dotnet/AspNetCore.Docs · critical · InvalidOperationException

No suitable IP address.

Error message

No suitable IP address.

What it means

InvalidOperationException thrown after wildcard address substitution fails. When Kestrel is bound to a wildcard (0.0.0.0, [::], +, *) the code resolves a real IP via Dns.GetHostAddressesAsync(MachineName) and picks the first non-loopback IPv4 address. If none is found it throws because there is no concrete IP to point the HubConnection at.

Source

Thrown at aspnetcore/blazor/fundamentals/signalr.md:1877

        if (serverAddress is null)
        {
            throw new InvalidOperationException("No server address available.");
        }

        var uri = new UriBuilder(serverAddress + "/chathub");

        // If Kestrel is bound to a wildcard, substitute a real IP
        if (uri.Host is "0.0.0.0" or "[::]" or "+" or "*")
        {
            var addresses = await Dns.GetHostAddressesAsync(
                System.Environment.MachineName);
            var ip = addresses.FirstOrDefault(a =>
                a.AddressFamily == AddressFamily.InterNetwork
                && !IPAddress.IsLoopback(a));

            if (ip is null)
            {
                throw new InvalidOperationException("No suitable IP address.");
            }

            uri.Host = ip.ToString();
        }

        hubConnection = new HubConnectionBuilder()
            .WithUrl(uri.Uri)
            .Build();

        hubConnection.On<ChatMessage>("ReceiveMessage", (message) =>
        {
            ...
        });

        await hubConnection.StartAsync();
    }
}
```

View on GitHub (pinned to c67a80103a)

Solutions

1. Configure the hub base URL explicitly via configuration rather than resolving from MachineName.
2. Bind Kestrel to a specific IP instead of a wildcard so no substitution is needed.
3. Relax the filter to also accept IPv6 (AddressFamily.InterNetworkV6) when the host is IPv6-capable.
4. Ensure the hostname resolves to a non-loopback address (DNS/hosts file) before running.

Example fix

// before
var ip = addresses.FirstOrDefault(a =>
    a.AddressFamily == AddressFamily.InterNetwork
    && !IPAddress.IsLoopback(a));

if (ip is null)
{
    throw new InvalidOperationException("No suitable IP address.");
}

// after — accept IPv4 or IPv6, fall back to config
var ip = addresses.FirstOrDefault(a =>
        (a.AddressFamily == AddressFamily.InterNetwork
         || a.AddressFamily == AddressFamily.InterNetworkV6)
        && !IPAddress.IsLoopback(a));

if (ip is null)
{
    var configured = builder.Configuration["HubHostIp"];
    if (string.IsNullOrWhiteSpace(configured)
        || !IPAddress.TryParse(configured, out var parsed))
    {
        throw new InvalidOperationException(
            "No suitable IP address. Set 'HubHostIp' in configuration.");
    }
    ip = parsed;
}

var addresses = await Dns.GetHostAddressesAsync(Environment.MachineName);
var ip = addresses.FirstOrDefault(a =>
    (a.AddressFamily is AddressFamily.InterNetwork or AddressFamily.InterNetworkV6)
    && !IPAddress.IsLoopback(a));
if (ip is null && IPAddress.TryParse(Configuration["HubHostIp"], out var cfg)) ip = cfg;

static bool HasNonLoopbackIPv4(IPAddress[] addrs) =>
    addrs.Any(a => a.AddressFamily == AddressFamily.InterNetwork && !IPAddress.IsLoopback(a));

try { /* resolve IP */ }
catch (InvalidOperationException ex) when (ex.Message.Contains("suitable IP"))
{
    logger.LogError(ex, "No suitable host IP; set HubHostIp in configuration.");
}

When it happens

Trigger: Containerized or sandboxed host where DNS resolution of MachineName returns only loopback (127.0.0.1) or only IPv6 addresses; machines whose hostname does not resolve to an IPv4 address; environments where GetHostAddressesAsync returns an empty list.

Common situations: Running in Docker/Kubernetes with a hostname that does not resolve on the container network; CI runners with minimal networking; binding Kestrel to '+' on a host with no external IPv4 interface; IPv6-only hosts.

Related errors

• No server address available.
• Unable to bind DOM element: ${id}
• QR code size must be less than {MaxQrSize}.
• worker exports not loaded
• Unknown command: ${e.data.command}

AI-assisted analysis of dotnet/AspNetCore.Docs@c67a80103a (2026-08-13). Data as JSON: /api/errors/d0f19d8a981da3dc. Report an issue: GitHub.