Creating a virtual IP to route packets through a specific interface

kevmo314

12/30/22, 5:07 PM

I have a server with ip 34.0.0.0 and multiple network devices, each corresponding to a local ip address 192.168.42.1, 192.168.42.2, 192.168.42.3, etc.

I'd like to be able to create a local tunnel through each of these interfaces so that traffic is routed through the corresponding local interface. For example, I'd like to create 192.168.72.1 that routes traffic through 192.168.42.1 to 34.0.0.0. Is this possible?

I know that with multiple destination ip addresses I can selectively route packets through each of the interfaces with iptables but I'm not sure now to create a local tunnel. My server has only one ip address and I'd like to do this purely on the client. Additionally, I don't have control over the sending code so I cannot selectively bind the sockets to each local IP but I can change the target IP that the packets are sent to.

EDIT: After some more digging it seems what I'd like to do is mark a packet as it goes through the OUTPUT chain of iptables and use this to inform the routing decision? Is there an easier way than this? It seems that the packet destination can't be changed after the routing decision is made.

0 + 3

iptables

Nikita Kipriyanov

12/31/22, 5:14 PM

You need to use routing policy database. Please read LARTC, its purpose is exactly to answer questions like this. And no, you don't need any tunnels or additional IPs, you need additional *routing tables* and *routing rules*.

kevmo314

12/31/22, 8:41 PM

@NikitaKipriyanov can you point me to where in LARTC it describes how to do this? Everything I have seen describes how to split packets with different destination IPs, but not how to split packets with the same destination IP by rewriting the destination IP...

Nikita Kipriyanov

1/1/23, 2:03 PM

I don't see anything in your quesiton that signifies a different *destination* translation should be done for different packets (and what is the selector). Could you please clarify the task then, by submitting an example of how in the end packets (ideally) should be processed, instead of suggesting an assumed solution (tunnel)? Say, hat, packets from A to M must arrive to X, packets from B to M must arrive to Y, or something like that.

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: Creating a virtual IP to route packets through a specific interface

TH: การสร้าง IP เสมือนเพื่อกำหนดเส้นทางแพ็กเก็ตผ่านอินเทอร์เฟซเฉพาะ

RO: Crearea unui IP virtual pentru a ruta pachetele printr-o interfață specifică

RU: Создание виртуального IP для маршрутизации пакетов через определенный интерфейс

VI: Tạo một IP ảo để định tuyến các gói thông qua một giao diện cụ thể

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