https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=296129
Bug ID: 296129
Summary: ether_gen_addr() change breaks existing bridge MAC
addresses on upgrade
Product: Documentation
Version: Latest
Hardware: amd64
OS: Any
Status: New
Severity: Affects Some People
Priority: ---
Component: Website
Assignee: [email protected]
Reporter: [email protected]
After upgrading from FreeBSD 14.4-RELEASE to 15.1-RELEASE, I observed that a
bridge interface on my host received a different auto-generated MAC address
despite identical inputs (hostuuid, interface name). This silently broke the
DHCP lease for that interface. Other bridge or virtual interfaces may be
similarly affected, since the underlying MAC generation algorithm changed.
Presumably caused by commit 604d34c23f772ae0005a552b0b7189f3dc97d519 (PR
256850), which changed how ether_gen_addr() constructs MACs from the SHA1
digest. Same inputs now
produce a different address. The commit is tagged "Relnotes: yes" but neither
the release notes nor the upgrade guide warn that existing MACs will change or
explain how to preserve them.
Steps to reproduce:
1. On FreeBSD 14.x, note the MAC of a bridge: `ifconfig bridge10 | grep ether`
2. Upgrade to 15.x.
3. The bridge MAC is now different.
This behavioral change is not mentioned in the errata for 15.0-RELEASE or
15.1-RELEASE. At a minimum it should be added as an errata entry for both
releases so administrators are aware before upgrading.
Affected versions: 15.0-RELEASE, 15.1-RELEASE (14.x not affected).
Workaround: pin the MAC in rc.conf (`ifconfig_bridge0="... ether
xx:xx:xx:xx:xx:xx ..."`).
Related: commit 604d34c23f772ae0005a552b0b7189f3dc97d519, PR 256850.
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