I just have upgraded two servers from Debian 10 (Buster) to Debian 11 (Bullseye). Afterwards, I could not reach either of them via network any more. After some investigation, the following problem turned out:

Both machines have a bridge device configured. Obviously, the algorithm which Debian uses to assign MAC addresses to bridge devices has changed from version 10 to 11. After the upgrade, the bridge device on the first server had the same MAC address as the bridge device on the second server, which for sure has not been the case before.

One of the answers there claims that a bridge is a purely internal device and that therefore a bridge's MAC address does not matter. However, this is obviously wrong. At least in my case, packets from both machines were outgoing with the HW source address being the bridge's MAC address, and the network ports on both machines were processing incoming packets only if they were destined for the bridge's MAC address.

Since that MAC address was the same on both machines, the network became unusable, which is completely logical and understandable.

How can I make Debian generate different MAC addresses for bridge devices which are on different machines (or even on the same machine, but that's currently not my issue)?

I have just upgraded two servers from Debian 10 (Buster) to Debian 11 (Bullseye). Afterwards, I could not reach either of them via the network any more. After some investigation, the following problem turned out:

Both machines have a bridge device configured. Obviously, the algorithm which Debian uses to assign MAC addresses to bridge devices has changed from version 10 to 11. After the upgrade, the bridge device on the first server had the same MAC address as the bridge device on the second server, which for sure has not been the case before.

One of the answers there claims that a bridge is a purely internal device and that therefore a bridge's MAC address does not matter. However, this is obviously wrong. At least in my case, packets from both machines were outgoing with the hardware source address being the bridge's MAC address, and the network ports on both machines were processing incoming packets only if they were destined for the bridge's MAC address.

Since that MAC address was the same on both machines, the network became unusable, which is completely logical and understandable.

How can I make Debian generate different MAC addresses for bridge devices which are on different machines (or even on the same machine, but that's currently not my issue)?

I just have upgraded two servers from Debian 10 (Buster) to Debian 11 (Bullseye). Afterwards, I could not reach either of them via network any more. After some investigation, the following problem turned out:

Both machines have a bridge device configured. Obviously, the algorithm which Debian uses to assign MAC addresses to bridge devices has changed from version 10 to 11. On both machines, the bridge devices had the same MAC address after the upgrade., which for sure has not been the case before.

One of the answers there claims that a bridge is a purely internal device and that therefore a bridge's MAC address does not matter. However, this is obviously wrong. At least in my case, packets from both machines were outgoing with the HW source address being the bridge's MAC address, and the network ports on both machines were processing incoming packets only if they were destined for the bridge's MAC address.

Since that MAC address was the same on both machines, the network became unusable, which is completely logical and understandable.

How can I make Debian generate different MAC addresses for bridge devices which are on different machines (or even on the same machine, but that's currently not my issue)?

I just have upgraded two servers from Debian 10 (Buster) to Debian 11 (Bullseye). Afterwards, I could not reach either of them via network any more. After some investigation, the following problem turned out:

Both machines have a bridge device configured. Obviously, the algorithm which Debian uses to assign MAC addresses to bridge devices has changed from version 10 to 11. After the upgrade, the bridge device on the first server had the same MAC address as the bridge device on the second server, which for sure has not been the case before.

One of the answers there claims that a bridge is a purely internal device and that therefore a bridge's MAC address does not matter. However, this is obviously wrong. At least in my case, packets from both machines were outgoing with the HW source address being the bridge's MAC address, and the network ports on both machines were processing incoming packets only if they were destined for the bridge's MAC address.

Since that MAC address was the same on both machines, the network became unusable, which is completely logical and understandable.

How can I make Debian generate different MAC addresses for bridge devices which are on different machines (or even on the same machine, but that's currently not my issue)?