1                    Linux DECnet Networking Layer Information
   2                   ===========================================
   41) Other documentation....
   6   o Project Home Pages
   7                      - Kernel info
   8                - Userland tools
   9   - Status page
  112) Configuring the kernel
  13Be sure to turn on the following options:
  15    CONFIG_DECNET (obviously)
  16    CONFIG_PROC_FS (to see what's going on)
  17    CONFIG_SYSCTL (for easy configuration)
  19if you want to try out router support (not properly debugged yet)
  20you'll need the following options as well...
  22    CONFIG_DECNET_ROUTER (to be able to add/delete routes)
  23    CONFIG_NETFILTER (will be required for the DECnet routing daemon)
  25    CONFIG_DECNET_ROUTE_FWMARK is optional
  27Don't turn on SIOCGIFCONF support for DECnet unless you are really sure
  28that you need it, in general you won't and it can cause ifconfig to
  31Run time configuration has changed slightly from the 2.4 system. If you
  32want to configure an endnode, then the simplified procedure is as follows:
  34 o Set the MAC address on your ethernet card before starting _any_ other
  35   network protocols.
  37As soon as your network card is brought into the UP state, DECnet should
  38start working. If you need something more complicated or are unsure how
  39to set the MAC address, see the next section. Also all configurations which
  40worked with 2.4 will work under 2.5 with no change.
  423) Command line options
  44You can set a DECnet address on the kernel command line for compatibility
  45with the 2.4 configuration procedure, but in general it's not needed any more.
  46If you do st a DECnet address on the command line, it has only one purpose
  47which is that its added to the addresses on the loopback device.
  49With 2.4 kernels, DECnet would only recognise addresses as local if they
  50were added to the loopback device. In 2.5, any local interface address
  51can be used to loop back to the local machine. Of course this does not
  52prevent you adding further addresses to the loopback device if you
  53want to.
  55N.B. Since the address list of an interface determines the addresses for
  56which "hello" messages are sent, if you don't set an address on the loopback
  57interface then you won't see any entries in /proc/net/neigh for the local
  58host until such time as you start a connection. This doesn't affect the
  59operation of the local communications in any other way though.
  61The kernel command line takes options looking like the following:
  63    decnet.addr=1,2
  65the two numbers are the node address 1,2 = 1.2 For 2.2.xx kernels
  66and early 2.3.xx kernels, you must use a comma when specifying the
  67DECnet address like this. For more recent 2.3.xx kernels, you may
  68use almost any character except space, although a `.` would be the most
  69obvious choice :-)
  71There used to be a third number specifying the node type. This option
  72has gone away in favour of a per interface node type. This is now set
  73using /proc/sys/net/decnet/conf/<dev>/forwarding. This file can be
  74set with a single digit, 0=EndNode, 1=L1 Router and  2=L2 Router.
  76There are also equivalent options for modules. The node address can
  77also be set through the /proc/sys/net/decnet/ files, as can other system
  80Currently the only supported devices are ethernet and ip_gre. The
  81ethernet address of your ethernet card has to be set according to the DECnet
  82address of the node in order for it to be autoconfigured (and then appear in
  83/proc/net/decnet_dev). There is a utility available at the above
  84FTP sites called dn2ethaddr which can compute the correct ethernet
  85address to use. The address can be set by ifconfig either before or
  86at the time the device is brought up. If you are using RedHat you can
  87add the line:
  89    MACADDR=AA:00:04:00:03:04
  91or something similar, to /etc/sysconfig/network-scripts/ifcfg-eth0 or
  92wherever your network card's configuration lives. Setting the MAC address
  93of your ethernet card to an address starting with "hi-ord" will cause a
  94DECnet address which matches to be added to the interface (which you can
  95verify with iproute2).
  97The default device for routing can be set through the /proc filesystem
  98by setting /proc/sys/net/decnet/default_device to the
  99device you want DECnet to route packets out of when no specific route
 100is available. Usually this will be eth0, for example:
 102    echo -n "eth0" >/proc/sys/net/decnet/default_device
 104If you don't set the default device, then it will default to the first
 105ethernet card which has been autoconfigured as described above. You can
 106confirm that by looking in the default_device file of course.
 108There is a list of what the other files under /proc/sys/net/decnet/ do
 109on the kernel patch web site (shown above).
 1114) Run time kernel configuration
 113This is either done through the sysctl/proc interface (see the kernel web
 114pages for details on what the various options do) or through the iproute2
 115package in the same way as IPv4/6 configuration is performed.
 117Documentation for iproute2 is included with the package, although there is
 118as yet no specific section on DECnet, most of the features apply to both
 119IP and DECnet, albeit with DECnet addresses instead of IP addresses and
 120a reduced functionality.
 122If you want to configure a DECnet router you'll need the iproute2 package
 123since its the _only_ way to add and delete routes currently. Eventually
 124there will be a routing daemon to send and receive routing messages for
 125each interface and update the kernel routing tables accordingly. The
 126routing daemon will use netfilter to listen to routing packets, and
 127rtnetlink to update the kernels routing tables. 
 129The DECnet raw socket layer has been removed since it was there purely
 130for use by the routing daemon which will now use netfilter (a much cleaner
 131and more generic solution) instead.
 1335) How can I tell if its working ?
 135Here is a quick guide of what to look for in order to know if your DECnet
 136kernel subsystem is working.
 138   - Is the node address set (see /proc/sys/net/decnet/node_address)
 139   - Is the node of the correct type 
 140                             (see /proc/sys/net/decnet/conf/<dev>/forwarding)
 141   - Is the Ethernet MAC address of each Ethernet card set to match
 142     the DECnet address. If in doubt use the dn2ethaddr utility available
 143     at the ftp archive.
 144   - If the previous two steps are satisfied, and the Ethernet card is up,
 145     you should find that it is listed in /proc/net/decnet_dev and also
 146     that it appears as a directory in /proc/sys/net/decnet/conf/. The
 147     loopback device (lo) should also appear and is required to communicate
 148     within a node.
 149   - If you have any DECnet routers on your network, they should appear
 150     in /proc/net/decnet_neigh, otherwise this file will only contain the
 151     entry for the node itself (if it doesn't check to see if lo is up).
 152   - If you want to send to any node which is not listed in the
 153     /proc/net/decnet_neigh file, you'll need to set the default device
 154     to point to an Ethernet card with connection to a router. This is
 155     again done with the /proc/sys/net/decnet/default_device file.
 156   - Try starting a simple server and client, like the dnping/dnmirror
 157     over the loopback interface. With luck they should communicate.
 158     For this step and those after, you'll need the DECnet library
 159     which can be obtained from the above ftp sites as well as the
 160     actual utilities themselves.
 161   - If this seems to work, then try talking to a node on your local
 162     network, and see if you can obtain the same results.
 163   - At this point you are on your own... :-)
 1656) How to send a bug report
 167If you've found a bug and want to report it, then there are several things
 168you can do to help me work out exactly what it is that is wrong. Useful
 169information (_most_ of which _is_ _essential_) includes:
 171 - What kernel version are you running ?
 172 - What version of the patch are you running ?
 173 - How far though the above set of tests can you get ?
 174 - What is in the /proc/decnet* files and /proc/sys/net/decnet/* files ?
 175 - Which services are you running ?
 176 - Which client caused the problem ?
 177 - How much data was being transferred ?
 178 - Was the network congested ?
 179 - How can the problem be reproduced ?
 180 - Can you use tcpdump to get a trace ? (N.B. Most (all?) versions of 
 181   tcpdump don't understand how to dump DECnet properly, so including
 182   the hex listing of the packet contents is _essential_, usually the -x flag.
 183   You may also need to increase the length grabbed with the -s flag. The
 184   -e flag also provides very useful information (ethernet MAC addresses))
 1867) MAC FAQ
 188A quick FAQ on ethernet MAC addresses to explain how Linux and DECnet
 189interact and how to get the best performance from your hardware. 
 191Ethernet cards are designed to normally only pass received network frames 
 192to a host computer when they are addressed to it, or to the broadcast address.
 194Linux has an interface which allows the setting of extra addresses for
 195an ethernet card to listen to. If the ethernet card supports it, the
 196filtering operation will be done in hardware, if not the extra unwanted packets
 197received will be discarded by the host computer. In the latter case,
 198significant processor time and bus bandwidth can be used up on a busy
 199network (see the NAPI documentation for a longer explanation of these
 202DECnet makes use of this interface to allow running DECnet on an ethernet 
 203card which has already been configured using TCP/IP (presumably using the 
 204built in MAC address of the card, as usual) and/or to allow multiple DECnet
 205addresses on each physical interface. If you do this, be aware that if your
 206ethernet card doesn't support perfect hashing in its MAC address filter
 207then your computer will be doing more work than required. Some cards
 208will simply set themselves into promiscuous mode in order to receive
 209packets from the DECnet specified addresses. So if you have one of these
 210cards its better to set the MAC address of the card as described above
 211to gain the best efficiency. Better still is to use a card which supports
 212NAPI as well.
 2158) Mailing list
 217If you are keen to get involved in development, or want to ask questions
 218about configuration, or even just report bugs, then there is a mailing
 219list that you can join, details are at:
 2239) Legal Info
 225The Linux DECnet project team have placed their code under the GPL. The
 226software is provided "as is" and without warranty express or implied.
 227DECnet is a trademark of Compaq. This software is not a product of
 228Compaq. We acknowledge the help of people at Compaq in providing extra
 229documentation above and beyond what was previously publicly available.
 231Steve Whitehouse <>
 233 kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.