Based on Martin's hint I tried an experiment - I configured em0 statically instead of using dhcp. This fixes my problem.
So to summarize: in 6.0 running dhclient on a bridge-member interface breaks dhcp traffic passing through the bridge. This worked in 5.9. Also the FAQ bridge example uses DHCP on a member interface: http://www.openbsd.org/faq/faq6.html#Bridge My working configuration without dhclient: $ cat /etc/hostname.em0 inet 192.168.0.100 255.255.255.0 $ cat /etc/hostname.em1 up $ cat /etc/hostname.bridge0 add em0 add em1 up $ netstat -rn Routing tables Internet: Destination Gateway Flags Refs Use Mtu Prio Iface default 192.168.0.1 UGS 4 732 - 8 em0 224/4 127.0.0.1 URS 0 1278 32768 8 lo0 127/8 127.0.0.1 UGRS 0 0 32768 8 lo0 127.0.0.1 127.0.0.1 UHl 2 30 32768 1 lo0 192.168.0/24 192.168.0.100 UC 3 1449 - 4 em0 192.168.0.1 5a:ea:1d:96:c6:a8 UHLc 1 852 - 4 em0 192.168.0.7 14:99:e2:2b:f8:bc UHLc 0 572 - 4 em0 192.168.0.15 d8:a2:5e:95:8e:e8 UHLc 1 239 - 4 em0 192.168.0.100 00:07:e9:19:e0:02 UHLl 0 247 - 1 em0 192.168.0.255 192.168.0.100 UHb 0 34 - 1 em0 Internet6: Destination Gateway Flags Refs Use Mtu Prio Iface ::/96 ::1 UGRS 0 0 32768 8 lo0 ::/104 ::1 UGRS 0 0 32768 8 lo0 ::1 ::1 UHl 14 14 32768 1 lo0 ::127.0.0.0/104 ::1 UGRS 0 0 32768 8 lo0 ::224.0.0.0/100 ::1 UGRS 0 0 32768 8 lo0 ::255.0.0.0/104 ::1 UGRS 0 0 32768 8 lo0 ::ffff:0.0.0.0/96 ::1 UGRS 0 0 32768 8 lo0 2002::/24 ::1 UGRS 0 0 32768 8 lo0 2002:7f00::/24 ::1 UGRS 0 0 32768 8 lo0 2002:e000::/20 ::1 UGRS 0 0 32768 8 lo0 2002:ff00::/24 ::1 UGRS 0 0 32768 8 lo0 fe80::/10 ::1 UGRS 0 0 32768 8 lo0 fec0::/10 ::1 UGRS 0 0 32768 8 lo0 fe80::1%lo0 fe80::1%lo0 UHl 0 0 32768 1 lo0 ff01::/16 ::1 UGRS 0 0 32768 8 lo0 ff01::%lo0/32 ::1 Um 0 1 32768 4 lo0 ff02::/16 ::1 UGRS 0 0 32768 8 lo0 ff02::%lo0/32 ::1 Um 0 1 32768 4 lo0 # cat /etc/pf.conf # $OpenBSD: pf.conf,v 1.54 2014/08/23 05:49:42 deraadt Exp $ # # See pf.conf(5) and /etc/examples/pf.conf - hide quoted text - ext_if = "em0" int_if = "em1" set skip on lo set loginterface $ext_if set block-policy drop set limit states 50000 pass on $ext_if all pass on $int_if all $ dmesg OpenBSD 6.0 (GENERIC.MP) #1: Sat Sep 3 06:59:42 CDT 2016 root@server.domain:/usr/src/sys/arch/amd64/compile/GENERIC.MP RTC BIOS diagnostic error 80<clock_battery> real mem = 1045643264 (997MB) avail mem = 1009541120 (962MB) mpath0 at root scsibus0 at mpath0: 256 targets mainbus0 at root bios0 at mainbus0: SMBIOS rev. 2.4 @ 0xe35a0 (23 entries) bios0: vendor Intel Corp. version "LF94510J.86A.0278.2010.0414.2000" date 04/14/2010 bios0: Intel Corporation D945GCLF2 acpi0 at bios0: rev 2 acpi0: sleep states S0 S1 S3 S4 S5 acpi0: tables DSDT FACP APIC WDDT MCFG ASF! acpi0: wakeup devices SLPB(S4) P32_(S4) UAR1(S4) UAR2(S4) PEX0(S4) PEX1(S4) PEX2(S4) PEX3(S4) PEX4(S4) PEX5(S4) UHC1(S3) UHC2(S3) UHC3(S3) UHC4(S3) EHCI(S3) AC9M(S4) [...] acpitimer0 at acpi0: 3579545 Hz, 24 bits acpimadt0 at acpi0 addr 0xfee00000: PC-AT compat cpu0 at mainbus0: apid 0 (boot processor) cpu0: Intel(R) Atom(TM) CPU 330 @ 1.60GHz, 1596.27 MHz cpu0: FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,CFLUSH,DS,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT,TM,PBE,SSE3,DTES64,MWAIT,DS-CPL,TM2,SSSE3,CX16,xTPR,PDCM,MOVBE,NXE,LONG,LAHF,PERF,SENSOR cpu0: 512KB 64b/line 16-way L2 cache cpu0: smt 0, core 0, package 0 mtrr: Pentium Pro MTRR support, 7 var ranges, 88 fixed ranges cpu0: apic clock running at 133MHz cpu0: mwait min=64, max=64, C-substates=0.1, IBE cpu1 at mainbus0: apid 1 (application processor) cpu1: Intel(R) Atom(TM) CPU 330 @ 1.60GHz, 1596.01 MHz cpu1: FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,CFLUSH,DS,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT,TM,PBE,SSE3,DTES64,MWAIT,DS-CPL,TM2,SSSE3,CX16,xTPR,PDCM,MOVBE,NXE,LONG,LAHF,PERF,SENSOR cpu1: 512KB 64b/line 16-way L2 cache cpu1: smt 0, core 1, package 0 ioapic0 at mainbus0: apid 2 pa 0xfec00000, version 20, 24 pins acpimcfg0 at acpi0 addr 0xf0000000, bus 0-127 acpiprt0 at acpi0: bus 0 (PCI0) acpiprt1 at acpi0: bus 4 (P32_) acpiprt2 at acpi0: bus 1 (PEX0) acpiprt3 at acpi0: bus -1 (PEX1) acpiprt4 at acpi0: bus 2 (PEX2) acpiprt5 at acpi0: bus 3 (PEX3) acpiprt6 at acpi0: bus -1 (PEX4) acpiprt7 at acpi0: bus -1 (PEX5) acpicpu0 at acpi0: C1(@1 halt!) acpicpu1 at acpi0: C1(@1 halt!) acpibtn0 at acpi0: SLPB "PNP0003" at acpi0 not configured pci0 at mainbus0 bus 0 pchb0 at pci0 dev 0 function 0 "Intel 82945G Host" rev 0x02 inteldrm0 at pci0 dev 2 function 0 "Intel 82945G Video" rev 0x02 drm0 at inteldrm0 intagp0 at inteldrm0 agp0 at intagp0: aperture at 0x40000000, size 0x10000000 inteldrm0: apic 2 int 16 inteldrm0: 1920x1080 wsdisplay0 at inteldrm0 mux 1: console (std, vt100 emulation) wsdisplay0: screen 1-5 added (std, vt100 emulation) ppb0 at pci0 dev 28 function 0 "Intel 82801GB PCIE" rev 0x01: msi pci1 at ppb0 bus 1 1:0:0: mem address conflict 0xfffe0000/0x20000 re0 at pci1 dev 0 function 0 "Realtek 8168" rev 0x02: RTL8168C/8111C (0x3c00), msi, address 00:1c:c0:f0:cf:9c rgephy0 at re0 phy 7: RTL8169S/8110S/8211 PHY, rev. 2 ppb1 at pci0 dev 28 function 2 "Intel 82801GB PCIE" rev 0x01: msi pci2 at ppb1 bus 2 ppb2 at pci0 dev 28 function 3 "Intel 82801GB PCIE" rev 0x01: msi pci3 at ppb2 bus 3 uhci0 at pci0 dev 29 function 0 "Intel 82801GB USB" rev 0x01: apic 2 int 23 uhci1 at pci0 dev 29 function 1 "Intel 82801GB USB" rev 0x01: apic 2 int 19 uhci2 at pci0 dev 29 function 2 "Intel 82801GB USB" rev 0x01: apic 2 int 18 uhci3 at pci0 dev 29 function 3 "Intel 82801GB USB" rev 0x01: apic 2 int 16 ehci0 at pci0 dev 29 function 7 "Intel 82801GB USB" rev 0x01: apic 2 int 23 usb0 at ehci0: USB revision 2.0 uhub0 at usb0 "Intel EHCI root hub" rev 2.00/1.00 addr 1 ppb3 at pci0 dev 30 function 0 "Intel 82801BA Hub-to-PCI" rev 0xe1 pci4 at ppb3 bus 4 em0 at pci4 dev 0 function 0 "Intel 82546EB" rev 0x01: apic 2 int 21, address 00:07:e9:19:e0:02 em1 at pci4 dev 0 function 1 "Intel 82546EB" rev 0x01: apic 2 int 22, address 00:07:e9:19:e0:03 pcib0 at pci0 dev 31 function 0 "Intel 82801GB LPC" rev 0x01 pciide0 at pci0 dev 31 function 1 "Intel 82801GB IDE" rev 0x01: DMA, channel 0 configured to compatibility, channel 1 configured to compatibility pciide0: channel 0 disabled (no drives) pciide0: channel 1 ignored (disabled) pciide1 at pci0 dev 31 function 2 "Intel 82801GB SATA" rev 0x01: DMA, channel 0 configured to native-PCI, channel 1 configured to native-PCI pciide1: using apic 2 int 19 for native-PCI interrupt wd0 at pciide1 channel 0 drive 0: <SAMSUNG SP2504C> wd0: 16-sector PIO, LBA48, 238475MB, 488397168 sectors wd0(pciide1:0:0): using PIO mode 4, Ultra-DMA mode 6 ichiic0 at pci0 dev 31 function 3 "Intel 82801GB SMBus" rev 0x01: apic 2 int 19 iic0 at ichiic0 admtm0 at iic0 addr 0x2d: 47m192 spdmem0 at iic0 addr 0x50: 1GB DDR2 SDRAM non-parity PC2-4200CL5 usb1 at uhci0: USB revision 1.0 uhub1 at usb1 "Intel UHCI root hub" rev 1.00/1.00 addr 1 usb2 at uhci1: USB revision 1.0 uhub2 at usb2 "Intel UHCI root hub" rev 1.00/1.00 addr 1 usb3 at uhci2: USB revision 1.0 uhub3 at usb3 "Intel UHCI root hub" rev 1.00/1.00 addr 1 usb4 at uhci3: USB revision 1.0 uhub4 at usb4 "Intel UHCI root hub" rev 1.00/1.00 addr 1 isa0 at pcib0 isadma0 at isa0 pckbc0 at isa0 port 0x60/5 irq 1 irq 12 pckbd0 at pckbc0 (kbd slot) wskbd0 at pckbd0: console keyboard, using wsdisplay0 pcppi0 at isa0 port 0x61 spkr0 at pcppi0 vscsi0 at root scsibus1 at vscsi0: 256 targets softraid0 at root scsibus2 at softraid0: 256 targets root on wd0a (c24ccd52000f4972.a) swap on wd0b dump on wd0b
