Synopsis: dhcpd sends DHCPACK even if it is not named in DHCPREQUEST
Category: system
Environment:
System : OpenBSD 5.2
Details : OpenBSD 5.2 (GENERIC) #278: Wed Aug 1 10:04:16 MDT 2012
dera...@i386.openbsd.org:/usr/src/sys/arch/i386/compile/GENERIC
Architecture: OpenBSD.i386
Machine : i386
Description:
During the allocation of a network address, dhcpd might send DHCPACK
even if this server was not selected by the DHCP client.
When multiple DHCP servers offer the same lease to a client after
DHCPDISCOVER, each of these DHCP servers sends DHCPACK after receiving
the DHCPREQUEST broadcast from the client. Even though only one of them
was named in the DHCPREQUEST message.
According to http://tools.ietf.org/html/rfc2131#section-3.1
Quote:
3. [snip]
The client broadcasts a DHCPREQUEST message that MUST include
the 'server identifier' option to indicate which server it has
selected
[snip]
4. The servers receive the DHCPREQUEST broadcast from the client.
Those servers not selected by the DHCPREQUEST message use the
message as notification that the client has declined that server's
offer. The server selected in the DHCPREQUEST message commits the
binding for the client to persistent storage and responds with a
DHCPACK message containing the configuration parameters for the
requesting client.
End of quote.
ACK from all servers doesn't seem to happen, when the servers offer
different IP addresses, but I have not tested this scenario much.
It should be noticed, that section 3.2 of RFC2131 describes a scenario
where DHCPREQUEST doesn't have to include the 'server identifier'
option. The current implemention and behaviour of dhcpd seems to comply
with section 3.2.
How-To-Repeat:
1. Fresh install of OpenBSD 5.2 (nothing special) on at least two hosts.
2. On these hosts: In /etc/dhcpd.conf edit the "hardware ethernet"
value of the "static-client" host definition to match the MAC address
of your client.
3. Start dhcpd on these hosts:
# /usr/sbin/dhcpd -d
4. Start a DHCP client without knowledge of any leases on the client
computer in the same subnet as the servers. I have not tried it in
combination with a DHCP relay.
For example on OpenBSD 5.0:
# pkill dhclient
# rm /var/db/dhclient.leases.<interface>
# dhclient <interface>
The output of each dhcpd should be something like this:
DHCPDISCOVER from 00:06:29:92:65:93 via vic0
DHCPOFFER on 192.168.1.200 to 00:06:29:92:65:93 via vic0
DHCPREQUEST for 192.168.1.200 from 00:06:29:92:65:93 via vic0
DHCPACK on 192.168.1.200 to 00:06:29:92:65:93 via vic0
A tcpdump should show the 'server identifier' option in the DHCPREQUEST
message.
I observed the described behaviour with a managed switch as a DHCP
client and with an old OpenBSD 5.0 client, but it might also happen
with other clients - maybe with every client.
Unfortunately I was not able to test it with an OpenBSD 5.2 client.
Fix:
I have not investigated it.
Regards
Andy
SENDBUG: dmesg attached.
SENDBUG: Feel free to delete or use the -D flag if they contain
sensitive information.
dmesg:
OpenBSD 5.2 (GENERIC) #278: Wed Aug 1 10:04:16 MDT 2012
dera...@i386.openbsd.org:/usr/src/sys/arch/i386/compile/GENERIC
cpu0: Intel(R) Core(TM)2 Duo CPU T7500 @ 2.20GHz ("GenuineIntel"
686-class) 2.20 GHz
cpu0:
FPU,V86,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CFLUSH,DS,ACPI,MMX,FXSR,SSE,SSE2,SS,NXE,LONG,SSE3,SSSE3,CX16,LAHF
real mem = 200798208 (191MB)
avail mem = 186671104 (178MB)
mainbus0 at root
bios0 at mainbus0: AT/286+ BIOS, date 12/18/08, BIOS32 rev. 0 @
0xfd780, SMBIOS rev. 2.4 @ 0xe4010 (45 entries)
bios0: vendor Phoenix Technologies LTD version "6.00" date 12/18/2008
bios0: VMware, Inc. VMware Virtual Platform
acpi0 at bios0: rev 2
acpi0: sleep states S0 S1 S4 S5
acpi0: tables DSDT FACP BOOT APIC MCFG SRAT
acpi0: wakeup devices PCI0(S3) USB_(S1) P2P0(S3) S1F0(S3) S2F0(S3)
S3F0(S3) S4F0(S3) S5F0(S3) S6F0(S3) S7F0(S3) S8F0(S3) S9F0(S3) Z00P(S3)
Z00Q(S3) Z00R(S3) Z00S(S3) Z00T(S3) Z00U(S3) Z00V(S3) Z00W(S3) Z00X(S3)
Z00Y(S3) Z00Z(S3) Z010(S3) Z011(S3) Z012(S3) Z013(S3) Z014(S3) Z015(S3)
Z016(S3) Z017(S3) Z018(S3) Z019(S3) Z01A(S3) Z01B(S3) P2P1(S3) S1F0(S3)
S2F0(S3) S3F0(S3) S4F0(S3) S5F0(S3) S6F0(S3) S7F0(S3) S8F0(S3) S9F0(S3)
Z00P(S3) Z00Q(S3) Z00R(S3) Z00S(S3) Z00T(S3) Z00U(S3) Z00V(S3) Z00W(S3)
Z00X(S3) Z00Y(S3) Z00Z(S3) Z010(S3) Z011(S3) Z012(S3) Z013(S3) Z014(S3)
Z015(S3) Z016(S3) Z017(S3) Z018(S3) Z019(S3) Z01A(S3) Z01B(S3) P2P2(S3)
S1F0(S3) S2F0(S3) S3F0(S3) S4F0(S3) S5F0(S3) S6F0(S3) S7F0(S3) S8F0(S3)
S9F0(S3) Z00P(S3) Z00Q(S3) Z00R(S3) Z00S(S3) Z00T(S3) Z00U(S3) Z00V(S3)
Z00W(S3) Z00X(S3) Z00Y(S3) Z00Z(S3) Z010(S3) Z011(S3) Z012(S3) Z013(S3)
Z014(S3) Z015(S3) Z016(S3) Z017(S3) Z018(S3) Z019(S3) Z01A(S3) Z01B(S3)
P2P3(S3) S1F0(S3) S2F0(S3) S3F0(S3) S4F0(S3) S5F0(S3) S6F0(S3) S7F0(S3)
S8F0(S3) S9F0(S3) Z00P(S3) Z00Q(S3) Z00R(S3) Z00S(S3) Z00T(S3) Z00U(S3)
Z00V(S3) Z00W(S3) Z00X(S3) Z00Y(S3) Z00Z(S3) Z010(S3) Z011(S3) Z012(S3)
Z013(S3) Z014(S3) Z015(S3) Z016(S3) Z017(S3) Z018(S3) Z019(S3) Z01A(S3)
Z01B(S3) PE40(S3) S1F0(S3) PE50(S3) S1F0(S3) PE60(S3) S1F0(S3) PE70(S3)
S1F0(S3) PE80(S3) S1F0(S3) PE90(S3) S1F0(S3) PEA0(S3) S1F0(S3) PEB0(S3)
S1F0(S3) PEC0(S3) S1F0(S3) PED0(S3) S1F0(S3) PEE0(S3) S1F0(S3) PE41(S3)
S1F0(S3) PE42(S3) S1F0(S3) PE43(S3) S1F0(S3) PE44(S3) S1F0(S3) PE45(S3)
S1F0(S3) PE46(S3) S1F0(S3) PE47(S3) S1F0(S3) PE51(S3) S1F0(S3) PE52(S3)
S1F0(S3) PE53(S3) S1F0(S3) PE54(S3) S1F0(S3) PE55(S3) S1F0(S3) PE56(S3)
S1F0(S3) PE57(S3) S1F0(S3) PE61(S3) S1F0(S3) PE62(S3) S1F0(S3) PE63(S3)
S1F0(S3) PE64(S3) S1F0(S3) PE65(S3) S1F0(S3) PE66(S3) S1F0(S3) PE67(S3)
S1F0(S3) PE71(S3) S1F0(S3) PE72(S3) S1F0(S3) PE73(S3) S1F0(S3) PE74(S3)
S1F0(S3) PE75(S3) S1F0(S3) PE76(S3) S1F0(S3) PE77(S3) S1F0(S3) PE81(S3)
S1F0(S3) PE82(S3) S1F0(S3) PE83(S3) S1F0(S3) PE84(S3) S1F0(S3) PE85(S3)
S1F0(S3) PE86(S3) S1F0(S3) PE87(S3) S1F0(S3) PE91(S3) S1F0(S3) PE92(S3)
S1F0(S3) PE93(S3) S1F0(S3) PE94(S3) S1F0(S3) PE95(S3) S1F0(S3) PE96(S3)
S1F0(S3) PE97(S3) S1F0(S3) PEA1(S3) S1F0(S3) PEA2(S3) S1F0(S3) PEA3(S3)
S1F0(S3) PEA4(S3) S1F0(S3) PEA5(S3) S1F0(S3) PEA6(S3) S1F0(S3) PEA7(S3)
S1F0(S3) PEB1(S3) S1F0(S3) PEB2(S3) S1F0(S3) PEB3(S3) S1F0(S3) PEB4(S3)
S1F0(S3) PEB5(S3) S1F0(S3) PEB6(S3) S1F0(S3) PEB7(S3) S1F0(S3) SLPB(S4)
acpitimer0 at acpi0: 3579545 Hz, 24 bits
acpimadt0 at acpi0 addr 0xfee00000: PC-AT compat
cpu0 at mainbus0: apid 0 (boot processor)
cpu0: apic clock running at 67MHz
ioapic0 at mainbus0: apid 1 pa 0xfec00000, version 11, 24 pins
acpimcfg0 at acpi0 addr 0xe0000000, bus 0-255
acpiprt0 at acpi0: bus 0 (PCI0)
acpicpu0 at acpi0
acpibat0 at acpi0: BAT1 not present
acpibat1 at acpi0: BAT2 not present
acpiac0 at acpi0: AC unit online
acpibtn0 at acpi0: SLPB
bios0: ROM list: 0xc0000/0x8000 0xc8000/0x1000 0xdc000/0x4000!
0xe4000/0x4000!
vmt0 at mainbus0
pci0 at mainbus0 bus 0: configuration mode 1 (bios)
pchb0 at pci0 dev 0 function 0 "Intel 82443BX AGP" rev 0x01
ppb0 at pci0 dev 1 function 0 "Intel 82443BX AGP" rev 0x01
pci1 at ppb0 bus 1
piixpcib0 at pci0 dev 7 function 0 "Intel 82371AB PIIX4 ISA" rev 0x08
pciide0 at pci0 dev 7 function 1 "Intel 82371AB IDE" rev 0x01: DMA,
channel 0 configured to compatibility, channel 1 configured to
compatibility
wd0 at pciide0 channel 0 drive 0: <VMware Virtual IDE Hard Drive>
wd0: 64-sector PIO, LBA, 1024MB, 2097152 sectors
wd0(pciide0:0:0): using PIO mode 4, Ultra-DMA mode 2
atapiscsi0 at pciide0 channel 1 drive 0
scsibus0 at atapiscsi0: 2 targets
cd0 at scsibus0 targ 0 lun 0: <NECVMWar, VMware IDE CDR10, 1.00> ATAPI
5/cdrom removable
cd0(pciide0:1:0): using PIO mode 4, Ultra-DMA mode 2
piixpm0 at pci0 dev 7 function 3 "Intel 82371AB Power" rev 0x08: SMBus
disabled
"VMware Virtual Machine Communication Interface" rev 0x10 at pci0 dev 7
function 7 not configured
vga1 at pci0 dev 15 function 0 "VMware Virtual SVGA II" rev 0x00
wsdisplay0 at vga1 mux 1: console (80x25, vt100 emulation)
wsdisplay0: screen 1-5 added (80x25, vt100 emulation)
ppb1 at pci0 dev 17 function 0 "VMware Virtual PCI-PCI" rev 0x02
pci2 at ppb1 bus 2
vic0 at pci2 dev 0 function 0 "AMD 79c970 PCnet-PCI" rev 0x10: apic 1
int 18, address 00:0c:29:a4:5f:6e
eap0 at pci2 dev 1 function 0 "Ensoniq AudioPCI97" rev 0x02: apic 1 int
19
ac97: codec id 0x43525913 (Cirrus Logic CS4297A rev 3)
audio0 at eap0
midi0 at eap0: <AudioPCI MIDI UART>
ppb2 at pci0 dev 21 function 0 "VMware Virtual PCIE-PCIE" rev 0x01
pci3 at ppb2 bus 3
ppb3 at pci0 dev 21 function 1 "VMware Virtual PCIE-PCIE" rev 0x01
pci4 at ppb3 bus 4
ppb4 at pci0 dev 21 function 2 "VMware Virtual PCIE-PCIE" rev 0x01
pci5 at ppb4 bus 5
ppb5 at pci0 dev 21 function 3 "VMware Virtual PCIE-PCIE" rev 0x01
pci6 at ppb5 bus 6
ppb6 at pci0 dev 21 function 4 "VMware Virtual PCIE-PCIE" rev 0x01
pci7 at ppb6 bus 7
ppb7 at pci0 dev 21 function 5 "VMware Virtual PCIE-PCIE" rev 0x01
pci8 at ppb7 bus 8
ppb8 at pci0 dev 21 function 6 "VMware Virtual PCIE-PCIE" rev 0x01
pci9 at ppb8 bus 9
ppb9 at pci0 dev 21 function 7 "VMware Virtual PCIE-PCIE" rev 0x01
pci10 at ppb9 bus 10
ppb10 at pci0 dev 22 function 0 "VMware Virtual PCIE-PCIE" rev 0x01
pci11 at ppb10 bus 11
ppb11 at pci0 dev 22 function 1 "VMware Virtual PCIE-PCIE" rev 0x01
pci12 at ppb11 bus 12
ppb12 at pci0 dev 22 function 2 "VMware Virtual PCIE-PCIE" rev 0x01
pci13 at ppb12 bus 13
ppb13 at pci0 dev 22 function 3 "VMware Virtual PCIE-PCIE" rev 0x01
pci14 at ppb13 bus 14
ppb14 at pci0 dev 22 function 4 "VMware Virtual PCIE-PCIE" rev 0x01
pci15 at ppb14 bus 15
ppb15 at pci0 dev 22 function 5 "VMware Virtual PCIE-PCIE" rev 0x01
pci16 at ppb15 bus 16
ppb16 at pci0 dev 22 function 6 "VMware Virtual PCIE-PCIE" rev 0x01
pci17 at ppb16 bus 17
ppb17 at pci0 dev 22 function 7 "VMware Virtual PCIE-PCIE" rev 0x01
pci18 at ppb17 bus 18
ppb18 at pci0 dev 23 function 0 "VMware Virtual PCIE-PCIE" rev 0x01
pci19 at ppb18 bus 19
ppb19 at pci0 dev 23 function 1 "VMware Virtual PCIE-PCIE" rev 0x01
pci20 at ppb19 bus 20
ppb20 at pci0 dev 23 function 2 "VMware Virtual PCIE-PCIE" rev 0x01
pci21 at ppb20 bus 21
ppb21 at pci0 dev 23 function 3 "VMware Virtual PCIE-PCIE" rev 0x01
pci22 at ppb21 bus 22
ppb22 at pci0 dev 23 function 4 "VMware Virtual PCIE-PCIE" rev 0x01
pci23 at ppb22 bus 23
ppb23 at pci0 dev 23 function 5 "VMware Virtual PCIE-PCIE" rev 0x01
pci24 at ppb23 bus 24
ppb24 at pci0 dev 23 function 6 "VMware Virtual PCIE-PCIE" rev 0x01
pci25 at ppb24 bus 25
ppb25 at pci0 dev 23 function 7 "VMware Virtual PCIE-PCIE" rev 0x01
pci26 at ppb25 bus 26
ppb26 at pci0 dev 24 function 0 "VMware Virtual PCIE-PCIE" rev 0x01
pci27 at ppb26 bus 27
ppb27 at pci0 dev 24 function 1 "VMware Virtual PCIE-PCIE" rev 0x01
pci28 at ppb27 bus 28
ppb28 at pci0 dev 24 function 2 "VMware Virtual PCIE-PCIE" rev 0x01
pci29 at ppb28 bus 29
ppb29 at pci0 dev 24 function 3 "VMware Virtual PCIE-PCIE" rev 0x01
pci30 at ppb29 bus 30
ppb30 at pci0 dev 24 function 4 "VMware Virtual PCIE-PCIE" rev 0x01
pci31 at ppb30 bus 31
ppb31 at pci0 dev 24 function 5 "VMware Virtual PCIE-PCIE" rev 0x01
pci32 at ppb31 bus 32
ppb32 at pci0 dev 24 function 6 "VMware Virtual PCIE-PCIE" rev 0x01
pci33 at ppb32 bus 33
ppb33 at pci0 dev 24 function 7 "VMware Virtual PCIE-PCIE" rev 0x01
pci34 at ppb33 bus 34
isa0 at piixpcib0
isadma0 at isa0
com0 at isa0 port 0x3f8/8 irq 4: ns16550a, 16 byte fifo
com1 at isa0 port 0x2f8/8 irq 3: ns16550a, 16 byte fifo
pckbc0 at isa0 port 0x60/5
pckbd0 at pckbc0 (kbd slot)
pckbc0: using irq 1 for kbd slot
wskbd0 at pckbd0: console keyboard, using wsdisplay0
pms0 at pckbc0 (aux slot)
pckbc0: using irq 12 for aux slot
wsmouse0 at pms0 mux 0
pcppi0 at isa0 port 0x61
spkr0 at pcppi0
lpt0 at isa0 port 0x378/4 irq 7
npx0 at isa0 port 0xf0/16: reported by CPUID; using exception 16
fdc0 at isa0 port 0x3f0/6 irq 6 drq 2
mtrr: Pentium Pro MTRR support
vscsi0 at root
scsibus1 at vscsi0: 256 targets
softraid0 at root
scsibus2 at softraid0: 256 targets
root on wd0a (394db49dbb0c2646.a) swap on wd0b dump on wd0b
