Sending and receiving packets without being connected

I dont want to connect them.

I'd have to agree with @rj-45 ...please more clearly explain what you mean by "not connected."

I know of no way to send a packet from D1 (connected to R1) to D2 (connected to R2), unless R1 and R2 are connected in some manner.

If there is no connection between the hosts, there is no magic in IP or Ethernet addresses alone that can convey the packets from one to another, routers or not.

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This really doesn't make much sense. Are the two systems L1-R1 and L2-R2 in different facilities, each connected to the Internet through separate connections? In that case you could set up a VPN between them.

You never ever want the same MAC address on two devices that are both active on a network at the same time. And you almost never want the same IP address.

When D1 sends a packet to R1, R1 looks at its routing table.

So if D1 sends to 192.168.1.105 which is D2. R1 on receiving this looks at routing. Check this with ip route, e.g. what I have:

192.168.1.0/24 dev wlp3s0 proto kernel scope link src 192.168.1.187

So if you had something like this on R1, then R1 would send 192.168.1.105 out on the wlp3s0 port, as that is where that sub net lives.

No if D2 isn't on the wlp3s0 net, it won't get the packet ...

So check your routes ....

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we should wait for the detailed explanation, everything else is just a wild guess.

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It cannot communicate directly. It has to go through the router. Now the router has openwrt installed. I hardcoded the ip and mac of D2 in openwrt. So if D1 creates an ethernet packet now, it should have the MAC of the R1.
R1 accepts the packet. It finds the destination IP of D2. It then checks the ARP table, it should find the matching IP of D2 and its corresponding MAC. It should again make an ethernet packet with D2s MAC and puts it on air.

Now here is my question. Will D2 receives this signal? Does the packet reach D2.

Not without static routes, as described in Post #19 above

Whoa! On air!?!?

  • Are you connecting R1 and R2 via Wireless???
  • If so, why don't you make a static route?
  • From your description, R1 wouldn't find the MAC of D2, it should find the MAC of R2. Configuring R1 to broadcast to D2 is INCORRECT.
  • R1 would not put a packet on air with the MAC of D2, this is false - unless everything is on the same subnet, and therefore the same broadcast domain, and IP subnet. Otherwise, you must use routers, and therefore, add static routes to R1 and R2.

I think we need die picture/diagramm of all the devices!

Why do you give us so little information about the two routers? Is there a cable between them or do the use wifi?

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R1 and R2 are not connected via wireless or wire.

Why R1 wouldnt find the MAC of D2?
Correct me if I am wrong.
In ARP table of the R1 I have hardcoded the ip and mac of D2. Isnt that sufficient?

Then, you have a major misunderstanding of basic networking.

Your configuration IS NOT sufficient. As @jeff stated:

Because D2 is not connected to R1 in any form or fashion. This is no different than if I gave you the MAC of my cell phone and you entered it into R1. You would never reach my cell phone via D1. As I noted before, router packets are conveyed via the MAC OF THE ROUTER, NOT THE MAC OF THE ENDPOINTS.

You have made 0 connections between D1 and D2 (and no connections between R1 and R1); so why do you believe you can send a datagram between them?

R1 never will even try to look for the MAC of D2 since D1 will look at its routing table, determine that D2's address is link-local to its interface. It will then send out an ARP request for D2, which will go unanswered as D2 is not link-local. R1 is completely uninvolved in the process.

Even if D1 has a static route for the address of D1 through R1, even if R1 has a static route for the address of D2 through R2, without a connection between R1 and R2, the packet will never reach R2.

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  • Please clearly explain what you mean by this (since you admit that, you are not referring to wired or WiFi connections between R1 and R2)?
  • Identify this "air" you reference?
  • Explain how it connects D1<>R1<>R2<>D2?
  • If you don't wish to connect R1 and R2, explain why both R1 and R2 are required in your setup?
  • Please explain your experiment in more detail.

@banerjee.152, how many kilometers apart can your move your 2 sets of devices - and still expect to send/receive the packets (since they are not connected anyway)?

This is some kind of a bad joke, right?

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the plot thickens :slight_smile:

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Perhaps it involves Class E address space :stuck_out_tongue_winking_eye:

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maybe it is this new feature called mobile ip :smiley:

If you have two AP's with the same MAC (BSSID) address where a client can be within radio range of both of them, there is a serious problem. Only one will have a particular client authenticated and associated on it. The other one will see packets (legitimately transmitted by the client, but intended for the other AP) incoming with its MAC address, but not be able to match them to a valid connection it its association table. This is called an "out of sequence" packet.

The AP will respond by sending a deauth to the client. The client will receive that deauth and assume that it came from the other AP, since it has the matching MAC as the AP it is associated with. This causes the client to tear down its connection with the first AP. The next packet that AP sends will be rejected as out of sequence by the client. This will cause the client to send a deauth packet to the first AP (well actually to both of them), and it will be fully disconnected from it.

So this cloned MAC AP has not only failed to usefully intercept any packets that were not intended for it, it has also broken the other intended connection.

Note that all of this happens within the wifi layer 1 operations. The packets never make it out of the wifi driver to be considered by the ARP table.

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