Allow Linux optimizations (UDP GRO for forwarding) on multiple default interfaces and IPv6

[lmagyar]

Proposed Changes

SSIA

Related Issues

PR #351 #360

Summary by CodeRabbit

• New Features
  • Enhanced network interface handling to support UDP GRO forwarding, improving network performance.

[coderabbitai]

Walkthrough

The recent update enhances the network configuration by replacing the default_route_device variable with interface and iterating over all network interfaces. This change ensures that UDP Generic Receive Offload (GRO) forwarding is enabled for each interface using ethtool, improving overall network performance.

Changes

File Path	Change Summary
tailscale/.../s6-rc.d/post-tailscaled/run	Replaced default_route_device with interface and added iteration over network interfaces to enable UDP GRO forwarding with ethtool

🌟 In the land of code and bytes,
A rabbit hops through network lights,
With ethtool in its furry grip,
Interfaces now take a forward trip.
UDP GRO, swift and keen,
Hops along the digital stream.
🌐✨🐇

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[coderabbitai]

Actionable comments posted: 0

Review Details

Configuration used: CodeRabbit UI
Review profile: CHILL

Commits

Files that changed from the base of the PR and between a2684e5 and f3a303b.

Files selected for processing (1)

• tailscale/rootfs/etc/s6-overlay/s6-rc.d/post-tailscaled/run (2 hunks)

Additional comments not posted (2)

tailscale/rootfs/etc/s6-overlay/s6-rc.d/post-tailscaled/run (2)

7-7: The variable name change from default_route_device to interface is appropriate for handling multiple network interfaces.

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20-27: The loop correctly handles enabling UDP GRO on both IPv4 and IPv6 interfaces. Ensure that ethtool is installed on the system as it's crucial for these settings.

[frenck]

Thanks, @lmagyar 👍

../Frenck

[lmagyar]

And now I'm thinking why Tailscale suggested only the default interface?

That is good for exit nodes, but what about advertised subnets?

Shouldn't we do this optimization for the advertised subnets' interfaces also, like the MSS clamping?

[frenck]

I cannot answer that suggestion. If they explicitly suggest it as such, there must be some kind of reason for it on their end.

[lmagyar]

FYI: Certainly you are right, they check for the default interface only, for whatever reason. https://github.com/tailscale/tailscale/blob/main/ipn/ipnlocal/local.go#L5523