Some Frequently Asked Questions, with brief Answers.

# 13 Some Frequently Asked Questions, with brief Answers.

Contents of this section

Following are some questions and answers that are commonly asked.

## 13.1 General questions:

I have only a dialin terminal access to a machine on the net, can I use this as a network connection ?

  Yes you can, take a look at TERM. TERM allows you you to run network connections over a normal terminal session. It requires some modifications to the network applications to work with it, but binaries and sources are available for the most common ones already. take a look at the TERM-HOWTO for lots more information.

I want to build my own standalone network, what addresses do I use ?

  RFC1597 has specifically reserved some IP addresses for private networks. You should use these as they prevent anything nasty happening if you accidentally get connected to the Internet. The addresses reserved are:

  > `

  >     10.0.0.0        -   10.255.255.255
  >     172.16.0.0      -   172.31.255.255
  >     192.168.0.0     -   192.168.255.255

  > `

  Note, reserved network addresses are of classes A, B and C, so you are not restricted in your network design or size. Since you won't be connecting to the Internet it doesn't matter if you use the same address as some other group or network, just so long as the addresses you use are unique within your network.

If sunacm.swan.ac.uk is down, how do I get the files specified ?

  `sunacm' is mirrored on:

  ftp.Uni-Mainz.DE

  > `

  >     /pub/Linux/packages/Net2Debugged

  > `

How do I know what version of kernel/net code I am running ?

  The network code and kernel now have synchronised version numbers, so try:

  `uname -a`

  or:

  `cat /proc/version`

## 13.2 Error messages:

I keep getting the error `eth0: transmit timed out'. What does this mean?

  This usually means that your Ethernet cable is unplugged, or that the setup parameters for your card (I/O address, IRQ, etc.) are not set correctly. Check the messages at boot time and make sure that your card is recognized with the correct Ethernet address. If it is, check that there is no conflict with any other hardware in your machine, eg you might have a soundblaster sharing the same IRQ or i/o control port.

I get errors `check Ethernet cable' when using the network.

  You probably have your Ethernet card configured incorrectly. Double check the settings in /usr/src/linux/drivers/net/CONFIG. If this checks out ok, you may in fact have a cabling problem, check the cables are plugged in securely.

## 13.3 Routing questions:

Why do I get the message `obselete route request' when I use the route command ?

  You are using a version of route that is older than your kernel. You should upgrade to a newer version of route. Refer to the "The network configuration tool suite" section of this document for information on where to obtain the tool set.

Why do I get a `network unreachable' message when I try and network?

  This message means that yours, or some other, machine doesn't know how to route to the host that you are attempting to ping or connect to. If it occurs for all hosts that you try, then it is probable that you don't have your default route set up properly, reread the `routing' section.

I can ping my server/gateway, but can't ping or connect to anyone remote.

  This is probably due to a routing problem. Reread the `routing' section in this document. If this looks ok, then make sure that the host you are attempting to connect to has a route to you. If you are a dialin user then this is a common cause of problems, ensure that your server is either running a routing program like gated or routed, or that it is `prox arping' for you, otherwise you will be able to get datagrams to the remote host, but it won't know how to return datagrams to you.

## 13.4 Using Linux with fileservers/NFS:

How do I use my existing Novell fileserver with my Linux machine ?

  If you have the Novell NFS Daemon code then it is easy, just NFS mount the Novell volume that you wish to use. If you don't, and you are really desperate to be able to do this, and you have a spare pc machine laying about, you are in luck. You can run a program called Stan's Own Server on the spare PC. First, configure the pc as a novell workstation with maps to the directories you want to nfs mount, then run SOS, and export those drive maps. SOS is available from spdcc.com:pub/sos/sossexe.zoo

Files get corrupted when running NFS over a network.

  Certain vendors (Sun primarily) shipped many machines running NFS without UDP checksums. Great on ethernet, suicide otherwise. UDP checksums can be enabled on most file servers. Linux has it enabled by default from pl13 onwards - but both ends need to have it enabled...

Why are my NFS files all read only ?

  The Linux NFS server defaults to read only. RTFM the `exports' and nfsd manual pages. With non Linux servers you may also need to alter /etc/exports

## 13.5 slip questions:

What do I do if I don't know my slip servers address ?

  dip doesn't really need to know the address of your slip server for slip to function. The remote option was added as a convenience so that dip could automate the ifconfig and route commands for you. If you don't know, and cannot find out the address of your slip server then Peter D. Junger `Junger@samsara.law.cwru.edu` has suggested that he simply used his own address wherever a dip script called for a remote address. This is a small kludge but it works ok, as the server's address never actually appears in the slip headers anyway.

`dip' only works for root. How do I make it work for others?

  dip needs to be suid root to perform some of the tasks necessary to do its job, so check that the file permissions of dip are `6750`. On some systems dip is actually a symbolic link to another file, such as dip.uri, if this is how yours is setup then make the change to that file instead. Something like ``chmod 6750 dip'` should work ok. Check also that dip is owned by root: ``chown root:dip dip'`.

With SLIP I can ping my server, and other hosts, but telnet or ftp don't work.

  This is most likely caused by a disagreement on the use of header compression between your server and your machine. Double check that both ends either are, or are not, using compression. They must match.

How can I hang up the phone line when I'm done using SLIP?

  If you use dip to dial out on the SLIP line, just `dip -k' should do the trick. If not, try to kill the dip process that is running. When dip dies it should hang up the call. To give it the best chance to clean up after itself, try killing the process in the following sequence: `kill <pid>', `kill -hup <pid>', and finally, if the dip process still refuses to die, try `kill -9 <pid>'. The same philosophy should be applied to all unix processes that you are attempting to kill.

I see a lot of overrun errors on my slip port, why ?

  The older network tools incorrectly report number of packets compressed as the number of packets overrun. This has been corrected, and shouldn't occur of you are running the new version kernel and tools. If it still is it probably indicates that your machine isn't keeping up with the rate of data incoming. If you are not using 16550AFN UARTs then you should upgrade to them. 16450, or 8250 generate an interrupt for every character they receive and are therefore very reliant on the processor to be able to find time to stop what it is doing an collect the character from them to ensure none get lost. The 16500AFN has a 16 character FIFO, and they only generate interrupts when the FIFO is nearly full, or when they have had character waiting, this means that less interrupts get generated for the same amount of data, and that less time is spent servicing your serial port. If you want to use multiple serial ports you should mandatorily upgrade to 16550AFN UARTs anyway.

Can I use two slip interfaces ?

  Yes. If you have, for example, three machines which you would like to interconnect, then you most certainly could use two slip interfaces on one machine and connect each of the other machines to it. Simply configure the second interface as you did the first. NOTE that the second interface will require a different IP address to the first. You may need to play with the routing a bit to get it to do what you want, but it should work.

I have a multiport i/o card, how do I use more than 4 slip ports ?

  The kernel slip comes with a default of a maximum of 4 slip devices configured, this is set in the `/usr/src/linux/drivers/net/slip.h` file. To increase it, say to `16`, change the `#define SL_NRUNIT` to `16`, in place of the `4` that will be there. You also need to edit `/usr/src/linux/drivers/net/Space.c` and add sections for `sl4`, `sl5` etc. You can copy the existing driver definition as a template to make it easier. You will need to recompile the kernel for the change to take effect.

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