Comprehensive and Detailed Step-by-Step Explanation:
1. What is GRE (Generic Routing Encapsulation)?
* GRE is a tunneling protocol that allows the encapsulation of various types of packets (e.g., IPv4, IPv6, multicast, etc.) to be transmitted over another protocol (e.g., IP).
* GRE is used to create point-to-point connections over heterogeneous networks.
2. Analysis of Each Option:
Option A: GRE is a Layer 2 VPN encapsulation technology.
* Incorrect.
* GRE operates at Layer 3 (Network Layer) and encapsulates Layer 3 packets. It is not a Layer 2 VPN encapsulation technology like MPLS or Ethernet-over-IP.
Option B: GRE enables encapsulated data packets to be transmitted over another network layer protocol, but cannot encapsulate multicast data.
* Incorrect.
* GRE supports the encapsulation and transmission of multicast data packets. This is one of its key features, making it suitable for protocols like OSPF and multicast applications.
Option C: GRE tunnels can work with IPsec to ensure the security of multicast services such as voice and video.
* Correct.
* GRE by itself does not provide encryption or security. However, GRE can work with IPsec to secure the encapsulated traffic, including multicast data, for services like voice and video.
Option D: GRE tunnels can extend the working range of network protocols with hop limits.
* Correct.
* GRE encapsulates packets, effectively resetting their hop limits and allowing protocols with limited hop counts (e.g., RIP) to work over larger networks.
3. Summary:
* The correct options are C and D.
Reference:
Huawei HCIA-Datacom Study Guide, Chapter "GRE Tunnel Technology."
RFC 2784: Generic Routing Encapsulation (GRE).