233 lines
10 KiB
Plaintext
233 lines
10 KiB
Plaintext
Linux DECnet Networking Layer Information
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===========================================
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1) Other documentation....
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o Project Home Pages
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http://www.chygwyn.com/ - Kernel info
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http://linux-decnet.sourceforge.net/ - Userland tools
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http://www.sourceforge.net/projects/linux-decnet/ - Status page
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2) Configuring the kernel
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Be sure to turn on the following options:
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CONFIG_DECNET (obviously)
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CONFIG_PROC_FS (to see what's going on)
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CONFIG_SYSCTL (for easy configuration)
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if you want to try out router support (not properly debugged yet)
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you'll need the following options as well...
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CONFIG_DECNET_ROUTER (to be able to add/delete routes)
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CONFIG_NETFILTER (will be required for the DECnet routing daemon)
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CONFIG_DECNET_ROUTE_FWMARK is optional
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Don't turn on SIOCGIFCONF support for DECnet unless you are really sure
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that you need it, in general you won't and it can cause ifconfig to
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malfunction.
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Run time configuration has changed slightly from the 2.4 system. If you
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want to configure an endnode, then the simplified procedure is as follows:
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o Set the MAC address on your ethernet card before starting _any_ other
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network protocols.
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As soon as your network card is brought into the UP state, DECnet should
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start working. If you need something more complicated or are unsure how
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to set the MAC address, see the next section. Also all configurations which
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worked with 2.4 will work under 2.5 with no change.
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3) Command line options
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You can set a DECnet address on the kernel command line for compatibility
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with the 2.4 configuration procedure, but in general it's not needed any more.
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If you do st a DECnet address on the command line, it has only one purpose
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which is that its added to the addresses on the loopback device.
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With 2.4 kernels, DECnet would only recognise addresses as local if they
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were added to the loopback device. In 2.5, any local interface address
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can be used to loop back to the local machine. Of course this does not
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prevent you adding further addresses to the loopback device if you
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want to.
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N.B. Since the address list of an interface determines the addresses for
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which "hello" messages are sent, if you don't set an address on the loopback
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interface then you won't see any entries in /proc/net/neigh for the local
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host until such time as you start a connection. This doesn't affect the
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operation of the local communications in any other way though.
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The kernel command line takes options looking like the following:
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decnet.addr=1,2
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the two numbers are the node address 1,2 = 1.2 For 2.2.xx kernels
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and early 2.3.xx kernels, you must use a comma when specifying the
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DECnet address like this. For more recent 2.3.xx kernels, you may
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use almost any character except space, although a `.` would be the most
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obvious choice :-)
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There used to be a third number specifying the node type. This option
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has gone away in favour of a per interface node type. This is now set
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using /proc/sys/net/decnet/conf/<dev>/forwarding. This file can be
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set with a single digit, 0=EndNode, 1=L1 Router and 2=L2 Router.
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There are also equivalent options for modules. The node address can
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also be set through the /proc/sys/net/decnet/ files, as can other system
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parameters.
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Currently the only supported devices are ethernet and ip_gre. The
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ethernet address of your ethernet card has to be set according to the DECnet
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address of the node in order for it to be autoconfigured (and then appear in
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/proc/net/decnet_dev). There is a utility available at the above
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FTP sites called dn2ethaddr which can compute the correct ethernet
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address to use. The address can be set by ifconfig either before or
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at the time the device is brought up. If you are using RedHat you can
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add the line:
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MACADDR=AA:00:04:00:03:04
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or something similar, to /etc/sysconfig/network-scripts/ifcfg-eth0 or
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wherever your network card's configuration lives. Setting the MAC address
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of your ethernet card to an address starting with "hi-ord" will cause a
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DECnet address which matches to be added to the interface (which you can
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verify with iproute2).
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The default device for routing can be set through the /proc filesystem
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by setting /proc/sys/net/decnet/default_device to the
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device you want DECnet to route packets out of when no specific route
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is available. Usually this will be eth0, for example:
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echo -n "eth0" >/proc/sys/net/decnet/default_device
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If you don't set the default device, then it will default to the first
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ethernet card which has been autoconfigured as described above. You can
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confirm that by looking in the default_device file of course.
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There is a list of what the other files under /proc/sys/net/decnet/ do
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on the kernel patch web site (shown above).
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4) Run time kernel configuration
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This is either done through the sysctl/proc interface (see the kernel web
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pages for details on what the various options do) or through the iproute2
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package in the same way as IPv4/6 configuration is performed.
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Documentation for iproute2 is included with the package, although there is
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as yet no specific section on DECnet, most of the features apply to both
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IP and DECnet, albeit with DECnet addresses instead of IP addresses and
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a reduced functionality.
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If you want to configure a DECnet router you'll need the iproute2 package
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since its the _only_ way to add and delete routes currently. Eventually
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there will be a routing daemon to send and receive routing messages for
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each interface and update the kernel routing tables accordingly. The
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routing daemon will use netfilter to listen to routing packets, and
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rtnetlink to update the kernels routing tables.
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The DECnet raw socket layer has been removed since it was there purely
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for use by the routing daemon which will now use netfilter (a much cleaner
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and more generic solution) instead.
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5) How can I tell if its working ?
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Here is a quick guide of what to look for in order to know if your DECnet
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kernel subsystem is working.
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- Is the node address set (see /proc/sys/net/decnet/node_address)
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- Is the node of the correct type
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(see /proc/sys/net/decnet/conf/<dev>/forwarding)
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- Is the Ethernet MAC address of each Ethernet card set to match
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the DECnet address. If in doubt use the dn2ethaddr utility available
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at the ftp archive.
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- If the previous two steps are satisfied, and the Ethernet card is up,
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you should find that it is listed in /proc/net/decnet_dev and also
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that it appears as a directory in /proc/sys/net/decnet/conf/. The
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loopback device (lo) should also appear and is required to communicate
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within a node.
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- If you have any DECnet routers on your network, they should appear
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in /proc/net/decnet_neigh, otherwise this file will only contain the
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entry for the node itself (if it doesn't check to see if lo is up).
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- If you want to send to any node which is not listed in the
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/proc/net/decnet_neigh file, you'll need to set the default device
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to point to an Ethernet card with connection to a router. This is
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again done with the /proc/sys/net/decnet/default_device file.
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- Try starting a simple server and client, like the dnping/dnmirror
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over the loopback interface. With luck they should communicate.
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For this step and those after, you'll need the DECnet library
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which can be obtained from the above ftp sites as well as the
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actual utilities themselves.
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- If this seems to work, then try talking to a node on your local
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network, and see if you can obtain the same results.
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- At this point you are on your own... :-)
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6) How to send a bug report
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If you've found a bug and want to report it, then there are several things
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you can do to help me work out exactly what it is that is wrong. Useful
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information (_most_ of which _is_ _essential_) includes:
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- What kernel version are you running ?
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- What version of the patch are you running ?
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- How far though the above set of tests can you get ?
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- What is in the /proc/decnet* files and /proc/sys/net/decnet/* files ?
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- Which services are you running ?
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- Which client caused the problem ?
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- How much data was being transferred ?
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- Was the network congested ?
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- How can the problem be reproduced ?
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- Can you use tcpdump to get a trace ? (N.B. Most (all?) versions of
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tcpdump don't understand how to dump DECnet properly, so including
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the hex listing of the packet contents is _essential_, usually the -x flag.
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You may also need to increase the length grabbed with the -s flag. The
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-e flag also provides very useful information (ethernet MAC addresses))
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7) MAC FAQ
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A quick FAQ on ethernet MAC addresses to explain how Linux and DECnet
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interact and how to get the best performance from your hardware.
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Ethernet cards are designed to normally only pass received network frames
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to a host computer when they are addressed to it, or to the broadcast address.
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Linux has an interface which allows the setting of extra addresses for
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an ethernet card to listen to. If the ethernet card supports it, the
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filtering operation will be done in hardware, if not the extra unwanted packets
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received will be discarded by the host computer. In the latter case,
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significant processor time and bus bandwidth can be used up on a busy
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network (see the NAPI documentation for a longer explanation of these
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effects).
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DECnet makes use of this interface to allow running DECnet on an ethernet
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card which has already been configured using TCP/IP (presumably using the
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built in MAC address of the card, as usual) and/or to allow multiple DECnet
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addresses on each physical interface. If you do this, be aware that if your
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ethernet card doesn't support perfect hashing in its MAC address filter
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then your computer will be doing more work than required. Some cards
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will simply set themselves into promiscuous mode in order to receive
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packets from the DECnet specified addresses. So if you have one of these
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cards its better to set the MAC address of the card as described above
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to gain the best efficiency. Better still is to use a card which supports
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NAPI as well.
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8) Mailing list
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If you are keen to get involved in development, or want to ask questions
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about configuration, or even just report bugs, then there is a mailing
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list that you can join, details are at:
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http://sourceforge.net/mail/?group_id=4993
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9) Legal Info
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The Linux DECnet project team have placed their code under the GPL. The
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software is provided "as is" and without warranty express or implied.
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DECnet is a trademark of Compaq. This software is not a product of
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Compaq. We acknowledge the help of people at Compaq in providing extra
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documentation above and beyond what was previously publicly available.
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Steve Whitehouse <SteveW@ACM.org>
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