| Summary: | Outbound UDP packets sometimes incorrectly sent on loopback interface | ||
|---|---|---|---|
| Product: | passt | Reporter: | David Gibson <dgibson> |
| Component: | UDP | Assignee: | nobody |
| Status: | RESOLVED INVALID | ||
| Severity: | normal | ||
| Priority: | Normal | ||
| Version: | unspecified | ||
| Hardware: | All | ||
| OS: | Linux | ||
It looks like this is because the sockets created for forwarding the output packets are bound to UNSPEC, meaning that when delivering to the host via gateway translation they use loopback. I based this on a misunderstanding of how the $GW translation is supposed to work. After discussing with Stefano the meaning of GW translation, the consensus was that $GW in the guest/ns represents the host's loopback address as seen from the host. There are still some weird edge cases with $GW translation, but this specific example is working as intended. |
# Steps to reproduce Assume $HOST is the host IP address and $GW is the gateway address: 1. On host, run: $ socat -u UDP4-LISTEN:2000,bind=$HOST STDOUT 2. On host, run: $ tcpdump -i lo 3. On host, run: $ pasta --config-net 4. Within pasta shell run: # echo hello | socat -u STDIN UDP4:$GW:2000 # Expected results "hello" appears on socat from step (1). tcpdump at (2) shows no packets related to this operation. # Actual results No output on the host listening socat, UDP packet with "hello" appears on the host loopback interface.