IPFW redirect to another port?
karl at denninger.net
Tue Jun 18 17:56:12 UTC 2019
On 6/18/2019 11:50 AM, John Levine wrote:
> I would like to use ipfw to redirect incoming port 53 requests from a
> few IP addresses to a different port, so I can use a custom DNS server
> to answer them. I can figure out how to redirect their traffic to,
> say, port 5553, but the responses come from 5553 which of course
> doesn't work.
> Any suggestions about how to adjust the port numbers going both ways? It's
> fine if they screw up other traffic to those IPs. TIA.
The easiest way to do this is likely with an in-kernel NAT entry with a
"redirect_port" stanza; that will "twist" packets going in both
directions. The most-common use for this is to take something on the
external interface (e.g. 220.127.116.11:8080) and direct it at an internal host
on port 80 (e.g. 10.1.1.1:80); the "redirect_port" stanza allows for
both TCP and UDP redirection with both sides being translated.
-- Karl Denninger
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