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Thursday, November 01, 2012

Windows Virtual PC IPv6: Part 2

In the previous post we saw the wireless card was responsible for some IPv6 connectivity issues between a Windows XP Virtual PC and the Internet due to it rewriting the VPC virtual MAC address to the MAC address of the HOST.

Suspecting the wireless card may be the culprit, I physically connected the HOST to the switch on the router and changed the VPC settings to use the wired NIC instead of the wireless one. A quick reset and back to testing - this time in somewhat reverse order.

I first checked the router to see what the MAC address for the VPC was. It was correct!

ROUTER# arp -a
? ( at C4:17:FE:12:7D:75 [ether]  on br0
? ( at 00:03:FF:13:7D:75 [ether]  on br0

So I started my 'tcpdump' captures and launched the pings from the VPC.

HOST> tcpdump -i2 -nevvXX icmp or icmp6
00:03:ff:13:7d:75 > 58:6d:8f:78:ad:40, ethertype IPv6 (0x86dd),
length 94: (hlim 128, next-header: ICMPv6 (58), length: 40)
2001:db8:192:168:203:FFFF:FE13:7D75 > 2607:F8B0:400C:C03::68
[icmp6 sum ok] ICMP6, echo request, length 40, seq 553
  0x0000:  586d 8f78 ad40 0003 ff13 7d75 86dd 6000  Xm.x.@....}u..`.
  0x0010:  0000 0028 3a80 2001 0db8 0192 0168 0203  ...(:....p...|..
  0x0020:  ffff fe13 7d75 2607 f8b0 400c 0c03 0000  ....}u&...@.....
  0x0030:  0000 0000 0068 8000 9120 0000 0229 6162  .....h.......)ab
  0x0040:  6364 6566 6768 696a 6b6c 6d6e 6f70 7172  cdefghijklmnopqr
  0x0050:  7374 7576 7761 6263 6465 6667 6869       stuvwabcdefghi
00:03:ff:13:7d:75 > 58:6d:8f:78:ad:40, ethertype IPv4 (0x0800),
length 74: (tos 0x0, ttl 128, id 25380, offset 0, flags [none], 
proto: ICMP (1), length: 60) >
ICMP echo request, id 512, seq 9728, length 40
  0x0000:  586d 8f78 ad40 0003 ff13 7d75 0800 4500  Xm.x.@....}u..E.
  0x0010:  003c 6324 0000 8001 ddbe c0a8 0a68 4a7d  .< c$.........hJ}
  0x0020:  e450 0800 255c 0200 2600 6162 6364 6566  .P..%\..&.abcdef
  0x0030:  6768 696a 6b6c 6d6e 6f70 7172 7374 7576  ghijklmnopqrstuv
  0x0040:  7761 6263 6465 6667 6869                 wabcdefghi

The two packets show the IPv6 and IPv4 pings (echo requests) respectively. Notice the first line of each packet has the VPC source MAC address - '00:03:ff:13:7d:75' - not the HOST MAC address as seen in the previous test on the wireless card.

And the satisfying result:

VM> ping 2607:f8b0:400c:c03::68
Reply from 2607:f8b0:400c:c03::68: time=50ms

VM> ping
Reply from bytes=32 time=166ms TTL=52

Just to make sure this whole testing regime wasn't an anomaly, I rebooted and reset to my wireless configuration and tested again with same failed results described in the previous post.

Why do the wireless and wired cards behave differently? I haven't answered that yet. Certainly, they are from different manufacturers and have different settings as verified in the "Properties" page, "Configure..." button, "Advanced" tab of each adapter. I did verify the common settings were matched between cards. I have some more research to do to get to the bottom of this one.

So, "does Windows Virtual PC support IPv6?" It's complicated. As we've seen, it depends on the application, the host and virtual machine operating systems, and in this case, the hardware used.

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