(usagi-users 02238) my 6to4 tunnel via gprs link doesn't work!!

[ke chen <iw01_cke@xxxxxxxxx>]

Hi, all
Can anyone give me a hand?
my 6to4 tunnel doesn't work, but once it works well. I just wonder what
happened.
I intend to construct the tunnel via gprs link. After connecting to the
gprs network, I can get a unique IPv4 address
#ifconfig ppp0
ppp0      Link encap:Point-to-Point Protocol
          inet addr:213.101.158.125  P-t-P:10.6.6.6  Mask:255.255.255.255
          UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1500  Metric:1
          RX packets:53 errors:0 dropped:0 overruns:0 frame:0
          TX packets:84 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:3
          RX bytes:8650 (8.4 Kb)  TX bytes:10326 (10.0 Kb)
#route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use
Iface
10.6.6.6        *               255.255.255.255 UH    0      0        0 ppp0
127.0.0.0       *               255.0.0.0       U     0      0        0 lo
default         10.6.6.6        0.0.0.0         UG    0      0        0 ppp0

#ip -6 addr show
1: lo: <LOOPBACK,UP> mtu 16436 qdisc noqueue
    inet6 ::1/128 scope host
5: eth1: <BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast qlen 100
    inet6 fe80::2e0:3ff:fe07:def7/10 scope link
7: 6to4@NONE: <POINTOPOINT,NOARP,UP> mtu 1480 qdisc noqueue
    inet6 fe80::d565:9e7d/128 scope link
    inet6 2002:d565:9e7d::1/64 scope global

#ip -6 route show
2002:d565:9e7d::/64 via :: dev 6to4  proto kernel  metric 256  mtu 1480
advmss 1420
2000::/3 dev 6to4  metric 1024  mtu 1480 advmss 1420
fe80::/10 dev eth1  proto kernel  metric 256  mtu 1500 advmss 1440
fe80::/10 via :: dev 6to4  proto kernel  metric 256  mtu 1480 advmss 1420
ff00::/8 dev eth1  proto kernel  metric 256  mtu 1500 advmss 1440
ff00::/8 dev 6to4  proto kernel  metric 256  mtu 1480 advmss 1420
unreachable default dev lo  metric -1  error -101

my linux kernel vervsion is 2.4.19, and I use the following scripts to
contruct the tunnel
ip -6 tunnel add 6to4 mode sit remote 192.88.99.1 local 213.101.158.125
ip link set dev 6to4 up
echo "1"> /proc/sys/net/ipv6/conf/6to4/forwarding
ip -6 addr add  2002:d565:9e7d::1/64 dev 6to4
ip -6 route add 2000::/3 dev 6to4

when execute ping6 www.kame.net, I got the result from tcpdump.
08:48:04.776973 213.101.158.125 > 192.88.99.1: 2002:d565:9e7d::1 >
2001:200:0:4819:210:f3ff:fe03:4d0: icmp6: echo request (encap)
08:48:05.016886 202.255.45.5 > 213.101.158.125:
2001:200:0:4819:210:f3ff:fe03:4d0 > 2002:d565:9e7d::1: icmp6: echo reply
(encap)
08:48:05.016923 213.101.158.125 > 202.255.45.5: icmp: 213.101.158.125
protocol 41 unreachable [tos 0xc0]

In fact, the packet has already succssfully being transferred through
the tunnel. When it came back to the ppp0 interface, there is something
wrong so that the V6 packet which is encapsulated into the V4 packet 
can't be decapsulate and send it to 6to4 interface.

Can anybody help me solve this problem?

Thanks in advance.

Best Regards,
  ke chen