- Developed by the IETF, GRE is a secure tunneling protocol that was designed for Cisco routers.
- By default, GRE does not include any flow control mechanisms.
- GRE provides encapsulation for a single protocol type that is traveling through the VPN.
- GRE tunnels support multicast traffic.
- GRE uses AES for encryption unless otherwise specified.
- GRE creates additional overhead for packets that are traveling through the VPN.
Explanation: GRE was developed by Cisco and encapsulates a wide variety of protocol packet types inside IP tunnels. GRE is stateless and does not include any flow control mechanisms by default. GRE is defined in an IETF standard. GRE does not include any strong security mechanisms to protect the traffic that crosses the site-to-site VPN. GRE supports routing protocols by using multicast traffic as a carrier protocol. GRE headers and the tunneling IP header create additional overhead for tunneled packets. GRE provides encapsulation for multiple protocol types inside an IP tunnel.
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