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Multi-VPN configuration
by Mark Rogers 04 Jun '12

04 Jun '12

I always get into a muddle when I try to set up VPN connections but I'm going to have another go.. What I have is lots of Linux "devices" (typically ARM boxes running Debian) which will be plugged into networks giving them Internet access. What I want to achieve is to have them auto-connect to a VPN, such that I am able to access all of them, but also that the end user can connect to their own devices but nobody elses. Ideally I'd also like other VPN capable devices, such as Draytek routers, to be able to join in the party. My starting point - which may well be wrong, is to assume that I want a server running OpenVPN somewhere on t' Internet. (Is that the right place to start?) I find the OpenVPN documentation to be very detailed but hard to narrow it down to any particular usage case unless it's a standard config (eg "road warrier"). What I don't want at my end is to *have* to connect separately to each VPN. Doing so optionally would be good (but would be possible in the same way an extra device could), but it could be I end up with dozens or hundreds of separate segregated VPNs. Furthermore, it's likely that I will want all of the VPNs to have access to certain facilities (eg databases, FTP) on other servers without having to make the other servers join multiple VPNs. -- Mark Rogers // More Solutions Ltd (Peterborough Office) // 0844 251 1450 Registered in England (0456 0902) 21 Drakes Mews, Milton Keynes, MK8 0ER

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How to print stupid Royal Mail price list?
by Chris Green 01 Jun '12

01 Jun '12

The Royal Mail used to provide a neat PDF file which fitted A4 to show their postage prices. The latest version though is a 'booklet' so I can't see any way to actually print it on an A4 printer. This is the link to the PDF:- http://c435158.r58.cf3.rackcdn.com/Royal_Mail_Our_Prices.pdf Can anyone tell me how to split it up into printable pages? I've tried ImageMagick's convert but that didn't default to what I wanted, maybe I need some more options to tell it what to do. -- Chris Green

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Programming question - different approaches to classic command parsing
by Chris Green 29 May '12

29 May '12

Well my Nanode project is progressing (it's the one that has the rather idiosyncratic ethernet handling). The next question is whether to rejig the basic command handling. The Nanode software I'm maintaining/improving is basically very simple, after initialisation it waits for an ethernet UDP packet with a command code and data in it, then it acts on the command and returns (via UDP again) some sort of response. There are currently 34 commands, this will expand somewhat but is unlikely to ever be more than 100 or so. The existing code simply has a switch/case block switching on the command code with the cases handling each command. It's a bit long but is manageable. I'm wondering whether to stay with the existing structure or to go to some sort of table driven approach with an array of something like:- // // // Command table entry structure // struct command { uint32_t cmd; // the command code int (* fnc) (int addr); // the address of the function to call char * str; // the associated LCD string }; (obviously the function parameters may extend/change) A linear search of an array of these won't waste much time, speed isn't of great consequence anyway. Then each command will be a function, tidier and more modular, but will it actually win me anything (or lose anything)? In particular will it use more space, in code or RAM? In code there will be, say, 50 function calls plus a table instead of a switch statement with 50 case: blocks. In RAM there will be lots of smaller functions using a small amount of stack space instead of one big one with lots of local variables. This is using the gcc-avr compiler by the way. My gut feeling is that it probably won't make a big difference either in code space use or in RAM use but it will probably use a little bit more of both. The question then is whether the significant amount of rewriting is worth it for the more elegant (and hence easy to maintain) code. If there's another approach to managing this sort of command driven interface then I'd be interested in hearing about it. -- Chris Green

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Re: [ALUG] Ethernet programming question
by Phil Ashby 28 May '12

28 May '12

Chris Green <cl(a)isbd.net> wrote: > I'm doing some programming of a Nanode board (not far removed from > Arduino) which has an ethernet interface based on the ENC28J60. > ... > However the loop that waits for ethernet packets and deals with them > seems a bit odd to me, in psuedo-code it's something like:- > > while (not reset) > { > get a packet from ethernet > > handle DHCP message > > handle message requesting local display on LCD > > handle ARP request > > handle DNS request > > handle NTP request > > if (still something left) > { > if (ping) > { > respond to ping > } > if (UDP message for us) > { > handle our message > } > } > } > > > What I'm not clear about is whether one packet can only be one of the > above things. Hence, if a DHCP request of some sort has been received > and handled can the *same* packet contain other requests? If not then > why is the code going through all the other calls? Hi Chris - you are correct in assuming that one packet can only be one thing, since a combination of packet type fields (Ethernet frame type, IP frame type, TCP/UDP port number) determine this. > OK, it makes for simpler looking code, no conditionals and/or > switch/case but it somehow seems wrong (and a bit inefficient as each > handle function gets called even if the packet has already been > handled). Just been and looked at the code in github for the Nanode Ethershield and all I can say is yuk! https://github.com/Nanode/EtherShield/blob/master/ip_arp_udp_tcp.c I quote: "The TCP implementation uses some size optimisations which are valid only if all data can be sent in one single packet. This is however not a big limitation for a microcontroller as you will anyhow use small web-pages." Hmmn. I found the code confusing, badly structured and incomplete (eg: it doesn't work if IP options are sent and there is nothing like the full TCP state machine with various timers, backoff controls and such, only a happy path). Of course I may have been looking at different code - got a URL? Phil. PS: http://code.google.com/p/avr-uip/ looks rather better!

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Ethernet programming question
by Chris Green 28 May '12

28 May '12

I'm doing some programming of a Nanode board (not far removed from Arduino) which has an ethernet interface based on the ENC28J60. I'm only modifying the existing software rather than building from scratch but would like to tidy things as much as possible. The ethernet initialisation etc. is standard library code so is cast in stone as it were but I'm puzzling over the higher level ethernet message handling stuff a bit. The system basically handles incoming requests sent over the ethernet interface and replies with instrument data, this part of the code is pretty straightforward. However the loop that waits for ethernet packets and deals with them seems a bit odd to me, in psuedo-code it's something like:- while (not reset) { get a packet from ethernet handle DHCP message handle message requesting local display on LCD handle ARP request handle DNS request handle NTP request if (still something left) { if (ping) { respond to ping } if (UDP message for us) { handle our message } } } What I'm not clear about is whether one packet can only be one of the above things. Hence, if a DHCP request of some sort has been received and handled can the *same* packet contain other requests? If not then why is the code going through all the other calls? OK, it makes for simpler looking code, no conditionals and/or switch/case but it somehow seems wrong (and a bit inefficient as each handle function gets called even if the packet has already been handled). -- Chris Green

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Ripping MP3s
by Chris Walker 23 May '12

23 May '12

I have a Creative Zen MP3 player which I use in my car. I want to tidy up a load of CDs which have accumulated over the years before they go to the bin. They're freebies from newspapers and so aren't worth anything and have the usual half dozen decent tracks followed a dozen rubbish tracks. But I'm stuck trying to rip them to MP3. I've tried k3b but that doesn't offer MP3 as an output option. I've also installed soundkonverter (rather than soundconverter as I'm using kde for a desktop) but despite saying that it can use FFmpeg as a plugin, there is still no MP3 option. Am I doing something wrong? The system is Mandriva 2011 64 bit.

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[very off topic] drill press
by David Reynolds 22 May '12

22 May '12

Hi guys, Does anyone in the Norwich-ish area happen to have (or have access to) a drill press I could use? I am building a guitar from a kit and I need to drill 4 holes with said drill press. Can anyone help? -- David Reynolds david(a)reynoldsfamily.org.uk

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Tonight's Ipswich ALUG meet
by samwise 22 May '12

22 May '12

Well, looks like there's at least three of us out tonight. I thought I'd suggest that after giving it half an hour or so for stragglers, that we might want to try moving back to our old venue The Milestone (now The Mulberry Bush) tonight. It's been reinvented and is a proper real ale pub now, and may well be an improvement on McGinty's ... plus the poker night that turfed us out has long since gone. :) Not sure of the wi-fi situation but it can't be worse than McGinty's! So anyone who wants to come out to play tonight who might be late, come find us at The Mulberry Bush! Peter.

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Can't get 1000Mb/s on ethernet port which should be capable
by Chris Green 19 May '12

19 May '12

I am backing up some data from a Dell Vostro V13 laptop which is currently running xubuntu 10.04 (the reason for the backup is that I'm aiming to install 12.04). The ethernet port is running at only 100Mb/s whereas it's supposed to be a gigabit capable port. Running ethtool shows:- Settings for eth0: Supported ports: [ TP MII ] Supported link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Half 1000baseT/Full Supports auto-negotiation: Yes Advertised link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Half 1000baseT/Full Advertised pause frame use: No Advertised auto-negotiation: Yes Link partner advertised link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full Link partner advertised pause frame use: No Link partner advertised auto-negotiation: Yes Speed: 100Mb/s Duplex: Full Port: MII PHYAD: 0 Transceiver: internal Auto-negotiation: on Supports Wake-on: pumbg Wake-on: g Current message level: 0x00000033 (51) Link detected: yes Running ethtool on my desktop machine connected to the *same* switch shows:- Settings for eth0: Supported ports: [ TP MII ] Supported link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Half 1000baseT/Full Supports auto-negotiation: Yes Advertised link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Half 1000baseT/Full Advertised pause frame use: Symmetric Receive-only Advertised auto-negotiation: Yes Link partner advertised link modes: 10baseT/Half 10baseT/Full 100baseT/Half 100baseT/Full 1000baseT/Full Link partner advertised pause frame use: Symmetric Receive-only Link partner advertised auto-negotiation: Yes Speed: 1000Mb/s Duplex: Full Port: MII PHYAD: 0 Transceiver: internal Auto-negotiation: on Supports Wake-on: pumbg Wake-on: g Current message level: 0x00000033 (51) drv probe ifdown ifup Link detected: yes So why are the two machines seeing different "Link partner" settings? I tried Googling for "Link partner" but couldn't find anywhere that actually tells me what they mean, it *sounds* like it's what the 'other end' is advertising but from what I see above maybe it isn't. By the way I have tried changing the ethernet cable, no change at all. Can anyone elucidate things? -- Chris Green

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Back issues of Linux Format (97 Oct 07 - 127 Jan 10)
by Andrew Williams 19 May '12

19 May '12

Hello all. I'm having a clear out of some of my older Linux Format issues. Would anyone like them before I consign them to the recyling bin? Most DVDs also included. Cheers, Andrew.

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