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MarcusW
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Same network on different interfaces

Thu Nov 15, 2012 11:35 pm

I have been struggling for three days now trying to make this setup working:

I want every interface on the router to be on the same network, for example ether1 10.0.1.1/24 and ether2 10.0.1.2/24. I want to do it this way to be able to set a dhcp-server on every interface and set a one specific IP-address on that interface so that connecting something to for example ether1 always gives and IP-address to the client of 10.0.1.100 and for ether2 10.0.1.101. To be able to have it this way I have added proxy-arp to the interfaces so that the clients can reach each other and sometimes this works for a while.. After a reboot it usually don't.

I have reed this text in the wiki:
Two IP addresses from the same network assigned to routers different interfaces are not valid unless VRF is used. For example, the combination of IP address 10.0.0.1/24 on the ether1 interface and IP address 10.0.0.132/24 on the ether2 interface is invalid, because both addresses belong to the same network 10.0.0.0/24. Use addresses from different networks on different interfaces, or enable proxy-arp on ether1 or ether2.

I have tried to have proxy-arp activated on both interfaces and just one but nothing works reliable. Should I use it on both our just one and can I use it on both?
I manage to get it working with VRF but just for a short while..

I need some advice.. Anyone?
 
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Re: Same network on different interfaces

Fri Nov 16, 2012 11:47 am

Somebody could spend a while going through all this with you, but there are better ways of doing things - what you are trying is definitely non-standard!

Do you mind if I ask why you want to use the same address space over all the interfaces and why you can't do it any other way?
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MarcusW
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Re: Same network on different interfaces

Fri Nov 16, 2012 2:07 pm

Somebody could spend a while going through all this with you, but there are better ways of doing things - what you are trying is definitely non-standard!

Do you mind if I ask why you want to use the same address space over all the interfaces and why you can't do it any other way?
No not at all. This is the case I'm working on:

We have small embedded systems that we want to connect to preconfigured routers so that they can start to communicate internally behind the router but even be possible to reach from the outside. To share data between them they are preconfigured to try to talk with devices having predefined IP-addresses and depending on wich IP they have they also have different functions to do. Example: If a system gets IP 10.0.1.100 because it's connected to ether1 then that system/device is the master and if it can reach 10.0.1.101 then it has a slave who has specific tasks to do. The router should then be marked so that it's easy to connect different systems to the correct ethernet port(depending on the functions you want). It's the same program in every system but they change function dependning on where they are located on the router. Up to this point it would be easy just to let the router route the traffic and instead use different IP series ether1 10.0.1.100 ether2 10.0.2.100 and so on. But it should also be easy to attach a computer to the last port in the router and in that port get access to internet and also all systems. It should be plug and play so everything is done by DHCP and they can easy access the systems. The problem now is that many of these computers also has vpn and other connections active and usually another default route then the router gives it with DHCP. And because every system is on a different subnet it's not possible to reach from that computer having another default route. We could send more routes with DHCP to the computers but it would be more pedagogic that every system was on the same subnet and also not every DHCP client handle the extra routes sent.

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