| 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>