👀 Views: 37 💬 Answers: 1 📅 Created: 2025-06-12

linux iptables ubuntu bash

I've searched everywhere and can't find a clear answer. Does anyone know how to I'm trying to configure NAT on my Ubuntu 22.04 server using `iptables`, but I'm running into an scenario where I get a 'Chain already exists' behavior when I attempt to create a new chain... My goal is to set up a simple NAT to allow my internal network to access the internet. I've followed several tutorials and here’s what I’ve done so far: I started by flushing the existing rules with: ```bash sudo iptables -F ``` Next, I attempted to create a new chain for my NAT rules: ```bash sudo iptables -N MYCHAIN ``` However, I received the following behavior: ``` iptables: Chain already exists ``` I verified that there are no existing chains with: ```bash sudo iptables -L ``` The output shows the default chains, but I need to find `MYCHAIN`. I've also checked the services running on my server and confirmed that there are no conflicting services or configurations related to `iptables`. After this, I tried to directly manipulate the NAT table: ```bash sudo iptables -t nat -N MYCHAIN ``` But I received the same behavior again. To circumvent this, I attempted to delete the chain first, thinking that might help: ```bash sudo iptables -t nat -D MYCHAIN ``` This also resulted in an behavior: ``` iptables: No chain/target/match by that name ``` I’ve ensured that `iptables` is properly installed and I’m running as a user with sufficient privileges. I’ve also looked into using `nftables` as an alternative, but I would prefer to resolve this scenario with `iptables` for now. Any guidance on how I can solve this 'Chain already exists' behavior would be greatly appreciated! For context: I'm using Bash on Ubuntu. What's the best practice here? For reference, this is a production CLI tool. I'm working on a microservice that needs to handle this.