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