03-20-2008 08:57 AM - edited 03-03-2019 09:13 PM
Tunnel1 is up, line protocol is up
Hardware is Tunnel
Internet address is 172.16.101.109/24
MTU 1514 bytes, BW 1000 Kbit, DLY 10000 usec,
reliability 255/255, txload 2/255, rxload 1/255
Encapsulation TUNNEL, loopback not set
Keepalive not set
Tunnel source 72.169.239.134 (FastEthernet0), destination UNKNOWN
Tunnel protocol/transport multi-GRE/IP
Key 0x186A0, sequencing disabled
Checksumming of packets disabled
Tunnel TTL 255
Fast tunneling enabled
Tunnel transmit bandwidth 8000 (kbps)
Tunnel receive bandwidth 8000 (kbps)
Tunnel protection via IPSec (profile "vpnprof")
Last input 00:00:00, output 00:00:00, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/0 (size/max)
5 minute input rate 4000 bits/sec, 4 packets/sec
5 minute output rate 8000 bits/sec, 6 packets/sec
7165427 packets input, 1206831456 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
8165531 packets output, 1473160831 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 output buffer failures, 0 output buffers swapped out
NVI0 is up, line protocol is up
03-20-2008 09:29 AM
mahesh
In general when IOS says that an interface is up and line protocol is up it means that the IOS believes that the interface is functioning properly and will correctly send and receive traffic. Part of the determination of this is the successful sending and receiving of keepalive messages.
But GRE tunnels are a bit different. In particular GRE tunnels do not perform keepalives by default. This is confirmed by this line of your output:
Keepalive not set
So for the GRE tunnel the indication of up/up indicates that the router believes that it can successfully get to the next hop address on the way to the tunnel destination (and since this appears to be a multipoint GRE tunnel there is potentially more than one destination address):
Tunnel protocol/transport multi-GRE/IP
So this router believes that tunnel 1 if functioning and can send and receive traffic.
HTH
Rick
03-20-2008 09:40 AM
thanks for ur reply
so is the interface Tunnel1 a logical interface or physical interface ?
03-20-2008 09:45 AM
Tunnels are always logical interfaces.
03-20-2008 09:48 AM
so the address
Internet address is 172.16.101.109/24
is address of ligical interface of the tunnel?
03-20-2008 09:52 AM
That is the IP address of the tunnel. All communications that pass through the tunnel (not the tunnel itself, just the communications that pass through the tunnel) use that IP address on that end of the tunnel, ie the next/previous hop for routers on the other end of the tunnel when going to/from networks connected to the router this configuration is from.
03-20-2008 10:03 AM
Tunnel source 72.169.239.134 (FastEthernet0), and this is source ip
of tunnel.
so what is difference between ip of tunnel
itself and souce ip of tunnel?
03-20-2008 10:12 AM
mahesh
The IP address of the tunnel (172.16.101.109) would be the source address used for any packet generated by the tunnel interface (for example if you ping the remote end of the tunnel the source address would be your tunnel interface address (172.16.101.109) and the destination address would be the tunnel address of the other end of the tunnel.
The source address of the tunnel (72.169.239.134) is the address of the tunnel packet as it is sent out the physical interface. If some packet came to the router to be forwarded it would have its own source and destination addresses. If that packet were to be forwarded through the tunnel interface then what GRE does is to encapsulate the original IP packet in a new IP header. In the new IP header the source address is the tunnel source address (72.169.239.134).
HTH
Rick
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