fundamental question on Winsock

[cyberninja]

If I use Winsock only as IPC (not RPC) by specifying the binding address as 127.0.0.1. (i.e. the local server listens to a port on 127.0.0.1 and the local client send messages to the port on 127.0.0.1. Is it possible for any firewall to block the communication?

I know the communication does not actually go through the physical layer, but I heard that some firewalls block data at higher layer (TCP or IP layer). I tested with Windows XP internal firewall and it does not block. However, I don't know if all firewalls do not block the local communication.

Thanks,

cyberninja

[sargon]

I have never seen a firewall that blocks the loopback address... just my 2¢

[Mathew Joy]

Well, it is possible. LSP for instance.

[cyberninja]

By replacing Winsock, it is possible...
There are lots of none-network apps binding 127.0.0.1 to a socket as IPC, so those apps will not work with LSP?

[cyberninja]

By using LSP, technically it is possible (even blocking the whole networks...).
Is there any existing filewall (may or may not implement LSP) provides the functionality of blocking the communication (127.0.0.1) on the same machine? I mean the communication is between two local process, rather than a "fake 127.0.0.1" from the network.

[Mathew Joy]

Well I think there is no firewall that uses LSP to filter, because non-winsock calls can bypass LSP layer. ZA started as an LSP though.

[cyberninja]

So I can assume that if winsock is used as IPC and listens to 127.0.0.1, I don't need to care about the blocking from a firewall.
Thanks,

cyberninja