About this interactive
A tunnel wraps a packet in an **extra Layer 3 header** at the tunnel's start. That header has its own source and destination (the two ends of the tunnel) and its own TTL. Every router along the way routes on it and ignores the packet inside. At the far end the extra header comes off, and the **original packet** is routed on as normal.
The lesson's letter: the letter in its addressed envelope is the original packet, and the outer envelope, addressed to the end of the tunnel, is the added header.
Uses from 0010: carrying OSPF between your routers across a provider that will not take part, tunneling guest Wi-Fi back to a controller. Tunnels between IP versions are practised in 0040's own set.
What you'll learn
- Distinguish a tunnel's added Layer 3 header from the packet's original header: which addresses each carries, who reads it and where it is removed
- Recognize why a tunnel is used: to carry traffic, such as a routing protocol, across a network that would not route it
Aligned to
Cisco CCNA
5.5
Describe IPsec remote access and site-to-site VPNs
1.2
Describe characteristics of network topology architectures
Key terms
- Encapsulation
- The process of wrapping data with protocol headers as it passes down the layers of the OSI model.
- Generic Routing Encapsulation
GRE
- A tunneling protocol developed by Cisco that encapsulates a wide variety of network layer protocols inside point-to-point virtual links, enabling the transport of protocols that would not normally be routable. GRE tunnels are stateless and do not provide encryption, so they are often combined with IPsec for secure VPN deployments.
Topics
Tunneling
Encapsulation
Gre
Ipv6 Over Ipv4
Wan
Interactive
Streak Sort
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