In network-based models such as OSI or TCP / IP, is it possible for data in each layer to be delivered incompletely to the lower layer?
For example, might layer 3 send data to the second layer without writing an IP?
If yes, please explain about the items that do not include IP address or MAC address?

  • Why is it incomplete? The second layer doesn't care whether its payload contains an IP address or not.
    – user1686
    May 10 at 6:10
  • @user1686 I know the second layer does not matter to the IP address. I mean, if the third layer does not specify the IP, it sends the data to the next layer?
    – Truth
    May 10 at 6:16
  • I'm not sure I'm getting the point of the question. L3 can do anything it needs to do. Are you asking about specific protocols acting as L3, or are you asking about the general concept of "layer 3" in general? I mean, IP will always include an IP header, but there exist layer-3 protocols that aren't IP to begin with, and there's really no requirement that the L2 payload even be a L3 protocol; it could directly be an application protocol.
    – user1686
    May 10 at 6:21
  • 1
    If you use IP as the third layer, each packet has a source and destination address in the IP header. I don't see how these addresses can be removed from the header. You can put put random numbers in them, or zeros, or 0xffffffff, but something is in those fields. Whether it makes sense and the packet goes somewhere is a different question. However, at least in the OSI model you could use something else than IP as the third layer. In this case, layer 3 headers have no IP addresses. May 10 at 7:17

Theoretically yes, practically the question doesn't really make much sense.

In layman's terms, when a layer 3 packet is encapsulated into a layer 2 frame, the whole packet is "used". There is no data taken out or added from "within" the packet. So if it the data gets passed on to the next layer and it doesn't have an IP address it didn't have an IP address to begin with. But the packet would get encapsulated anyway.

A packet without an IP is not a "valid" packet so it probably would have been rejected at some point prior to the encapsulation form layer 3 to layer 2 but that all depends on the actual implementation of the software involved in the communication process.

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