> Try to formulate an good algorithm for it and you'll see. When do you want to Yeah, there isn't a perfect way to go about it. The informational RFC that suggests blackhole discovery doesn't even make useful suggestions about how it's properly done. > In practice everybody seems to just rewrite MSS options instead. Alright, here's my situation: I have a large network of mostly-Apache servers to millions of clients worldwide, mostly running Windows. I am finding that I have blackhole-related issues some of these clients. Microsoft has a workaround that works in at least SOME cases: on the last retransmit, unset DF and use an MTU of 576. Though it's a hack it *does* mean a fair number of those clients are able to reach me through broken networks, but I can't talk back -- I get a GET and sending the data back fails. Since there are potentially thousands of networks involved, I can't exactly just call every network administrator involved and suggest they stop blocking icmp or upgrade their broken routers. USing MSS clamping would be pretty suboptimal -- the problem isn't my direct uplink, it's some number of broken transit nets between me and some number of clients, and for all the rest of my clients I *want* to use pmtu discovery. Financially speaking, I can't give up on those users, because every one I don't talk to is money I don't make. I'm not saying that blackhole discovery should be on by default, or that it shouldn't be surrounded by flashing red neon signs warning the user it's a terrible hack, but it seems like there must be a lot of major networks running Linux servers that could use this feature. It looks like the only option I've got is to switch to Windows servers if I want to talk to these users ... or to implement it myself. That said, I'm digging 'round in the code trying to figure out how to do it -- if anybody has suggestions, I'd love to hear them. -- thanks, Will - : send the line "unsubscribe linux-net" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
