компьютерное (компьютерное)

[avva]

Час вчера промудохался, пытаясь заставить Windows XP и Windows 7 в домашней сетке видеть друг друга. Они находили друг друга по IP, но имена друг друга отказывались видеть. После прочтений бесчисленных ФАКов и проверок всего, что связанно с магическими словами netbios и WINS, я уже почти было сдался, но в последний момент проверил - я бы рад сказать, что сам догадался, но на самом деле мелькнуло в очередном ФАКе - какой у них сконфигурирован subnet mask; оказалось, что у XP стоял почему-то 255.0.0.0. Это ничему другому не мешало, кроме вот этого.

Ненавижу компьютеры.

Comments

[gaal.livejournal.com]

The broadcast address is implied by the subnet mask on Windows, IIRC.

[avva.livejournal.com]

I thought it was an ipv4 thing, not a specifically Windows thing?

Anyway, the point is, nothing pointed me towards checking that subnet masks are the same on both boxes, not the official microsoft FAQs and KB articles, nor the Win7 troubleshooting thingie, nor most of the informal FAQs I skimmed. I probably could have, and should have, guessed to check this earlier, but I was stuck in the whole netbios/WINS resolution foxhole - there's _lots_ of things there that can go wrong and have the same visible effect, so I was checking those things one by one and wondering what I'd missed.

[gaal.livejournal.com]

Not precisely: although generally speaking the broadcast address is the last address in the block, old stacks used to use the first (and I suppose it might actually be legal, though bizarre, to use another arbitrary address inside the range). What my comment was referring to was that on Unix with the ifconfig command, you sometimes (i.e., on older systems) have to explicitly state the broadcast address, which feels useless but is actually another opportunity to notice the misconfiguration.

I'm not a big fan of dotted-quad notation for subnet masks, because mistakes like these are easy to make. 255.0.0.0 vs. 255.255.255.0 is pretty forest-for-the-trees. 192.168.1/8 and 10/24 on the other hand immediately look fishy once you understand what they mean. This is just a notation thing, but and example where notation is significant.

Windows networking relies a lot on broadcasting, both for discovery—which was where your network setup failed you—and I believe for actual communication in some conditions. This is why it's easy to set up in the trivial cases, and a pain in the ass elsewhere. There are several "modes" like b, h, and so on that determine what discovery method a host will attempt and IIRC ipconfig /all shows the active one. It's been several happy years since I touched this stuff, so I don't remember how to actually change the mode.

Whoever mentioned a sniffer is technically right, you would have been able to see two hosts broadcasting to different addresses with discovery calls and neither receiving an answer.