Tech the halls

[j4]

On my own in the house for the first time these hols, surrounded by glittering piles of shiny tech, I've finally found the motivation to try to set up my SonyEricsson P900 to talk to my computer. (I've only had the P900 for about 8 months, so this is something of a record for me in terms of getting round to configuring things.) First things first, install the software on the two CDs that came with the phone... that's the two PC CDs. Hmm.

Never mind, eh; Macs are clever, so I'll just use iSync to do its clever stuff... except that iSync can't see any devices within range, despite the fact that Bluetooth file sharing was eventually persuaded to see my phone once I told it that it was an 'other device' rather than a phone (though it still can't see any files on it).

What am I doing wrong?

The other tech task I'd planned to get done today was to transfer some files from a mac floppy disk to my laptop. Easy! ... Except that the mac with a floppy drive isn't on the network and doesn't have a USB port, and the PC (which also isn't on the network) which has a floppy drive and a USB port won't read this (rather ancient) vintage of mac disk. Maybe I'll get bored enough yet that I'll try to find a more recent mac/PC floppy disk, transfer the files from one disk to the other on the mac, then use the PC to read the newer disk... or maybe I'll wait till I get back to Cambridge, where I have an external USB floppy drive for the mac.

Meanwhile, while wireless network and BROADBAND are very much appreciated, it's irritating that the built-in firewall here seems to block anything useful (ssh, telnet, ftp). This means that I can only get to chiark (where all my mail is) via mindterm, which is okay except that due to some as yet undiagnosed terminal weirdness tab doesn't work. Which means I can't tab to the next new mail (in an inbox with 1772 mails in it, this is actually something of a problem) and I can't tab-complete anything. Annoying.

In other news: not only do I appear to have no network-fu, I seem to have lost all my elite gamer-fu. sion_a bought me the Sonic Mega Collection for Christmas, and I have been hedgehogging the telly to fuel my videogame addiction ever since. However I completely FAILED to finish Sonic 2 despite having 12 lives at the start of Death Egg Zone, and I can't even get past the Labyrinth Zone boss on original Sonic. And I can't unlock Sonic Spinball until I've finished one or more of the first three games! My left thumb is blistered, I'm seeing gold rings in front of my eyes, but the evil Doctor Robotnik remains unvanquished. I'll get you next time, Robotnik, just see if I don't...

Comments

[simont]

the built-in firewall here seems to block anything useful (ssh, telnet, ftp). This means that I can only get to chiark (where all my mail is) via mindterm

That's odd: MindTerm is an SSH client. If it works, then the firewall can't be blocking all SSH; so if other SSH clients don't work, there must be some other more subtle reason why.

My first thought was that perhaps chiark's MindTerm was configured to connect to ssh443.chiark.greenend.org.uk port 443, so as to appear like an HTTPS connection and fool firewalls, but (looking at the chiark MindTerm page) apparently not. On the other hand, it might be worth trying that with your normal SSH client...

[j4.livejournal.com]

MindTerm is an SSH client.

Oh, er, good point. *looks confused*

Your magic port 443 thing looked like it was going to work: it connected and asked me for a password ... but then it hung.

[j4.livejournal.com]

Further info, in case this helps a diagnosis*: my sister says that the outgoing connection is working fine, but the server that's being connected to is trying to send something back, & it's that that's not getting through. *handwave*

(Er, that's my handwave, not hers; she knows what she's talking about, but I don't, so I'm possibly misrepresenting the situation... sorry.)

* not that I'm expecting you to do remote network support! so feel free to ignore this...

[simont]

There is one thing that's been persistently springing to mind. I've never seen it happen myself, but every time someone on comp.security.ssh posts about mysterious problems with SSH connections, the local FAQ guru usually posts a link to http://www.snailbook.com/faq/mtu-mismatch.auto.html. Apparently the basic deal is that SSH tends to give rise to larger TCP packets than most other protocols and this can expose firewall bugs which you'd otherwise not have noticed.

OTOH, since it recommends changing the server configuration, this may not be optimally useful to you either, especially if your sister is correct in saying that the problem is with chiark sending stuff back...

[j4.livejournal.com]

Thanks for the link -- sounds complicated... to be honest I don't think I really understand what's happening where. I don't know if Lorna's correct but what she says fits the symptoms -- I get as far as the password prompt, type in a password and hit return, and that's when it hangs. So that suggests to me (not that I know anything! :-) that it's the return whatsits that's not getting through (unless for some reason the password isn't being sent properly, but then wouldn't that just give an error of some kind? ... I have no idea, as you can probably tell...).

On the other hand the possibility of reconfiguring the firewall here is about as unlikely as that of reconfiguring chiark, so I suspect it's a moot point. :-/

[imc.livejournal.com]

That reference gives a very plausible explanation (in fact one of my former colleagues wrote a broken ipchains script which drops fragmented packets and he still seems to be supplying systems with this on them).

There's a second common explanation for MTU-related network problems of this kind, which is that the firewall blocks incoming ICMP packets. What normally happens if you send too large a packet is that the objecting router sends back a ICMP packet saying fragmentation is required, and your machine responds by lowering its MTU for that route. If the firewall is blocking ICMP then this message doesn't get across and your machine carries on sending large packets, all of which end up in a black hole. This explanation fits the "chiark sending something back" scenario, except that as far as I can tell the route from cable.ntl.com (i.e., my machine) to chiark has an MTU of 1500 which is usually the maximum possible. (If it affected more than just chiark then you wouldn't be able to post long LiveJournal posts.)

However, if it is that, and your local firewall isn't dropping fragmented packets, then you can fix the problem by lowering your own MTU even if you can't change anything on the firewall.