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.
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.
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 (220.127.116.11) 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 (18.104.22.168).
We are pleased to announce availability of Beta software for 16.6.3.
16.6.3 will be the second rebuild on the 16.6 release train targeted
towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are
looking for early feedback from customers befor...
Introduction Featured Speakers Luis Espejel is the Telecommunications
Manager of IENova, an Oil & Gas company. Currently he works with Cisco
IOS® and Cisco IOS XE platforms, and NX to some extent. He has also
worked as a Senior Engineer with the Routing P...
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