Let me guess: Sun talking to Cisco, around late 1990s to early 2000s? A known bug, known to both vendors, neither would fix it, Solaris admins would just have to know about it, usually via having been bitten by it? Yeah.
I had to solve this one with a small hub or switch between the Sun and Cisco boxes, so it sounded very familiar. Possibly 10 vs 100 was harder than we thought.