Hi - does anyone know the significance of the 'fast tunneling enabled' comment in the show interface tunnel'x' output below:

Tunnel120 is up, line protocol is up

Hardware is Tunnel

Description:

Interface is unnumbered. Using address of Loopback100 (x.x.90.101)

MTU 1514 bytes, BW 256 Kbit, DLY 500000 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation TUNNEL, loopback not set

Keepalive set (5 sec), retries 3

Tunnel source x.x.91.133 (Loopback50), destination x.x.136.19

Tunnel protocol/transport GRE/IP, key disabled, sequencing disabled

Tunnel TTL 255

Checksumming of packets disabled, fast tunneling enabled

Last input never, output 00:00:03, output hang never

Last clearing of "show interface" counters never

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 2

Queueing strategy: fifo

Output queue: 0/0 (size/max)

5 minute input rate 0 bits/sec, 0 packets/sec

5 minute output rate 0 bits/sec, 0 packets/sec

3630570 packets input, 174267377 bytes, 0 no buffer

Received 0 broadcasts, 0 runts, 0 giants, 0 throttles

0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort

3641995 packets output, 175165679 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

0 output buffer failures, 0 output buffers swapped ou