Unable to ping guest from host in host-only network; ping6 works

[Rick]

An environment with a VM that has 2 types of networks: 1 NAT, 1 Host-Only
NAT works fine for world access but for internal access to the host, the IPv4 is not working even though IPv6 works fine

The host is running MacOSX 10.7.5
The Guest is an Ubuntu 11.10

Host virtual switches
vboxnet0: flags=8842<BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500

ether 0a:00:27:00:00:00

vboxnet1: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500

ether 0a:00:27:00:00:01
inet 10.100.100.1 netmask 0xffffff00 broadcast 10.100.100.255
inet6 fe80::800:27ff:fe00:1%vboxnet1 prefixlen 64 scopeid 0x9
inet6 2000:aaaa::1 prefixlen 64

Ping6 test from host to guest
nightwatch:~ ricky$ ping6 2000:aaaa::2
PING6(56=40+8+8 bytes) 2000:aaaa::1 --> 2000:aaaa::2
16 bytes from 2000:aaaa::2, icmp_seq=0 hlim=64 time=155.398 ms
16 bytes from 2000:aaaa::2, icmp_seq=1 hlim=64 time=0.715 ms
16 bytes from 2000:aaaa::2, icmp_seq=2 hlim=64 time=1.023 ms
16 bytes from 2000:aaaa::2, icmp_seq=3 hlim=64 time=0.840 ms
16 bytes from 2000:aaaa::2, icmp_seq=4 hlim=64 time=0.929 ms
16 bytes from 2000:aaaa::2, icmp_seq=5 hlim=64 time=0.875 ms
16 bytes from 2000:aaaa::2, icmp_seq=6 hlim=255 time=0.909 ms
16 bytes from 2000:aaaa::2, icmp_seq=7 hlim=255 time=0.873 ms
16 bytes from 2000:aaaa::2, icmp_seq=8 hlim=255 time=0.864 ms
16 bytes from 2000:aaaa::2, icmp_seq=9 hlim=255 time=0.739 ms
16 bytes from 2000:aaaa::2, icmp_seq=10 hlim=255 time=0.756 ms
16 bytes from 2000:aaaa::2, icmp_seq=11 hlim=255 time=1.067 ms
^{C
--- 2000:aaaa::2 ping6 statistics ---
12 packets transmitted, 12 packets received, 0.0% packet loss
round-trip min/avg/max/std-dev = 0.715/13.749/155.398/42.709 ms}

Ping Test from Host to Guest
nightwatch:~ ricky$ ping 10.100.100.2
PING 10.100.100.2 (10.100.100.2): 56 data bytes
Request timeout for icmp_seq 0
Request timeout for icmp_seq 1
^{C
--- 10.100.100.2 ping statistics ---
3 packets transmitted, 0 packets received, 100.0% packet loss
nightwatch:~ ricky$}

Guest Network Configuration
ricky@bunker:~$ ifconfig
eth0 Link encap:Ethernet HWaddr 08:00:27:41:4f:1b

inet addr:10.0.2.15 Bcast:10.0.2.255 Mask:255.255.255.0
inet6 addr: fe80::a00:27ff:fe41:4f1b/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:2 errors:0 dropped:0 overruns:0 frame:0
TX packets:29 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:1180 (1.1 KB) TX bytes:2240 (2.2 KB)

eth1 Link encap:Ethernet HWaddr 08:00:27:9d:08:1d

inet addr:10.100.100.2 Bcast:0.0.0.0 Mask:255.255.255.0
inet6 addr: fe80::a00:27ff:fe9d:81d/64 Scope:Link
inet6 addr: 2000:aaaa::2/64 Scope:Global
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:168 errors:0 dropped:0 overruns:0 frame:0
TX packets:238 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:20887 (20.8 KB) TX bytes:23841 (23.8 KB)

lo Link encap:Local Loopback

inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)

pimreg Link encap:UNSPEC HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00

UP RUNNING NOARP MTU:1472 Metric:1
RX packets:0 errors:0 dropped:0 overruns:0 frame:0
TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)

Ping6 Test from guest to Host
ricky@bunker:~$ ping6 2000:aaaa::1
PING 2000:aaaa::1(2000:aaaa::1) 56 data bytes
64 bytes from 2000:aaaa::1: icmp_seq=1 ttl=64 time=0.317 ms
64 bytes from 2000:aaaa::1: icmp_seq=2 ttl=64 time=0.518 ms
^C

2000:aaaa::1 ping statistics

2 packets transmitted, 2 received, 0% packet loss, time 1001ms
rtt min/avg/max/mdev = 0.317/0.417/0.518/0.102 ms
ricky@bunker:~$ ^C