Dear Junos, Tunnels Are Not Virtual Links
Late June netlab added GRE tunnel support, including Junos, but integration tests with FRR containers exposed a Junos OSPFv3 failure because it incorrectly sent DBD packets over GRE tunnels with MTU set to zero, a behavior meant for virtual links.
MAIN POINTS
- netlab added GRE tunnel support in late June, including a Junos implementation.
- Initial testing appeared successful until GRE tunnels were tested between a device and FRR containers.
- Junos failed to form an OSPFv3 adjacency over GRE with FRR.
- Stefano Sasso traced the issue to Junos treating GRE tunnels like virtual links and using MTU zero for DBD packets.
TAKEAWAYS
- Integration tests can reveal interoperability issues that basic validation misses.
- GRE tunnel behavior may differ across vendors, especially in routing protocol handling.
- Junos OSPFv3 has a specific MTU-related quirk when operating over GRE.
- FRR-based test setups are useful for exposing real-world protocol compatibility problems.