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                    Linux DECnet Networking Layer Information

                   ===========================================

1) Other documentation....

   o Project Home Pages

       http://www.chygwyn.com/DECnet/                      - 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

malfunction.

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

want to.

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:

    decnet=1,2

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//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

parameters.

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:

    MACADDR=AA:00:04:00:03:04

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//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

effects).

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:

http://sourceforge.net/mail/?group_id=4993

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