28 lines
1.1 KiB
Markdown
28 lines
1.1 KiB
Markdown
---
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tags: [networks, VPN]
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created: Monday, February 24, 2025
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---
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# Network tunnels
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A network tunnel is a
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[Transport Layer](./Transport_Layer_of_Internet_Protocol.md) mechanism whereby
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data packets can travel across a network they would otherwise not be able to
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access. Similarly how an underground physical tunnel can be use to travel across
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an inaccessible geographic region.
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It is a broad concept of which there are various specific instances. However
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many involve creating a tunnel by wrapping a packet that cannot traverse a given
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network within the payload of a packet that can.
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For instance, an organisation may use [IPv6](./IP_addresses.md) addresses but
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want to send them over an IPv4 network. To achieve this they would enclose the
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packets within IPv4 packets.
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Similarly the scenario of a VPN. A user with a UK IP address wants to access a
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server in the US that has a firewall blocking non-US IPs. The user can bypass
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this restriction by connecting to a VPN running US servers. The UK packets are
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transferred under the aegis of the VPN's US IP.
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For more detail see
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[How tunnelling works with VPNs](./How_tunneling_works_with_VPNs.md).
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