无法桥接两个以太网接口，ping无响应且tcpdump无输出求助

Hey Abdul, let's break down what might be missing here. Since you're having trouble getting traffic to pass between your two Ethernet interfaces and aren't seeing any response to your ping or output in tcpdump, here are the key checks and fixes to walk through:

First, make sure your bridge is properly defined—this is the most common oversight. A valid bridge setup should tie both physical interfaces to a bridge interface (usually br0), and the physical interfaces shouldn't have their own IP addresses. Here's what a correct config might look like:

auto br0
iface br0 inet static
address 192.168.0.xxx/24 # Use an IP in your network range
gateway 192.168.0.1
bridge_ports enp0s3 enp0s8
bridge_stp off # Disable spanning tree if it's a simple setup
bridge_fd 0
bridge_maxwait 0

If your current config doesn't include the br0 bridge, or if enp0s3/enp0s8 have their own static IPs, that's a critical issue. The bridge should handle the IP for the combined interface, while the physical ports stay as "dumb" members of the bridge.

Even with a bridge, Linux won't route traffic between interfaces unless IP forwarding is enabled. Check its current state with:
sysctl net.ipv4.ip_forward
If the output is net.ipv4.ip_forward = 0, enable it temporarily with:
sudo sysctl -w net.ipv4.ip_forward=1
To make this permanent (so it survives reboots), add or update this line in /etc/sysctl.conf:
net.ipv4.ip_forward=1

On Debian/Ubuntu-based systems, you need the bridge-utils package to create and manage bridges. Install it with:
sudo apt update && sudo apt install bridge-utils
After installation, restart your networking service to apply changes:
sudo systemctl restart networking

Run these commands to verify both interfaces are active and attached to the bridge:

• ip link show enp0s3 and ip link show enp0s8: Look for UP,LOWER_UP in the output to confirm the interface is enabled.
• brctl show: This should list br0 with both enp0s3 and enp0s8 listed under the ports column.

If an interface is down, bring it up with:
sudo ip link set enp0sX up (replace X with 3 or 8)

Your firewall (like ufw or iptables) might be dropping the ping or bridge traffic. Test by temporarily disabling it:

• For ufw: sudo ufw disable
• For iptables: sudo iptables -F && sudo iptables -P INPUT ACCEPT && sudo iptables -P OUTPUT ACCEPT && sudo iptables -P FORWARD ACCEPT

If ping works after disabling, you'll need to add rules to allow bridge traffic. For ufw, allow all traffic on the bridge interface:
sudo ufw allow in on br0 && sudo ufw allow out on br0

Don't skip the basics! Make sure:

• enp0s8 is actually connected to the network where 192.168.0.1 is located (check cables if wired, or virtual network adapter settings if this is a VM).
• The device at 192.168.0.1 is online and accepting pings.

After working through these steps, retry your ping -I enp0s8 192.168.0.1 command and check tcpdump on enp0s3—you should start seeing traffic pass through.

内容的提问来源于stack exchange，提问作者Abdul Rahman