Hello! I'm in the cisco 4006 switch configure netflow.

Hello! I'm in the cisco 4006 switch configure netflow. but show ip cache flow no date
configure :
config)>#ip flow-export version 5
config)>#ip flow-export destination 10.30.1.1 8888
config)>#interface vlan 3
config-if)>#ip route-cache flow

cisco 4006#sho ip cache flow
IP packet size distribution (0 total packets):
1-32 64 96 128 160 192 224 256 288 320 352 384 416 448 480
.000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000

512 544 576 1024 1536 2048 2560 3072 3584 4096 4608
.000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000

IP Flow Switching Cache, 278544 bytes
0 active, 4096 inactive, 0 added
0 ager polls, 0 flow alloc failures
Active flows timeout in 30 minutes
Inactive flows timeout in 15 seconds
last clearing of statistics never
Protocol Total Flows Packets Bytes Packets Active(Sec) Idle(Sec)
-------- Flows /Sec /Flow /Pkt /Sec /Flow /Flow

SrcIf SrcIPaddress DstIf DstIPaddress Pr SrcP DstP Pkts

Why??