How do you choose between NAT and bridge mode for your VM network? (2024)

Choosing between NAT and bridge mode for VM networking depends on your needs. NAT mode offers security and ease of setup, isolating the VM from external networks; it's ideal when external network access isn't crucial. The VM shares the host's IP but is in a separate network, suitable for secure environments. Bridge mode, conversely, integrates the VM directly into the host's network, assigning it a unique IP. This is beneficial for seamless network integration, allowing the VM to communicate directly with other network devices. Opt for NAT for security and isolation, and bridge mode for direct network engagement.

if your VMs need complete isolation from the host operating system and other VMs on the same physical network segment and direct access without using NAT or if network performance is critical for your workload then bridge mode is the best option for your VM network configuration; otherwise NAT mode is the best choice for conserving IP addresses and when VMs do not need direct access or when network performance is less critical for your workload

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NAT is the default option in most the virtualization software and library (API) because it's simple and secure. In the real world, at home for instance, your ISP router is working with NAT for providing internet access. All your computers, connected objects can access internet with only one IP on the router so that the idea behind NAT. So for most of the people NAT it's enough. But If you have more needs than a simple internet access you should switch to the bridge mode.

Network Address Translation (NAT) mode is a networking configuration used for VMs where the host machine acts as an intermediary between the VMs and the external network.1. Each VM is assigned a private IP address within a virtual network managed by the host machine. When a VM needs to communicate with an external network (e.g., the internet), the host machine translates the VM’s private IP address to its own public IP address. Outbound traffic from the VM appears to originate from the host machine’s IP address.2. Inbound Traffic: By default, external devices cannot directly initiate communication with the VMs. To allow inbound traffic, specific ports on the host machine can be forwarded to the corresponding ports on the VMs.

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We called "Bridge" but it's more a switch, so it's work like a switch in virtual like in the real world. It's the most versatile option whe, you try to create a virtual network. You can make everything you want like it was physical. So yes it's a little bit more complicated but at the end it can answer to all yours needs. Unlike NAT, IP, DNS etc, ... are provided outside the box and of course you need more IPs (but that not a bigdeal in private network). And between us, you allready have theses services (DHCP, DNS, NTP, ...). So if you want bonderies adopt "bridge" for your virtual boxes.

Bridge Mode is a networking configuration for virtual machines (VMs) where the VMs are connected directly to the same network as the host machine, effectively allowing them to behave like physical devices on that network.1. In Bridge Mode, the virtual network adapter of each VM is connected directly to the physical network adapter of the host machine. This setup allows VMs to receive IP addresses from the same DHCP server or use static IP addresses on the physical network.2. VMs appear as separate devices on the network with their own unique IP addresses, just like any other physical device connected to the network.They can communicate with other devices on the network without additional translation or routing.

Quite simple, if you want to comunicate to your VMs from other hosts or publish services like a simple Web (HTTP/S) you should choose the bridge mode. Why.. Imaging this simple case, you have 2 VMs on the same host both of them have a web server published on port 80. In NAT use cases at the end you have only one IP (most of the time the one of your host) you can't publish the 2 Web sites because you have only one port 80 on the host. Of course it's possible to publish on website on port 80 and the other on 8080 it's works but you see the limit of NAT use case. On the other hand, on the bridge mode, all the VMs have their own IP so it's possible to publish the two websites even more it's also possible to publish a third one on the host !!!

Some ways to get started: Overcome delaying starting a large, complicated task by executing on one small well-defined subtask to get yourself started.

Choosing between NAT and Bridge Mode for your VM network depends on your specific use case and network requirements such as Network Accessibility Requirements, Security Considerations, IP Address Management, Performance Management, Network Services and Integration and configuration complexity.

As I said NAT it's usually the default option so you don't need to do anything. Your host is providing everything (DNS, DHCP, ...). You just install the VM and you have access to internet, most of the time your VM is in DHCP mode so everything is automatic. Don't forget you go outside with the host IP. In brigde mode, usualy you should create one, depends of you operating system or distrib but in linux you can use network manager (nmcli) or the GUI (nmtui). Delete your connection (beware if your are remote), create the bridge with nmtui for instance and had the connection of your host to the bridge, at this stage you shoud have remote access. And now attach all your VMs to bridge. Have a look to your DHCP to see all the VM IPs.

Ping will be your best friend to debug NAT and Bridge.Don't forget your firewall rules !!!In linux you can also use brctl for managing advanced options of your bridge like STP, Hairpin, or ARP aging.

1. Network Service TestingDHCP: Verify that VMs can obtain IP addresses from a DHCP server if you’re using DHCP. Check the assigned IP address and ensure it’s in the correct range.DNS: Test DNS resolution by using commands like nslookup or dig to resolve domain names to IP addresses. Ensure that DNS queries return the correct results.2. Firewall and Security TestingAccess Control: Test access control rules and firewalls to ensure that they are correctly configured and that unauthorized access is blocked.3. Network Configuration TestingNetwork Interface: Verify that the network interfaces are correctly configured on each VM. Check IP addresses, subnet masks, and gateways.

In my lab at home I have all my KVM virtual machines in bridged mode and thus can take advantage of the various trunked vlans I have into the hypervisor host. Further though using bridged mode gives you a more authentic experience when you are testing requirements that have a network component to them. Further if you need outside access to the hosts I find its easier to deal with this in bridged mode vs NAT where you have to setup outside port mappings to inside for simple things like ssh or web services. All around NAT is useful for a quick dirty test of any outbound traffic but bridged will give you a better realistic experience.

If you are using Ethernet connection, in either mode, and you face connection problems, try to take off the wifi from your computer.