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Could someone explain these OpenWRT LuCI firewall settings to me? I am having trouble interpereting what they are saying exactly.
(sh.itjust.works)
cross-posted to: https://sh.itjust.works/post/14114626
If the rule is about forwarding traffic from the lan interface to the wan interface, then why is there also a forward rule? How would inputs, and outputs make any sense if the rule is talking about forwarding? What does it mean for wan to forward to REJECT? I interperet that as saying that wan doesn't go anywhere, but that wouldn't make sense given that the router can send, and receive over the internet.
For example I would interperet the first rule as follows:
lan => wan: the conditions for which connections from thelaninterface are forwarded to to thewaninterface.Input: accept: thelaninterface accepts all connections originating from the network (I wouldn't understand the point of setting this to bereject).Output: accept: all connections exiting thewaninterface are accepted (again, I'm not sure what the point of this would be).Forward: accept: forwarding of packets fromlantowanis allowed.- Masquerade: I honestly don't know what the effect of enabling this would be. What would it mean to masquerade the
laninterface?
I tried finding documentation, and I did come across this, and this, but, from what I could understand, they didn't really answer any of my questions.
Input means the packet stops at the router, like when you access its web ui. I don't think you want to give the internet access to your router settings :)
Ah okay, so if
Output: acceptis still enabled, then, even thoughInput: rejectis set, the packet can still use the router as a hop in it's journey to a device on the router's network? It just can't stop at the router? I guess that makes sense because the device on the routers network is addressed by a port which is a layer above the IP address, so it wouldn't even have a notion of addressing the router unless it just specifies the raw IP.[EDIT (2024-02-08T00:21Z): Redacted this paragraph after re-reading this comment.]~~Another thing that is confusing me is the setting for
Forward. I would assume that if a packet is destined for a device on the router's network, then that packet is being forwarded fromwantolan, and ifMasqueradingis enabled, then the destination IP will be modified by the router. But, in the example image we have thatForward: rejectis set. How does the packet get forwarded between interfaces if forwarding is disabled?~~[EDIT (2024-02-08T00:21Z): Added the following quote, and response.]
How does the router differentiate between the two? If I remember correctly, nftbales uses conntrack to track this sort of stuff. I would guess that the router does the same?
[EDIT (2024-02-08T00:26Z): Added the following update.]
When I was looking through the settings for the second row, I came across the following setting:
I believe that this setting is accomplishing the behaviour that you described (not allowing connections from
wan, but still allowing responses). Correct?