Carp: checksum failed on em0

[Ruben van der Zwan]

Hi all,

I have 2 routers running carp:

router1:
    ifconfig_carp0="vhid 1 pass hYYgtsRE 192.168.1.1/24"
    ifconfig_carp0_alias0="vhid 1 pass hYYgtsRE 192.168.2.1/24"
router2:
    ifconfig_carp0="vhid 1 advskew 100 pass hYYgtsRE 192.168.1.1/24"
    ifconfig_carp0_alias0="vhid 1 advskew 100 pass hYYgtsRE 192.168.2.1/24"

There are vlan's present on the routers, but the 192.168.1.2/2.2 for 
router1 and 192.168.1.3/2.3 for router2 IP addresses are present on an 
em0 interface.

/var/log/messages (on both router1 and router2) is flooded with these 
messages:
    Mar  8 21:53:58 router1 kernel: carp_input: checksum failed on em0
    Mar  8 21:53:58 router1 kernel: carp_input: received len 20 < 
sizeof(struct carp_header)
once every second...

I've tried to remove the alias on the carp0 interface, but this had no 
effect.
The servers are Dell PowerEdge SC1425 with a single Xeon configuration, 
HT is off:

FreeBSD 5.4-RELEASE-p11 #2: Mon Feb  6 11:14:13 UTC 2006
    root at router1.m0z.net:/usr/obj/usr/src/sys/CUSTOM
Timecounter "i8254" frequency 1193182 Hz quality 0
CPU: Intel(R) Xeon(TM) CPU 2.80GHz (2800.11-MHz 686-class CPU)
  Origin = "GenuineIntel"  Id = 0xf43  Stepping = 3
  
Features=0xbfebfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CLFLUSH,DTS,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT,TM,PBE>
real memory  = 1073479680 (1023 MB)
avail memory = 1040941056 (992 MB)
ACPI APIC Table: <DELL   PESC1425>
[....]
em0: <Intel(R) PRO/1000 Network Connection, Version - 1.7.35> port 
0xecc0-0xecff mem 0xfeae0000-0xfeafffff irq 32 at device 4.0 on pci2
em0: Ethernet address: 00:41:44:c4:52:22
em0:  Speed:N/A  Duplex:N/A
pcib3: <ACPI PCI-PCI bridge> at device 0.2 on pci1
pci3: <ACPI PCI bus> on pcib3

lspci:
00:00.0 Host bridge: Intel Corporation E7520 Memory Controller Hub (rev 09)
00:02.0 PCI bridge: Intel Corporation E7525/E7520/E7320 PCI Express Port 
A (rev 09)
00:1e.0 PCI bridge: Intel Corporation 82801 PCI Bridge (rev c2)
00:1f.0 ISA bridge: Intel Corporation 82801EB/ER (ICH5/ICH5R) LPC 
Interface Bridge (rev 02)
00:1f.1 IDE interface: Intel Corporation 82801EB/ER (ICH5/ICH5R) IDE 
Controller (rev 02)
01:00.0 PCI bridge: Intel Corporation 6700PXH PCI Express-to-PCI Bridge 
A (rev 09)
01:00.2 PCI bridge: Intel Corporation 6700PXH PCI Express-to-PCI Bridge 
B (rev 09)
02:04.0 Ethernet controller: Intel Corporation 82541GI/PI Gigabit 
Ethernet Controller (rev 05)
03:07.0 RAID bus controller: Promise Technology, Inc. PDC20571 (FastTrak 
TX2200) (rev 02)
04:03.0 Ethernet controller: Intel Corporation 82541GI/PI Gigabit 
Ethernet Controller (rev 05)
04:0d.0 VGA compatible controller: ATI Technologies Inc Radeon RV100 QY 
[Radeon 7000/VE]

It seems CARP is running fine, the first router has the shared IP, but 
two lines every second in /var/log/messages makes other debugging 
virtually impossible....
Does anybody know what's causing this messages and what I can do to stop 
them?