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30 votes

Network bridging - what's the point?

You are forgetting your history. Nowadays, almost everything is a bridge, and your collision domain is just a cable, which only has traffic from one source on any given pair (and thus, no collisions). ...
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21 votes

Network bridging - what's the point?

Modern network switches are essentially multi-port bridges. A network bridge (aka a transparent bridge) has the following characteristics: It operates at the Data Link layer (OSI model Layer 2) It ...
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19 votes
Accepted

Docker breaks libvirt bridge network

The problem, actually a feature: br_netfilter From the description, I believe the only logical explanation is that the bridge netfilter code is enabled: intended among other usages for stateful ...
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  • 8,702
17 votes
Accepted

What is the systemd-networkd equivalent of post-up? (dynamic bridge MAC configuration)

It turns out that due to the heavy modular concept of systemd and systemd-networkd the scripting question needs to be tackled from a different angle: instead of looking for scripting with the bridge ....
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  • 541
15 votes

Bridging wlan0 to eth0

Bridge wlan and 4addr: Bridging wlan0 is a pain. You normally cannot add it to a bridge interface (brctl returns "Operation not permitted"), and using VirtualBox "bridged" filter ...
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  • 359
15 votes
Accepted

How should I bridge two networks, given each network has its own subnet & DHCP server?

DHCP is based on using layer 2 broadcasts to allow clients to locate DHCP servers. A bridge would forward these layer 2 broadcasts between the networks. Plugging the switches from each respective ...
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11 votes
Accepted

Iptables: Matching packets for bridged interface

Reasons for observed behviour The reason that iptables doesn't get the physical bridge information when the packet arrives from a non-bridged interface is that the packet has never been near the ...
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11 votes

Possible to list members of a network bridge?

Alternatively, there's a more recent command provided by iproute2, used together with ip link to manage bridges: the bridge command. It can handle new bridge features not available through brctl (like ...
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  • 8,702
10 votes

Configuring 1:1 Nat using Firewalld for VM's

NAT is done at the firewall/router level. Depending on your firewall/router you can setup 1:1 NAT's the only thing to keep in mind is you can only setup one port to one IP. So if you have 2 web ...
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9 votes

Cannot ioctl TUNSETIFF tap0: Device or resource busy (errno=16)

This happens if you did not stop the service openvpn and immediately made changes to the configuration file - as a result, after restarting, you still have a lost process with the old interface. It is ...
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7 votes
Accepted

How can I connect my switch to my fibre connection?

You are mixing the roles of switches and routers, and this is the source of your confusion. A switch is a device which connects devices in the same network (this is greatly simplified, but let's roll ...
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  • 68.4k
6 votes
Accepted

Azure Site-to-Site VPN with a Linux based router to bridge the VPN ports to a RRAS server while keeping NAT for other traffic

So I've managed to figure this out after a lot of digging around, I am able to use the native Azure Site-to-Site VPN functionality with OpenSwan which runs on a linux box (Raspberry Pi/Arch Linux) ...
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  • 123
6 votes

How can I block all traffic to/from an bridged interface while allowing DHCP?

Yes, you need ebtables to apply netfilter rules on a bridge. The match rule is ip with parameters --ip-source-port and --ip-destination-port. You'd configure ebtables to allow the traffic you want, ...
6 votes
Accepted

Amazon EC2: OpenVPN server won't route bridged packets from client to VPC subnet

Your VPN needs to be routed, not bridged, and the subnet that your VPN clients are on has to be outside the bounds of the VPC supernet. Then, you add a static route for the VPN client subnet in the ...
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6 votes

Why must the IP be configured on the bridge device?

Thee was a very similar q on UL: https://unix.stackexchange.com/questions/86056/why-does-linux-require-moving-ip-from-eth-interface-to-bridge-interface The analiogy is that ETH resembles an uplink L1 ...
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  • 7,657
6 votes

network configuration (bridging) proxmox

Your network configuration is wrong. The host needs only it's own IP address, and you must configure the VM's network on its side, not on the host one. vmbr0 is the host's bridge to eth0, so eth0 ...
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  • 1,773
6 votes
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Linux: bridges, VLANs and RSTP

In Linux, VLANs and bridges are completely separate constructs, and Linux bridges are are not "VLAN aware". When you create a VLAN interface, Linux tags/untags packets on that interface before ...
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6 votes

Linux: bridges, VLANs and RSTP

Since Linux kernel 3.0 or so, it's no longer true that Linux bridges are "not VLAN aware". https://linux-blog.anracom.com/2017/10/30/fun-with-veth-devices-in-unnamed-linux-network-namespaces-i/ and ...
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6 votes

In virtual networking, how does a Virtual Switch differ from a linux kernel bridge?

First of all, many terms in IT are created by marketing departments, so they mean whatever the manufacturer wants it to mean. Functionally, bridges and switches are the same thing. They forward ...
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  • 2,149
5 votes
Accepted

Assign ipv6 address to KVM guests on bridge mode

So with the notice from Mark, I will answer my own question. Host setup: Assign the IPv6 sub block to your virtual bridge, in my example: Add <ip family='ipv6' address='2607:beef:be:beef:1::' ...
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  • 338
5 votes

Bridged Networking with bhyve and FreeBSD Guests does not work

You likely need to do: ifconfig tap0 up and/or add net.link.tap.up_on_open=1 to /etc/sysctl.conf to make it auto-up. Normally, the tap interface doesn't come up until you give it an IP. This ...
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  • 1,226
5 votes

Bridging wlan0 to eth0

4addr as described in other answers is certainly the best way when supported by the adapter/driver, but not all of them does. NAT might work for some things, but getting proper communication both ways ...
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5 votes

Bridging wlan0 to eth0

Depends on how mean the AP is to you: 1) It might only want to see packets coming from you, with your known link layer address (and hence not of bridged packets) 2) It might actually be even smarter, ...
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  • 321
5 votes

Iptables - Bridge and Forward chain

If you do not have the need to use iptables with the bridge on your system you can permanently disable it by using either of the following: Adding an iptables rule: iptables -I FORWARD -m physdev --...
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  • 241
5 votes
Accepted

How to match both sides of a virtual ethernet link?

As you suspect, the @if13 does refer to the number in the first column, which is the ifindex number (at least, "ifindex" is the name of the variable exposed by libnl, used to talk netlink to the ...
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  • 166
5 votes
Accepted

Why do I need restart a VM after restarted a bridge to get network working?

When you take the bridge down it disconnects all the attached IFs, when you bring it back up, only the IFs defined in ifcfg files (or whatever ubuntu uses instead) are added automatically. KVM guests ...
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  • 18.4k
5 votes

Why do we need a LAN physical interface bridged with OpenVPN TAP interface to get functional OpenVPN in bridge mode?

OpenVPN tap interface operates at the layer 2 of the ISO/OSI model and so it needs a layer 2 (read: bridge/switch) connection to the main, real interface. I strongly suggest you to reconfigure your ...
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  • 43.6k
5 votes

How to configure firewall on user defined Docker bridge?

Elaborating on Marek's Answer of setting the bridge name at creation time. docker network create --driver bridge -o \ "com.docker.network.bridge.name"="mynetwork_name" mynetwork or if using a ...
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5 votes

Ping does not work on TAP interfaces with bridge

I think you didn't grasp what's the role and usage of tun/tap interfaces, and that's the cause of your problems. Let me explain. Consider the tap0 interface as the end of a virtual wire with two ...
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  • 8,702
4 votes

ARP replies contain wrong MAC address

I know this is an old issue but I recently encountered the exact same situation with an embedded device. The device has both an ethernet and wifi interface and the requirements are that both ...
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