Should use the rightmost ip in x-forwarded-for, if used at all

[jarlandre]

https://adam-p.ca/blog/2022/03/x-forwarded-for/

For something as important as rate limiting, the rightmost ip in the header, separated by comma, should be used. Not the leftmost, even if that is "closest" to the client. Because it can be spoofed.

Im going to fork this repo and make the get getIPFromXFFHeader function return the last ip in the list. So that i can at least use this library

[jarlandre]

Just tell if its interesting that i make a PR into this repo from this MaindeckAS@a8425b3

[novln]

Hello,

As described here (https://github.com/ulule/limiter#limiter-behind-a-reverse-proxy) you should use what is best for your network topology. That's why it's disabled by default.

But word of caution, if you use the rightmost IP in the header you could rate limit your load balancer or CDN.

Just tell if its interesting that i make a PR into this repo [...]

No thank you, I plan to make a customizable system for the next major version.
I just need to find the motivation for this, I haven't been active recently.

[novln]

But thank you for mentioning your fork, I may use it when (or if) I'll implement a rightmost ip parser.

[jarlandre]

But word of caution, if you use the rightmost IP in the header you could rate limit your load balancer or CDN.

No, because aws alb appends client ip to XFF header. I dont know from where you have this idea, but its not valid in aws :) but no stress

[jarlandre]

btw the most funny part is i might not need to use this fix at all. Because i made a middleware that fixes XFF header to rightmost. So i can use all kinds of libraries like this without caring too much

[novln]

No, because aws alb appends client ip to XFF header. I dont know from where you have this idea, but its not valid in aws :)

As said before, that depend of your network topology: not everyone use AWS.
You could have an nginx with a public ip and then other nginx inside a VLAN, private network or an hypervisor that routes that to the correct VM / containers.

[jarlandre]

Yep, you are right :) Ill close this now, but feel free to use as inspiration, or not. I am currently using another solution for this problem.