google/dranet

Duplicate IPv6 routes found for interfaces using IPv6

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#274 opened on Nov 5, 2025

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bughelp wanted

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Description

Thanks to @liuyuan10 for spotting that there a scenario which is leading to presence of duplicate routes in the pod's namespace:

fd36::3:0:e:0:0/96 dev gpu0rdma2 proto kernel metric 256 pref medium
fd36::3:0:e:0:0/96 dev gpu0rdma2 metric 1024 pref medium

The behavior is only observed for interfaces with an IPv6 address that represents a subnet (rather than a complete /128). In this case, the kernel likely automatically creates a route for the IPv6 address that represents the subnet, e.g. the /96 above

Contributor guide

Research direction
Investigate how the kernel automatically creates routes for IPv6 subnet addresses on interfaces and identify why duplicate routes are generated. Trace the route addition code path in the driver to understand where the manual route overlaps with the kernel's automatic route.
Tech stack
go
Domain
backendnetworkinginfrastructure
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
GoKubernetesIPv6 networking
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
45