[thefronny]

Originally Posted by jggimi

Let's start with a level-set on routing. Please excuse me if this is review.

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In IP, a routing table contains two entries: a destination subnet, and the "next hop" to get there. For example, let us pretend that communication is to flow between system A and system E:

[A] - [B] - [C] - [D] - [E]

The routing table in system A needs to have an entry for a subnet which includes the address of system E, which points to the "next hop" system B. That's all it needs. B then needs to know about C, and so on. For returning traffic, system E needs to know to use its "next hop" D to reach A.

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Your router's address changed, and your OpenBSD system had been statically configured. To use my example, if your OpenBSD firewall is "B" and your "outside" local router is "C", the address of "C" changed on that "B to C" local network.

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A default route is a "next hop" entry for the subnet 0.0.0.0/0. This is "all IP addresses." A system on a local network with a single router will have a default route entry that points to the "next hop" local router. That is the only way to reach "all IP addresses" that aren't on the local subnet.

Thank you for this. Much more clear for me now.