Source: libvirt Severity: normal Enabling of MAC addressed based filtering on bridge ports i.e setting in /etc/libvirt/qemu.conf mac_filter = 1 breaks dhcp clients in guest vm's. That happens because libvirt adds a rule to ebtables filter table only for outgoing packets:
# ebtables -t filter -L --Lc Bridge table: filter Bridge chain: INPUT, entries: 0, policy: ACCEPT Bridge chain: FORWARD, entries: 1, policy: ACCEPT -j libvirt_qemu_FORWARD, pcnt = 2951 -- bcnt = 334700 Bridge chain: OUTPUT, entries: 0, policy: ACCEPT Bridge chain: libvirt_qemu_FORWARD, entries: 1, policy: DROP -s 52:54:0:17:11:11 -i vnet0 -j ACCEPT , pcnt = 711 -- bcnt = 81576 So dhcp requests get to dhcp server but replies are filtered out, because we need another rule to let them to get in the guest vm: # ebtables -t filter -A libvirt_qemu_FORWARD -d 52:54:0:17:11:11 -o vnet0 -j ACCEPT -- System Information: Debian Release: buster/sid APT prefers stable-updates APT policy: (500, 'stable-updates'), (500, 'proposed-updates'), (500, 'testing'), (500, 'stable') Architecture: amd64 (x86_64) Kernel: Linux 4.14.0-3-amd64 (SMP w/64 CPU cores) Locale: LANG=ru_RU.UTF-8, LC_CTYPE=ru_RU.UTF-8 (charmap=UTF-8), LANGUAGE=ru_RU.UTF-8 (charmap=UTF-8) Shell: /bin/sh linked to /bin/dash Init: systemd (via /run/systemd/system)
