> Generally (but not always) an IP filter would be applied irrespective of protocol
I've never seen this (all protocols by default) in any environment I've personally worked with, but perhaps I've had a unique experience.
I've never seen this (all protocols by default) in any environment I've personally worked with, but perhaps I've had a unique experience.
I did not assume. The comment to which I was responding suggested it was the destination IP that was the problem. Generally (but not always) an IP filter would be applied irrespective of protocol. I also pointed out that the initial SYN and reply SYN/ACK are getting through the hypothesized bogon filter and those are part of TCP. I don't think the bogon filter is a hypothesis that fits the evidence.
ETA: but adding connection state tracking + a filter does make sense https://news.ycombinator.com/item?id=39822214