exit}')
> ubuntu@instance-X:~$ sudo ip route add <CIDR_THAT_CONTAINS_ALL_SUBNETS> via $GW dev eth1
> ```