GRE dont-fragment - inherit from where?

RouterOS General
1

Ok, I understand the concept of “don’t fragment”. But on a GRE interface we have two options:

  1. “No”. Meaning “ok, fragment if needed”
  2. “inherit”. Meaning “inherit the value from…” From where? That’s what I want to know.

Where does the value come from, if I choose “inherit”?

2

I’m pretty sure it means the parent device’ setting if there is one, otherwise yes.

3

Which parent device? The GRE tunnel just exists, it isn’t attached to some interface. Would it be the interface through the connection is made?

4

I always assumed it inherits it from the packet being encapsulated. Not sure this assumption is correct, though.

5

afaik, inherent indeed means “use DF flag” of original packet. Note a GRE interface is unaware of its parent interface, all you specify is an IP local/remote addresses for the tunnel

6

Well, it makes sense, to use the flag from the encapsulated packet.

7

Sorry, that was a bad wording… I meant the interface by which the connection was made through…

8

But I think andriys and others are right, it means to copy don’t fragment from the encapsulated packet to the outer GRE packet.
(same for DSCP)