can router forward layer 2 frame(without setting destination ip and source ip) written from linux?

router belong to layer 3

why router can send layer 2 frame from computer without knowing destination ip?

Your question is a bit cryptic, but in short: routers don't forward layer 2 frames. Routers forward layer 3 packets, by removing the layer 2 frame information and wrapping it up again in a new frame on the other side.

Systems on the same layer 2 link (ethernet network usually) typically know the ip address of the host (or gateway) they want to communicate with, and then they have to figure out the layer 2 address (MAC) through ARP.

according to your reply,
can a dedicate line from ISP between equity exchange and trading room in another location connected with only switches and not use any routers?

Still confusing.


There a number of ways to route what might be called "non routable" traffic.
Generally one makes a VPN of some type like a GRE tunnel.
One might fool a switch or router to not configure an ip but you'd have to have a dedicate line or tunnel.
There may be some other ways to encapsulate the data in a tcp/ip layer.
One can actually write a driver for odd data.

The level of the switches would determine the possibilities and maybe the type of data. Generally the so call smart switches are really routers. Even commercial switches have options. Soho switches and unmanaged are unlikely to have this ability.

You'd then route traffic to a system to then encapsulate the data and send it.

There are some old protocols too that might be used. Makes the data less secure and difficult to manage.