[✨ Triage] dotnet/runtime#117114 by WeihanLi - `System.Net.IPNetwork` not behave as `Microsoft.AspNetCore.HttpOverri ...

[MihuBot]

Triage for dotnet/runtime#117114.
Repo filter: All networking issues.
MihuBot version: 0c3d2c.
Ping MihaZupan for any issues.

This is a test triage report generated by AI, aimed at helping the triage team quickly identify past issues/PRs that may be related.
Take any conclusions with a large grain of salt.

dotnet/runtime#117114: `System.Net.IPNetwork` not behave as `Microsoft.AspNetCore.HttpOverrides.IPNetwork` by WeihanLi
[Tool] Searching for System.Net.IPNetwork TryParse CIDR, Microsoft.AspNetCore.HttpOverrides.IPNetwork TryParse, System.Net.IPNetwork vs Microsoft.AspNetCore.HttpOverrides.IPNetwork, IPNetwork.TryParse 127.0.0.1/8, System.Net.IPNetwork parsing differences (IncludeOpen=True, IncludeClosed=True, IncludeIssues=True, IncludePullRequests=True, Repository=dotnet/runtime)
[Tool] Obtained 5 comments for issue #95321: System.Net.IPNetwork - not working
[Tool] Found 34 issues, 185 comments, 34 returned results (11738 ms)

Here are the most relevant related issues and discussions for triaging issue #117114 ("System.Net.IPNetwork not behave as Microsoft.AspNetCore.HttpOverrides.IPNetwork"):

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1. Issue #95321 (Nov 2023) - "System.Net.IPNetwork - not working"

• Summary: Reports that System.Net.IPNetwork.Parse("192.168.1.1/24") throws a FormatException, while Microsoft.AspNetCore.HttpOverrides.IPNetwork.Parse("192.168.1.1/24") works.
• Key Discussion:
  • MihaZupan (team): Explains that System.Net.IPNetwork requires the base address to have all host bits zeroed (i.e., must be the network address, not any address in the subnet). So, "192.168.1.0/24" is valid, but "192.168.1.1/24" is not.
  • Further comments: Users express that this makes System.Net.IPNetwork less useful for common scenarios, as CIDR strings often use a host address with a prefix.
  • Conclusion: This is by design for System.Net.IPNetwork to ensure unambiguous representation, but it is a breaking difference from the ASP.NET Core implementation.

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2. Issue #95865 (Dec 2023) - "System.Net.IPNetwork parse CIDR issue"

• Summary: User confused why IPNetwork.TryParse("2001:0db8::1/64", out var _) fails, but IPNetwork.TryParse("2001:0db8::/64", out var _) works.
• Key Discussion:
  • antonfirsov (team): Reiterates that the base address must have all bits after the prefix set to zero. The input must be the network address, not an arbitrary address in the subnet.
  • User acknowledges: The mistake was using a host address instead of the network address.
• Conclusion: Documentation and behavior are consistent with the design.

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3. Issue #79946 (Dec 2022–Jul 2023) - "[API Proposal]: Add a type to represent IP networks based on CIDR notation"

• Summary: This is the original API proposal and design discussion for adding System.Net.IPNetwork.
• Key Discussion:
  • The design intentionally disallows arbitrary IP/prefix pairs; the base address must be the network address (host bits zero).
  • This is different from the ASP.NET Core IPNetwork, which is more permissive.
  • The rationale is to ensure unambiguous representation and simplify equality and other operations.
  • There is explicit discussion about the difference from the ASP.NET Core implementation and the need to clarify/document this.
• Conclusion: The difference is intentional and by design.

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4. Issue #64033 (Jan–Feb 2022) - "API Proposal: IPNetwork to support CIDR notation"

• Summary: Early proposal to move the ASP.NET Core IPNetwork to System.Net.
• Key Discussion:
  • Triage at the time was that demand was not high enough, but this changed with #79946.
  • Notes that the ASP.NET Core version is more permissive.

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5. Issue #86584 (May 2023) - "[API Proposal]: Move IPNetwork to System.Net and add a string constructor"

• Summary: Suggests moving the ASP.NET Core IPNetwork to System.Net and making it more generally available.
• Key Discussion:
  • Team responds that System.Net.IPNetwork is being added in .NET 8, but with stricter parsing rules than the ASP.NET Core version.

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6. Issue #36428 (May–Jun 2020) - "Add CIDR Block logic to System.Net"

• Summary: Proposal for richer CIDR/subnet support in the BCL.
• Key Discussion:
  • Triage at the time was that this was too niche, but later demand led to the addition of System.Net.IPNetwork.

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7. Issue #96356 (Dec 2023) - "IpAddress subnetwork support"

• Summary: User asks about subnet mask verification.
• Key Discussion:
  • Team points to System.Net.IPNetwork as the solution, but with the caveat of its stricter requirements.

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8. Issue #104591 (Jul 2024) - "[API Proposal]: IpNetwork does not allow to check if another network is subnet of current network"

• Summary: User requests additional features for System.Net.IPNetwork, such as checking if one network contains another, and calculating broadcast/network addresses.
• Key Discussion:
  • No team response yet, but highlights ongoing interest in richer subnet/CIDR support.

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9. Issue #98427 (Feb–Jun 2024) - "IPNetwork.Contains for IPv4 networks should match IPv4-Mapped IPv6 Addresses"

• Summary: Discusses behavior of Contains for IPv4-mapped IPv6 addresses, not directly about parsing, but relevant for completeness.

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10. Issue #93022 (Sep–Oct 2023) - "The type 'IPNetwork' exists in both 'System.Net.IPNetwork' and 'System.Net.Primitives'"

• Summary: Reports a type name conflict when using the IPNetwork2 NuGet package and .NET 8+.

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Key Takeaways for Triaging

• The behavior difference between System.Net.IPNetwork and Microsoft.AspNetCore.HttpOverrides.IPNetwork is intentional and by design.
• System.Net.IPNetwork requires the base address to be the network address (all host bits zero), not just any address in the subnet. This is stricter than the ASP.NET Core version.
• This design is documented and was discussed at length in the API proposal (#79946).
• Users who want the more permissive behavior of the ASP.NET Core version will need to zero the host bits themselves before using System.Net.IPNetwork.
• There is ongoing interest in richer subnet/CIDR support, but the current behavior is not considered a bug.

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Most Directly Related Issues

• #95321: User confusion about why System.Net.IPNetwork fails to parse non-network addresses; team explains the design.
• #79946: API proposal and design rationale, including explicit discussion of the stricter parsing rules.
• #95865: Another example of user confusion, with team reiterating the design.
• #86584: Team clarifies the difference between the new BCL type and the ASP.NET Core version.

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If you need to reference a canonical answer for this triage, point to the remarks in the documentation and the explanations in #95321 and #79946. The difference is not a regression or bug, but a deliberate design choice for the BCL type.