使用GRE隧道之后无法获取traceroute信息？

如题。

[root@lab1-cn ~]# ping api.twitter.com
PING api.twitter.com (199.59.149.232) 56(84) bytes of data.
64 bytes from api.twitter.com (199.59.149.232): icmp_seq=1 ttl=248 time=253 ms
64 bytes from api.twitter.com (199.59.149.232): icmp_seq=2 ttl=248 time=252 ms
64 bytes from api.twitter.com (199.59.149.232): icmp_seq=3 ttl=248 time=254 ms
64 bytes from api.twitter.com (199.59.149.232): icmp_seq=4 ttl=248 time=258 ms
64 bytes from api.twitter.com (199.59.149.232): icmp_seq=5 ttl=248 time=255 ms
64 bytes from api.twitter.com (199.59.149.232): icmp_seq=6 ttl=248 time=255 ms

--- api.twitter.com ping statistics ---
6 packets transmitted, 6 received, 0% packet loss, time 5001ms
rtt min/avg/max/mdev = 252.721/255.177/258.390/1.843 ms

[root@lab1-cn ~]# traceroute api.twitter.com
traceroute to api.twitter.com (199.59.149.232), 30 hops max, 40 byte packets
1 * * *
2 * * *
3 * * *
4 * * *
5 * * *
6 *

[root@lab1-cn ~]# route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
10.100.0.2 * 255.255.255.255 UH 0 0 0 tun0
10.100.0.2 * 255.255.255.255 UH 0 0 0 tun1
google-public-d * 255.255.255.255 UH 0 0 0 t0
100.100.100.0 * 255.255.255.0 U 0 0 0 t0
100.100.200.0 * 255.255.255.0 U 0 0 0 t1
199.59.148.0 * 255.255.252.0 U 0 0 0 t1
199.59.148.0 * 255.255.252.0 U 0 0 0 t0
110.76.44.0 * 255.255.252.0 U 0 0 0 eth1
10.100.0.0 10.100.0.2 255.255.0.0 UG 0 0 0 tun0
169.254.0.0 * 255.255.0.0 U 0 0 0 eth1
default 110.76.47.254 0.0.0.0 UG 0 0 0 eth1

[root@lab1-cn ~]# ifconfig
t0 Link encap:UNSPEC HWaddr 6E-4C-2F-69-00-00-00-00-00-00-00-00-00-00-00-00
inet addr:100.100.100.100 P-t-P:100.100.100.100 Mask:255.255.255.0
UP POINTOPOINT RUNNING NOARP MTU:1476 Metric:1
RX packets:44021 errors:0 dropped:0 overruns:0 frame:0
TX packets:41938 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:42076937 (40.1 MiB) TX bytes:6099836 (5.8 MiB)

t1 Link encap:UNSPEC HWaddr 6E-4C-2F-69-00-00-00-00-00-00-00-00-00-00-00-00
inet addr:100.100.200.100 P-t-P:100.100.200.100 Mask:255.255.255.0
UP POINTOPOINT RUNNING NOARP MTU:1476 Metric:1
RX packets:16294 errors:0 dropped:0 overruns:0 frame:0
TX packets:12876 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:20032748 (19.1 MiB) TX bytes:1415587 (1.3 MiB)