Equal Cost Multi-path Routing

[fujiapple852]

Tracking issue for all Equal Cost Multi-path Routing work items.

We wish to support the following multi-path strategies:

• Classic (traceroute and MTR)
  • Set the sequence number in either the src or dest port number
• Paris (see here)
  • Use the IPv4 checksum field to store the sequence and manipulate the UDP payload to ensure a valid packet
• Dublin (see here)
  • Use the IPv4 identifier field to store the sequence number
  • Manipulate the IPv6 Payload Length to store the sequence number

We wish to support these for IPv4 & IPv6 for both UDP and TCP protocols.

Current support:

Strategy	Family	Protocol	Status
Classic	IPv4 / IPv6	UDP / TCP	✅
Paris	IPv4	UDP	✅
Paris	IPv6	UDP	✅
Dublin	IPv4	UDP	✅
Dublin	IPv6	UDP	✅
Paris	IPv4	TCP	❌
Paris	IPv6	TCP	❌
Dublin	IPv4	TCP	❌
Dublin	IPv6	TCP	❌

Tasks

• Support Dublin multipath routing for IPv4/UDP #158
• Support Paris multipath routing for IPv4/UDP #542
• Support Dublin multipath strategy for IPv6/UDP #272
• Support Paris multipath routing for IPv6/UDP #749
• Detect NAT for udp/dublin strategy #1104

[crisidev]

In this tracking issue there is no mention of supporting Paris for IPv6. Is it something planned by any chance?

[fujiapple852]

@crisidev I'd certainly like for Trippy to be able to support the Paris ECMP strategy for IPv6/UDP.

I'm struggling to recall the details now but I know that when I initially added IPv6/UDP support to Trippy I hit some issues with IPv6/UDP checksum on Linux (may have been related to hardware offloading).

As a reminder: the Paris ECMP strategy works by manipulating the UDP checksum (and payload) to encode the sequence number in the checksum. In order to do this we need to be able to specify (or manipulate) the IPv6/UDP header.

It might be possible to set IP_HDRINCL (or perhaps IPV6_HDRINCL?) on the IPv6/UDP raw socket such that the correct checksum could be set, I'd have to try it again to see as a lot has changed since then. At the time I opened this GH issue I likely believed it was not possible. Digging into the libparistraceroute src code may also help point at the right solution.

Is using the Paris ECMP strategy for IPv6/UDP something you have experience with? I'm curious as to your use case for it.

[crisidev]

Thanks a lot for the detailed answer. I unfortunately do not have a lot of experience with Paris ECMP for IPv6/UDP. I have a pretty complex IPv6 home network I am currently experimenting using the official Paris traceroute, but I am well versed and love Rust, hence I would like to rewrite my probe code and base it on Trippy.

I just started scratching the surface of your amazing project, but when I have a little bit of time, I could try to reintroduce this support, after properly understanding how Paris traceroute does it in their library.

[fujiapple852]

@crisidev I managed to get it to work :)

Tested in Linux and macOS and seems to work. If you were able to try it out that would be great!

Issue #749 and WIP pr in #750

[crisidev]

Oh wow, that was fast! I'll try this out today!

[fujiapple852]

@crisidev Dublin for IPv6 just merged and will be in 0.10.0 if that's of interest to you.

[Pruthviraj1223]

Hello is there any update for Paris and Dublin support for TCP protocol ??? I am really interested into this and also I'm working on something where this will be very helpful

[fujiapple852]

@Pruthviraj1223 I'm afraid not.

This is one of the “big ticket” topics I listed a few months ago.

What makes this hard is that, for TCP, trippy operates at layer 7 rather than layer 3/4 due to various OS restrictions. I’d need to experiment, but it may not be possible without resorting to sending packets at layer 2 or using TAP/TUN or eBPF.

Certainly something I’m keep to support, but as it is nontrivial it’ll take time.

Aside: I’d be interested in hearing what you plan to use this for?