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For which reason can a GRE tunnel have an up down status?
The GRE tunnel status alternates between up and down if the outbound interface in the routes to the destination address of the tunnel interface is the local tunnel interface, or the neighbor device may advertise an incorrect route.
How much overhead does GRE add?
GRE does add an additional 24-byte header of overhead. This overhead contains a new 20-byte IP header, which indicates the source and destination IP addresses of the GRE tunnel. The remaining 4 bytes are the GRE header itself. Additional GRE options can increase the GRE header by up to another 12 bytes.
What does GRE Tunneling on a router mean?
What does GRE tunneling mean? Encapsulating packets within other packets is called “tunneling.” GRE tunnels are usually configured between two routers, with each router acting like one end of the tunnel. The routers are set up to send and receive GRE packets directly to each other.
What are the four states of a GRE tunnel interface?
There are four possible states in which a GRE tunnel interface can be: Up/up – This implies that the tunnel is fully functional and passes traffic. It is both administratively up and it’s protocol is up as well. Administratively down/down – This implies that the interface has been administratively shut down.
How does GRE Tunneling work for magic transit?
In order for Magic Transit to protect and accelerate customers’ network traffic, the Cloudflare network has to be securely connected to customers’ internal networks. For this purpose, GRE tunneling is extremely useful. Via GRE tunneling, Magic Transit is able to connect directly to Cloudflare customers’ networks securely over the public Internet.
Are there tunnel keepalives for multipoint GRE tunnels?
Tunnel keepalives are configurable on multipoint GRE (mGRE) tunnels but have no effect. Note: In general, tunnel keepalives will not work when VRFs are used on the tunnel interface and the fVRF (‘tunnel vrf …’) and iVRF (‘ip vrf forwarding …’ on tunnel interface) do not match.