Creating a synthetic ethernet device eth1: possible?

English Network/Internet
1

Hi,

I’m wondering if it is possible to create a synthetic ethernet device called eth1.
To be clear my system has a physical network card called eth0.
I’ve read howots describing how to create devices tap0, tap1, etc that could be routed through eth0 (the only actual network interface).
Is it a simple case of simply changing the name from tap0 to eth1?
I’m wondering if that won’t break things?

So essentially I have a system with eth0, and would like one that has eth0 and eth1 present.

Appreciate any insights, comments and suggestions

Mark

2

Hi Mark,

Not sure if this helps you but you can create an alias for your existing interface.

This will let you do such things as bind a scondary ip address to the interface.

You can give the alias any name you wish, it will appear as:

eth0:aliasname

when viewed by ifconfig.

You can achieve this manually by editing the interface file under /etc/sysconfig/network and adding the following to the end of the file:

IPADDR_aliasname=‘xxx.xxx.xxx.xxx’
NETMASK_aliasname=‘255.xxx.0.0’
LABEL_aliasname=‘aliasname’

save the file and restart network services

‘rcnetwork restart’

Or you can use to add an alias via Network Devices-Network Card (select your card) -Configure. Aliases setting at the bottom of the screen.

Aliases do require a static ip address.

hth
J

3

Thanks for the suggestion James.
It is a weird situation, but I really need the additional eth1 device.

Mark

4

What is it you are trying to do eventually?

5

Hi Ken,
Eventually I’d like to run some software, that expects two Ethernet devices named eth0 eth1, on a machine that has one.

Mark

6

But software generally expects IP addresses not interfaces, unless you are thinking of firewall software. What kind of software do you have in mind?

You could make an alias interface, and assign it a different address. That can be done in YaST too.

7

The software is along the lines of Rocks cluster stack. During installation it want to interfaces, one to make public and one to treat as private. Would it be possible to make a eth1 that tunneled through eth0. I can see the components, just not if or how they can be used to get a synthetic device.
BTW, to see what I have in mind see the synthetic device in eCOS.

Mark

8

Cluster software, sure, those often require a second interface for communication between cluster members. You could use an alias interface but of course the packets are really using the same physical interface connecting to the same LAN. But you could put them in different VLANs. If there is no problem with time sensitive packets encountering packet delays on the shared LAN, that would be an acceptable solution.

A tunneled device requires a process at both ends to maintain the tunnel, e.g. VPN software. The Linux tap/tun device is designed to be used for such tunneling. It wouldn’t be appropriate for a cluster since you would have to install this extra layer on all participants. Plus there would be more delays in the path.

9

Thanks Ken,
I’ll make an attempt at the alias approach.
Appreciate the feedback and insights.
Mark