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Q&A Access host device which bridges a connected device through same eth interface

I got 2 small computers running Linux. One acts as ethernet gadget, connected via USB to the other, the host. I set up a bridge, like so: ip link add name br0 type bridge ip link set dev br0 up...

1 answer · posted 2y ago by sktpin‭ · last activity 2y ago by sktpin‭

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#4: Post edited by

sktpin‭ · 2021-08-11T10:16:52Z (over 2 years ago)

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I got 2 small computers running Linux.
One acts as ethernet gadget, connected via USB to the other, the host.
I set up a bridge, like so:
```
ip link add name br0 type bridge
ip link set dev br0 up
ip link set dev eth0 master br0
ip link set dev usb0 master br0
```
On the gadget, its usb0 interface has 2 IP addresses: the one in the 169.... net that the host also has on its usb0, which I consider the "internal" connection/subnet between the two computers - and the second IP on the gadget is one in the "outside" subnet, which the bridging host is connected to with its eth0 interface.
This almost works. Except, when I run the script that sets up the bridge, I cannot connect to the host anymore, e.g. SSH into it with its eth0's own IP address.
**Edit**: What's weird is that establishing SSH connections to the host eth0's own IP still **works for a while** (e.g. tens of seconds) after setting up the bridge, but ceases to work then.
I found [something here](https://docs.openvswitch.org/en/latest/faq/issues/), indicating that, if eth0 has a bridge to something else, it's not supposed to have an own IP address. The text suggests to add an address to the bridge:
```
ip addr flush dev eth0
ip addr add 192.168.128.5/24 dev br0
ip link set br0 up
```
That didn't help, though.
The goal is to be able to access both from the outside world (a local network with a bunch more computers), with all thinkable protocols: the host device, as well as the gadget, and bridging seemed like the way.
How is this done correctly?

I got 2 small computers running Linux.
One acts as ethernet gadget, connected via USB to the other, the host.
I set up a bridge, like so:
```
ip link add name br0 type bridge
ip link set dev br0 up
ip link set dev eth0 master br0
ip link set dev usb0 master br0
```
On the gadget, its usb0 interface has 2 IP addresses: the one in the 169.... net that the host also has on its usb0, which I consider the "internal" connection/subnet between the two computers - and the second IP on the gadget is one in the "outside" subnet, which the bridging host is connected to with its eth0 interface.
This almost works. Except, when I run the script that sets up the bridge, I cannot connect to the host anymore, e.g. SSH into it with its eth0's own IP address.
**Edit**: What's weird is that establishing SSH connections to the host eth0's own IP still **works for a while** (e.g. a few minutes) after setting up the bridge, but ceases to work then.
I found [something here](https://docs.openvswitch.org/en/latest/faq/issues/), indicating that, if eth0 has a bridge to something else, it's not supposed to have an own IP address. The text suggests to add an address to the bridge:
```
ip addr flush dev eth0
ip addr add 192.168.128.5/24 dev br0
ip link set br0 up
```
That didn't help, though.
The goal is to be able to access both from the outside world (a local network with a bunch more computers), with all thinkable protocols: the host device, as well as the gadget, and bridging seemed like the way.
How is this done correctly?

#3: Post edited by

sktpin‭ · 2021-08-11T10:08:14Z (over 2 years ago)

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I got 2 small computers running Linux.
One acts as ethernet gadget, connected via USB to the other, the host.
I set up a bridge, like so:
```
ip link add name br0 type bridge
ip link set dev br0 up
ip link set dev eth0 master br0
ip link set dev usb0 master br0
```
On the gadget, its usb0 interface has 2 IP addresses: the one in the 169.... net that the host also has on its usb0, which I consider the "internal" connection/subnet between the two computers - and the second IP on the gadget is one in the "outside" subnet, which the bridging host is connected to with its eth0 interface.
This almost works. Except, when I run the script that sets up the bridge, I cannot connect to the host anymore, e.g. SSH into it with its eth0's own IP address.
I found [something here](https://docs.openvswitch.org/en/latest/faq/issues/), indicating that, if eth0 has a bridge to something else, it's not supposed to have an own IP address. The text suggests to add an address to the bridge:
```
ip addr flush dev eth0
ip addr add 192.168.128.5/24 dev br0
ip link set br0 up
```
That didn't help, though.
The goal is to be able to access both from the outside world (a local network with a bunch more computers), with all thinkable protocols: the host device, as well as the gadget, and bridging seemed like the way.
How is this done correctly?

I got 2 small computers running Linux.
One acts as ethernet gadget, connected via USB to the other, the host.
I set up a bridge, like so:
```
ip link add name br0 type bridge
ip link set dev br0 up
ip link set dev eth0 master br0
ip link set dev usb0 master br0
```
On the gadget, its usb0 interface has 2 IP addresses: the one in the 169.... net that the host also has on its usb0, which I consider the "internal" connection/subnet between the two computers - and the second IP on the gadget is one in the "outside" subnet, which the bridging host is connected to with its eth0 interface.
This almost works. Except, when I run the script that sets up the bridge, I cannot connect to the host anymore, e.g. SSH into it with its eth0's own IP address.
**Edit**: What's weird is that establishing SSH connections to the host eth0's own IP still **works for a while** (e.g. tens of seconds) after setting up the bridge, but ceases to work then.
I found [something here](https://docs.openvswitch.org/en/latest/faq/issues/), indicating that, if eth0 has a bridge to something else, it's not supposed to have an own IP address. The text suggests to add an address to the bridge:
```
ip addr flush dev eth0
ip addr add 192.168.128.5/24 dev br0
ip link set br0 up
```
That didn't help, though.
The goal is to be able to access both from the outside world (a local network with a bunch more computers), with all thinkable protocols: the host device, as well as the gadget, and bridging seemed like the way.
How is this done correctly?

#2: Post edited by

sktpin‭ · 2021-08-10T17:23:00Z (over 2 years ago)

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I got 2 small computers running Linux.
One acts as ethernet gadget, connected via USB to the other, the host.
I set up a bridge, like so:
```
ip link add name br0 type bridge
ip link set dev br0 up
ip link set dev eth0 master br0
ip link set dev usb0 master br0
```
On the gadget, its usb0 interface has 2 IP addresses: the one in the 169.... net that the host also has on its usb0, which I consider the "internal" connection/subnet between the two computers - and the second IP on the gadget is one in the "outside" subnet, which the bridging host is connected to with its eth0 interface.
This almost works. Except, when I run the script that sets up the bridge, I cannot connect to the host anymore, e.g. SSH into it with its eth0's own IP address.
I found [something here](https://docs.openvswitch.org/en/latest/faq/issues/), indicating that, if eth0 has a bridge to something else, it's not supposed to have an own IP addres. The text suggests to add an address to the bridge:
```
ip addr flush dev eth0
ip addr add 192.168.128.5/24 dev br0
ip link set br0 up
```
That didn't help, though.
The goal is to be able to access both from the outside world (a local network with a bunch more computers), with all thinkable protocols: the host device, as well as the gadget, and bridging seemed like the way.
How is this done correctly?

I got 2 small computers running Linux.
One acts as ethernet gadget, connected via USB to the other, the host.
I set up a bridge, like so:
```
ip link add name br0 type bridge
ip link set dev br0 up
ip link set dev eth0 master br0
ip link set dev usb0 master br0
```
On the gadget, its usb0 interface has 2 IP addresses: the one in the 169.... net that the host also has on its usb0, which I consider the "internal" connection/subnet between the two computers - and the second IP on the gadget is one in the "outside" subnet, which the bridging host is connected to with its eth0 interface.
This almost works. Except, when I run the script that sets up the bridge, I cannot connect to the host anymore, e.g. SSH into it with its eth0's own IP address.
I found [something here](https://docs.openvswitch.org/en/latest/faq/issues/), indicating that, if eth0 has a bridge to something else, it's not supposed to have an own IP address. The text suggests to add an address to the bridge:
```
ip addr flush dev eth0
ip addr add 192.168.128.5/24 dev br0
ip link set br0 up
```
That didn't help, though.
The goal is to be able to access both from the outside world (a local network with a bunch more computers), with all thinkable protocols: the host device, as well as the gadget, and bridging seemed like the way.
How is this done correctly?

#1: Initial revision by

sktpin‭ · 2021-08-10T17:22:15Z (over 2 years ago)

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Access host device which bridges a connected device through same eth interface

I got 2 small computers running Linux.
One acts as ethernet gadget, connected via USB to the other, the host.

I set up a bridge, like so:

```
ip link add name br0 type bridge
ip link set dev br0 up
ip link set dev eth0 master br0
ip link set dev usb0 master br0
```

On the gadget, its usb0 interface has 2 IP addresses: the one in the 169.... net that the host also has on its usb0, which I consider the "internal" connection/subnet between the two computers - and the second IP on the gadget is one in the "outside" subnet, which the bridging host is connected to with its eth0 interface.

This almost works. Except, when I run the script that sets up the bridge, I cannot connect to the host anymore, e.g. SSH into it with its eth0's own IP address.

I found [something here](https://docs.openvswitch.org/en/latest/faq/issues/), indicating that, if eth0 has a bridge to something else, it's not supposed to have an own IP addres. The text suggests to add an address to the bridge:

```
ip addr flush dev eth0
ip addr add 192.168.128.5/24 dev br0
ip link set br0 up
```

That didn't help, though.

The goal is to be able to access both from the outside world (a local network with a bunch more computers), with all thinkable protocols: the host device, as well as the gadget, and bridging seemed like the way.

How is this done correctly?

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