System.Net.IPNetwork - not working

[suchoss]

Description

System.Net.IPNetwork seems to be broken. It doesn`t work and always throws an exception: "System.FormatException: An invalid IP network was specified."

Reproduction Steps

//this IPNetwork works
var works = Microsoft.AspNetCore.HttpOverrides.IPNetwork.Parse("192.168.1.1/24");
//this IPNetwork doesnt work
var doesntWork = System.Net.IPNetwork.Parse("192.168.1.1/24");

Expected behavior

I would expect that this wont throw any exception var doesntWork = System.Net.IPNetwork.Parse("192.168.1.1/24");

Actual behavior

I am getting System.FormatException: An invalid IP network was specified. exception. And I am confused how to use this System.Net.IPNetwork

Regression?

No response

Known Workarounds

No response

Configuration

dotnet 8.0.100
Apple M1 Pro
macOS 14.1.1

But we tested it even on windows machine and we are getting the same results.

Other information

When I tried to step into (limited functionality on MacOS) i found this issue The specified baseAddress has non-zero bits after the network prefix. (Parameter 'baseAddress')

Tagging subscribers to this area: @dotnet/ncl
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Description

System.Net.IPNetwork seems to be broken. It doesn`t work and always throws an exception: "System.FormatException: An invalid IP network was specified."

Reproduction Steps

//this IPNetwork works
var works = Microsoft.AspNetCore.HttpOverrides.IPNetwork.Parse("192.168.1.1/24");
//this IPNetwork doesnt work
var doesntWork = System.Net.IPNetwork.Parse("192.168.1.1/24");

Expected behavior

I would expect that this wont throw any exception var doesntWork = System.Net.IPNetwork.Parse("192.168.1.1/24");

Actual behavior

I am getting System.FormatException: An invalid IP network was specified. exception. And I am confused how to use this System.Net.IPNetwork

Regression?

No response

Known Workarounds

No response

Configuration

dotnet 8.0.100
Apple M1 Pro
macOS 14.1.1

But we tested it even on windows machine and we are getting the same results.

Other information

When I tried to step into (limited functionality on MacOS) i found this issue The specified baseAddress has non-zero bits after the network prefix. (Parameter 'baseAddress')

Author:	suchoss
Assignees:	-
Labels:	area-System.Net
Milestone:	-

[MihaZupan]

See https://learn.microsoft.com/dotnet/api/system.net.ipnetwork#remarks

This type disallows arbitrary IP-address/prefix-length CIDR pairs. BaseAddress must be defined so that all bits after the network prefix are set to zero. In other words, BaseAddress is always the first usable address of the network. The constructor and the parsing methods will throw in case there are non-zero bits after the prefix.

In your case, that would mean that the input has to be 192.168.1.0/24 instead of 192.168.1.1/24

[suchoss]

@MihaZupan Thanks a lot. It helped.

[mishun]

Hi!
Apologies for bumping closed issue, but am I undestanding correctly that parsing inputs like 192.168.1.1/24 is currently basically impossible with IPNetwork? (and incidentally, getting IPNetwork from adapter's IP address and prefix length is pretty hard?)

[suchoss]

Sorry for the broad answer. From my understanding of the issue it works as following:

IP address is "a composite" of two addresses: Network address and computer address.

Network address is the left part of IP, computer address is the right part of IP.

E.g.
From 10.10.100.1 - you are not able to easily say which part is network address and which is computer address.
From 10.10.100.1/8 - you are able to say which part is network and which is computer since /8 says that the first 8 bits from the left is network address and the rest is computer address. But in order to have System.Net.IPNetwork working here, you need to have only Network address without computer address bits set. So it would have to be 10.0.0.0.

It is maybe a bit more understandable if you imagine it like bits.
10.10.100.1/8 => 00001010.00001010.01100100.00000001 => this is not going to be accepted by System.Net.IPNetwork, because after 8 bit from the left there are bits set to true (1)
10.0.0.0/8 => 00001010.00000000.00000000.00000000 => this will be ok for System.Net.IPNetwork there are only zeros after 8 bit from the left.

If you know network mask /x, then you can write your own parser using bitwise & operation to set right bits to zeros and then input it to System.Net.IPNetwork.

[mishun]

Wow, that's really nice explanation!

I looked the implementation up:

runtime/src/libraries/System.Net.Primitives/src/System/Net/IPNetwork.cs

Lines 180 to 201 in bacdea3

	public static bool TryParse(ReadOnlySpan<char> s, out IPNetwork result)
	{
	int separatorIndex = s.LastIndexOf('/');
	if (separatorIndex >= 0)
	{
	ReadOnlySpan<char> ipAddressSpan = s.Slice(0, separatorIndex);
	ReadOnlySpan<char> prefixLengthSpan = s.Slice(separatorIndex + 1);
	if (IPAddress.TryParse(ipAddressSpan, out IPAddress? address) &&
	int.TryParse(prefixLengthSpan, NumberStyles.None, CultureInfo.InvariantCulture, out int prefixLength) &&
	prefixLength <= GetMaxPrefixLength(address) &&
	!HasNonZeroBitsAfterNetworkPrefix(address, prefixLength))
	{
	Debug.Assert(prefixLength >= 0); // Parsing with NumberStyles.None should ensure that prefixLength is always non-negative.
	result = new IPNetwork(address, prefixLength, false);
	return true;
	}
	}
	result = default;
	return false;
	}

and it more or less confirms it.

Regarding 'can write your own parser' part, well, I was hoping to replace existing DIY stuff with IPNetwork. Frankly, pairs of ethernet interface address and network prefixe is probably the most common context CIDR string occur, so IPNetwork looks pretty much useless as is.