Finding the local address used on a multihomed network

Question

I am running a TCP/IP server and binding it to INADDR_ANY (0.0.0.0). My network is multi-homed so has multiple local IP addresses. So by using INADDR_ANY, the client can connect to me using any of those local addresses.

I now want to construct a full url with my local IP address. I will send this address to the client and (assuming no NAT-traversal), the client should be able to use the sent address to connect to my server. What socket API can I use to find this address? This address has to be used in the IP packet, so should be discoverable.

Does this answer your question - https://stackoverflow.com/a/3909936/12396017 ? I mean ```getifaddrs``` — Maxim Sagaydachny, Feb 06 '20 at 16:54

score 0 · Answer 1 · answered Feb 06 '20 at 17:32

0

There is no common socket API function across platforms for this type of query. You have to use OS-specific APIs instead.

On 'Nix platforms, you can use getifaddrs().
On Windows, you can use GetAdaptersInfo() (XP and earlier), GetAdaptersAddresses() (Vista and later), or WSAIoctl(SIO_GET_INTERFACE_LIST/_EX).
And so on.

answered Feb 06 '20 at 17:32

Remy Lebeau

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getifaddrs etc will give me all the my ip addresses, I however need to find out the one used by the remote end currently connecting to me – doron Feb 07 '20 at 11:59
@doron if a client is already connected to your TCP server, then `accept()` and `getpeername()` give you the client's IP, and `getsockname()` on the socket returned by `accept()` gives you the IP the client connected to. But if the client is already connected, why do you need to send a URL to the client to connect to? If the client needs to make a secondary connection to your server, it can just use the same IP it already used earlier. Your question doesn't make sense. Please clarify your scenario. – Remy Lebeau Feb 07 '20 at 18:01

Finding the local address used on a multihomed network

1 Answers1