9.1.1. Audience

This networking section of this guide explains various aspects of networking and is intended to help people with little knowledge about networks to get started. It is devided into three sections. We start by giving a general overview of how networking works and introduce the basic concepts. Then we go into details for setting up various types of networking in the second section, and the third section covers any "advanced" topics that go beyond the scope of basic operation as introduced in the first two sections.

The reader is assumed to know about basic system administration tasks: how to become root, edit files, change permissions, stop processes, etc. See [AeleenFrisch] for further information on this topic. Besides that, you should know how to handle the utilities we're going to set up here, i. e. you should know how to use telnet, FTP, ... I will not explain the basic features of those utilities, please refer to the appropriate man-pages, the references listed or of course the other parts of this document instead.

This Introduction to TCP/IP Networking was written with the intention in mind to give starters a basic knowledge. If you really want to know what's it all about, read [CraigHunt]. This book does not only cover the basics, but goes on and explains all the concepts, services and how to set them up in detail. It's great, I love it! :-)

9.1.2. Supported Networking Protocols

There are several protocol suites supported by NetBSD, most of which were inherited from NetBSD's predecessor, 4.4BSD, and subsequently enhanced and improved. The first and most important one today is DARPA's Transmission Control Protocoll/Internet Protocoll (TCP/IP). Other protocol suites available in NetBSD include the Xerox Network System (XNS) which was only implemented at UCB to connect isolated machines to the net, Apple's AppleTalk protocol suite and the ISO protocol suite, CCITT X.25 and ARGO TP. They are only used in some special applications these days.

Today, TCP/IP is the most widespread protocol of the ones mentioned above. It is implemented on almost every hardware and operating system, and it is also the most-used protocol in heterogenous environments. So, if you just want to connect your computer running NetBSD to some other machine at home, or you want to integrate it into your company's or university's network, TCP/IP is the right choice.

IPv6 (TCP/IP protocol issue 6, current version IPv4) is still under development, and the KAME project's IPv6 code was merged into NetBSD and shipped starting with the NetBSD 1.5 release.

There are other protocol suites such as DECNET, Novell's IPX/SPX or Microsoft's NetBIOS, but these are not currently supported by NetBSD. These two protocols differ from the protocols mentioned above in that they are proprietary, in contrast to the others, which are well-defined in several RFCs and other open standards.

9.1.3. Supported Media

TCP/IP can be used on a wide range of media. Among the ones supported by NetBSD are Ethernet (10/100/1000MBd), Arcnet, serial line, ATM, FDDI, Fiber Channel, USB, HIPPI, FireWire (IEEE 1394), Token Ring, serial lines and others.

9.1.4. TCP/IP Address Format

TCP/IP uses 4-byte (32-bit) addresses in the current implementations (IPv4), also called IP-numbers (Internet-Protocol numbers), to address hosts.

TCP/IP allows any two machines to communicate directly. To permit this all hosts on a given network must have a unique IP address. To assure this, IP addresses are administrated by one central organisation, the InterNIC. They give certain ranges of addresses (network-addresses) directly to sites which want to participate in the internet or to internet-providers, which give the addresses to their customers.

If your university or company is connected to the Internet, it has (at least) one such network-address for it's own use, usually not assigned by the InterNIC directly, but rather through an Internet Service Provider (ISP).

If you just want to run your private network at home, see below on how to "build" your own IP addresses. However, if you want to connect your machine to the (real :-) Internet, you should get an IP addresses from your local network-administrator or -provider.

IP addresses are usually written in "dotted quad"-notation - the four bytes are written down in decimal (most significant byte first), separated by dots. For example, 132.199.15.99 would be a valid address. Another way to write down IP-addresses would be as one 32-bit hex-word, e.g. 0x84c70f63. This is not as convenient as the dotted-quad, but quite useful at times, too. (See below!)

Being assigned a network means nothing else but setting some of the above-mentioned 32 address-bits to certain values. These bits that are used for identifying the network are called network-bits. The remaining bits can be used to address hosts on that network, therefore they are called host-bits.

In the above example, the network-address is 132.199.0.0 (host-bits are set to 0 in network-addresses), the host's address is 15.99 on that network.

How do you know that the host's address is 16 bit wide? Well, this is assigned by the provider from which you get your network-addresses. In the classless inter-domain routing (CIDR) used today, host fields are usually between as little as 2 to 16 bits wide, and the number of network-bits is written after the network address, seperated by a "/", e.g. 132.199.0.0/16 tells that the network in question has 16 network-bits. When talking about the "size" of a network, it's usual to only talk about it as "/16", "/24", etc.

Before CIDR was used, there used to be four classes of networks. Each one starts with a certain bit-pattern identifying it. Here are the four classes:

• Class A starts with "0" as most significant bit. The next seven bits of a class A address identify the network, the remaining 24 bit can be used to address hosts. So, within one class A network there can be 2²⁴ hosts. It's not very likely that you (or your university, or company, or whatever) will get a whole class A address.

  The CIDR notation for a class A network with it's eight network bits is an "/8".

• Class B starts with "10" as most significant bits. The next 14 bits are used for the networks address, the remaining 16 bits can be used to address more than 65000 hosts. Class B addresses are very rarely given out today, they used to be common for companies and universities before IPv4 address space went scarce.

  The CIDR notation for an class B network with it's 16 network bits is an "/16".

  Returning to our above example, you can see that 132.199.15.99 (or 0x84c70f63, which is more appropriate here!) is on a class B network, as 0x84... = 1000... (base 2).

  Therefore, the address 132.199.15.99 can be split into an network-address of 132.199.0.0 and an host-address of 15.99.

• Class C is identified by the MSBs being "110", allowing only 256 (actually: only 254, see below) hosts on each of the 2²¹ possible class C networks. Class C addresses are usually found at (small) companies.

  The CIDR notation for an class C network with it's 24 network bits is an "/24".

• There are also other addresses, starting with "111". Those are used for special purposes (e. g. multicast-addresses) and are not of interrest here.

Please note that the bits which are used for identifying the network-class are part of the network-address.

When seperating host-addresses from network-addresses, the "netmask" comes in handy. In this mask, all the network-bits are set to "1", the host-bits are "0". Thus, putting together IP-address and netmask with a locical AND-function, the network-address remains.

To continue our example, 255.255.0.0 is a possible netmask for 132.199.15.99. When applying this mask, the network-address 132.199.0.0 remains.

For addresses in CIDR notation, the number of network-bits given also says how many of the most significant bits of the address must be set to "1" to get the netmask for the corresponding network. For classfull addressing, every network-class has a fixed default netmask assigned:

• Class A (/8): default-netmask: 255.0.0.0, first byte of address: 1-127

• Class B (/16): default-netmask: 255.255.0.0, first byte of address: 128-191

• Class C (/24): default-netmask: 255.255.255.0, first byte of address: 192-223

Another thing to mention here is the "broadcast-address". When sending to this address, all hosts on the corresponding network will receive the message sent. The broadcast address is characterized by having all host-bits set to "1".

Taking 132.199.15.99 with its netmask 255.255.0.0 again, the broadcast-address would result in 132.199.255.255.

You'll ask now: But what if I want a hosts address to be all bits "0" or "1"? Well, this doesn't work, as network- and broadcast-address must be present! Because of this, a class B (/16) network can contain at most 2¹⁶-2 hosts, a class C (/24) network can hold no more than 2⁸-2 = 254 hosts.

Besides all those categories of addresses, there's the special IP-address 127.0.0.1 which always refers to the "local" host, i. e. if you talk to 127.0.0.1 you'll talk to yourself without starting any network-activity. This is sometimes useful to use services installed on your own machine or to play around if you don't have other hosts to put on your network.

Let's put together the things we've introduced in this section:

• IP-address: 32 bit-address, with network- and host-bits.

• Network-address: IP-address with all host bits set to "0".

• Netmask: 32-bit mask with "1" for network- and "0" for host-bits.

• Broadcast: IP-address with all host bits set "1".

• The local host's IP address is always 127.0.0.1.

9.1.5. Subnetting and Routing

After talking so much about netmasks, network-, host- and other addresses, I have to admit that this is not the whole truth.

Imagine the situation at your university, which usually has a class B (/16) address, allowing it to have up to 2¹⁶ ~= 65534 hosts on that net. Maybe it would be a nice thing to have all those hosts on one single network, but it's simply not possible due to limitations in the transport media commonly used today.

For example, when using thinwire ethernet, the maximum length of the cable is 185 meters. Even with repeaters in between, which refresh the signals, this is not enough to cover all the locations where machines are located. Besides that, there is a maximum number of 1024 hosts on one ethernet wire, and you'll loose quite a bit of performance if you go to this limit.

So, are you hosed now? Having an address which allows more than 60000 hosts, but being bound to media which allows far less than that limit?

Well, of course not! :-)

The idea is to divide the "big" class B net into several smaller networks, commonly called sub-networks or simply subnets. Those subnets are only allowed to have, say, 254 hosts on them (i.e. you divide one big class B network into several class C networks!).

To do this, you adjust your netmask to have more network- and less host-bits on it. This is usually done on a byte-boundary, but you're not forced to do it there. So, commonly your netmask will not be 255.255.0.0 as supposed by a class B network, but it will be set to 255.255.255.0.

In CIDR notation, you now write a "/24" instead of the "/16" to show that 24 bits of the address are used for identifying the network and subnet, instead of the 16 that were used before.

This gives you one additional network-byte to assign to each (physical!) network. All the 254 hosts on that subnet can now talk directly to each other, and you can build 256 such class C nets. This should fit your needs.

To explain this better, let's continue our above example. Say our host 132.199.15.99 (I'll call him dusk from now; we'll talk about assigning hostnames later) has a netmask of 255.255.255.0 and thus is on the subnet 132.199.15.0/24. Let's furthermore introduce some more hosts so we have something to play around with, see Figure 9-1.

In the above network, dusk can talk directly to dawn, as they are both on the same subnet. (There are other hosts attached to the 132.199.15.0/24-subnet but they are not of importance for us now)

But what, if dusk wants to talk to a host on another subnet?

Well, the traffic will then go through one or more gateways (routers), which are attached to two subnets. Because of this, a router always has two different addresses, one for each of the subnets it is on. The router is functionally transparent, i. e. you don't have to address it to reach hosts on the "other" side. Instead, you address that host directly and the packets will be routed to it correctly.

Example. Let's say dusk wants to get some files from the local ftp-server. As dusk can't reach ftp directly (because it's on a different subnet), all its packets will be forwarded to it's "defaultrouter" rzi (132.199.15.1), which knows where to forward the packets to.

Dusk knows the address of it's defaultrouter in its network (rzi, 132.199.15.1), and it will forward any packets to it which are not on the same subnet, i.e. it will forward all IP-packets in which the third address-byte isn't 15.

The (default)router then gives the packets to the appropriate host, as it's also on the FTP-server's network.

In this example, all packets are forwarded to the 132.199.1.0/24-network, simply because it's the network's backbone, the most important part of the network, which carries all the traffic that passes between several subnets. Almost all other networks besides 132.199.15.0/24 are attached to the backbone in a similar manner.

But what, if we had hooked up another subnet to 132.199.15.0/24 instead of 132.199.1.0/24? Maybe something the situation displayed in Figure 9-2.

When we now want to reach a host which is located in the 132.199.16.0/24-subnet from dusk, it won't work routing it to rzi, but you'll have to send it directly to route2 (132.199.15.2). Dusk will have to know to forward those packets to route2 and send all the others to rzi.

When configuring dusk, you tell it to forward all packets for the 132.199.16.0/24-subnet to route2, and all others to rzi. Instead of specifying this default as 132.199.1.0/24, 132.199.2.0/24, etc., 0.0.0.0 can be used to set the default-route.

Returning to Figure 9-1, there's a similar problem when dawn wants to send to noon, which is connected to dusk via a serial line running. When looking at the IP-addresses, noon seems to be attached to the 132.199.15.0-network, but it isn't really. Instead, dusk is used as gateway, and dawn will have to send its packets to dusk, which will forward them to noon then. The way dusk is forced into accepting packets that aren't destined at it but for a different host (noon) instead is called "proxy arp".

The same goes when hosts from other subnets want to send to noon. They have to send their packets to dusk (possibly routed via rzi),

9.1.6. Name Service Concepts

In the previous sections, when we talked about hosts, we referred to them by their IP-addresses. This was necessary to introduce the different kinds of addresses. When talking about hosts in general, it's more convenient to give them "names", as we did when talking about routing.

Most applications don't care whether you give them an IP address or an hostname. However, they'll use IP addresses internally, and there are several methods for them to map hostnames to IP addresses, each one with its own way of configuration. In this section we'll introduce the idea behind each method, in the next chapter, we'll talk about the configuration-part.

The mapping from hostnames (and domainnames) to IP-addresses is done by a piece of software called the "resolver". This is not an extra service, but some library routines which are linked to every application using networking-calls. The resolver will then try to resolve (hence the name ;-) the hostnames you give into IP addresses. See [RFC1034] and [RFC1035] for details on the resolver.

Hostnames are usually up to 10 characters long, and contain letters, numbers, dashes ("-") and underscores ("_"); case is ignorred.

Just as with networks and subnets, it's possible (and desirable) to group hosts into domains and subdomains. When getting your network-address, you usually also obtain a domainname by your provider. As with subnets, it's up to you to introduce subdomains. Other as with IP-addresses, (sub)domains are not directly related to (sub)nets; for example, one domain can contain hosts from several subnets.

Figure 9-1 shows this: Both subnets 132.199.1.0/24 and 132.199.15.0/24 (and others) are part of the subdomain "rz.uni-regensburg.de". The domain the University of Regensburg got from it's IP-provider is "uni-regensburg.de" (".de" is for Deutschland, Germany), the subdomain "rz" is for Rechenzentrum, computing center.

Hostnames, subdomain- and domainnames are separated by dots ("."). It's also possible to use more than one stage of subdomains, although this is not very common. An example would be fox_in.socs.uts.edu.au.

A hostname which includes the (sub)domain is also called a fully qualified domain name (FQDN). For example, the IP-address 132.199.15.99 belongs to the host with the FQDN dusk.rz.uni-regensburg.de.

Further above I told you that the IP-address 127.0.0.1 always belongs to the local host, regardless what's the "real" IP-address of the host. Therefore, 127.0.0.1 is always mapped to the name "localhost".

The three different ways to translate hostnames into IP addresses are: /etc/hosts, the Domain Name Service (DNS) and the Network Information Service (NIS).

IP-address        hostname [nickname [...]]
        

9.1.7. Next generation Internet protocol - IPv6

  127.0.0.1 

fe80::2a0:d2ff:fea5:e9f5 

10.0.0.0/24 

2001:638:a01:2::/64 

01:23:45:67:89:ab 

03:23:45:ff:fe:67:89:ab 

::0323:45ff:fe67:89ab 

127.0.0.1               localhost
::1                     localhost
          

noon            IN      AAAA    3ffe:400:430:2:240:95ff:fe40:4385

zone "0.3.4.0.0.0.4.0.e.f.f.3.IP6.INT" {
        type master;
        file "db.reverse";
}; 

5.8.3.4.0.4.e.f.f.f.5.9.0.4.2.0.2.0.0.0 IN   PTR   noon.ipv6.example.com.
          

9.2.1. A walk throught the kernel configuration

Before we dive into configuring various aspects of network setup, we want to walk through the necessary bits that have to or can be present in the kernel. See Chapter 7 for more details on compiling the kernel, we will concentrate on the configuration of the kernel here. We will take the i386/GENERIC config file as an example here. Config files for other platforms should contain similar information, the comments in the config files give additional hints. Besides the information given here, each kernel option is also documented in the options(4) manpage, and there is usually a manpage for each driver too, e.g. tlp(4).

      
#       $NetBSD: GENERIC,v 1.354.2.15 2001/05/06 15:18:54 he Exp $
      

The first line of each config file shows the version, which is 1.354.2.15 here. It can be used to compare against other versions via CVS, or when reporting bugs.

options         NTP             # NTP phase/frequency locked loop
      

If you want to run the Network Time Protocol (NTP), this option can be enabled for maximum precision. If the option is not present, NTP will still work. See ntpd(8) for more information.

file-system     NFS             # Network File System client
      

If you want to use another machine's harddisk via the Network File System (NFS), this option is needed. Section 9.3.2 gives more information on NFS.

options         NFSSERVER       # Network File System server
      

This option includes the server side of the NFS remote file sharing protocol. Enable if you want to allow other machines to use your harddisk. Section 9.3.2 contains more information on NFS.

#options        GATEWAY         # packet forwarding
      

If you want to setup a router that forwards packets between networks or network interfaces, setting this option is needed. If doesn't only switch on packet forwarding, but also increases some buffers. See options(4) for details.

options         INET            # IP + ICMP + TCP + UDP
      

This enables the TCP/IP code in the kernel. Even if you don't want/use networking, you will still need this for machine-internal communication of subsystems like the X Window System. See inet(4) for more details.

options         INET6           # IPV6
      

If you want to use IPv6, this is your option. If you don't want IPv6, which is part of NetBSD since the 1.5 release, you can remove/comment out that option. See the inet6(4) manpage and Section 9.1.7 for more information on the next generation Internet protocol.

#options        IPSEC           # IP security
      

Includes support for the IPsec protocol, including key and policy management, authentication and compression. This option can be used without the previous option INET6, if you just want to use IPsec with IPv4, which is possible. See ipsec(4) for more information.

#options        IPSEC_ESP       # IP security (encryption part; define w/IPSEC)
      

This option is needed in addition to IPSEC if encryption is wanted in IPsec.

#options        MROUTING        # IP multicast routing
      

If multicast services like the MBone services should be routed, this option needs to be included. Note that the routing itself is controlled by the mrouted(8) daemon.

options         NS              # XNS
#options        NSIP            # XNS tunneling over IP
      

These options enables the Xerox Network Systems(tm) protocol family. It's not related to the TCP/IP protocol stack, and in rare use today. The ns(4) manpage has some details.

options         ISO,TPIP        # OSI
#options        EON             # OSI tunneling over IP
      

These options include the OSI protocol stack, that was said for a long time to be the future of networking. It's mostly history these days. :-) See the iso(4) manpage for more information.

options         CCITT,LLC,HDLC  # X.25
      

These options enable the X.25 protocol set for transmission of data over serial lines. It is/was used mostly in conjunction with the OSI protocols and in WAN networking.

options         NETATALK        # AppleTalk networking protocols
      

Include support for the AppleTalk protocol stack. Userland server programs are needed to make use of that. See pkgsrc/net/netatalk and pkgsrc/net/netatalk-asun for such packages. More information on the AppleTalk protocol and protocol stackk are available in the atalk(4) manpage.

options         PPP_BSDCOMP     # BSD-Compress compression support for PPP
options         PPP_DEFLATE     # Deflate compression support for PPP
options         PPP_FILTER      # Active filter support for PPP (requires bpf)
      

These options tune various aspects of the Point-to-Point protocol. The first two determine the compression algorithms used and available, while the third one enables code to filter some packets.

options         PFIL_HOOKS      # pfil(9) packet filter hooks
options         IPFILTER_LOG    # ipmon(8) log support
      

These options enable firewalling in NetBSD, using IPfilter. See the ipf(4) and ipf(8) manpages for more information on operation of IPfilter, and Section 9.3.1.1 for a configuration example.

# Compatibility with 4.2BSD implementation of TCP/IP.  Not recommended.
#options        TCP_COMPAT_42
      

This option is only needed if you have machines on the network that still run 4.2BSD or a network stack derived from it. If you've got one or more 4.2BSD-systems on your network, you've to pay attention to set the right broadcast-address, as 4.2BSD has a bug in its networking code, concerning the broadcast address. This bug forces you to set all host-bits in the broadcast-address to "0". The TCP_COMPAT_42 option helps you ensuring this.

options         NFS_BOOT_DHCP,NFS_BOOT_BOOTPARAM
      

These options enable lookup of data via DHCP or the BOOTPARAM protocol if the kernel is told to use a NFS root file system. See the diskless(8) manpage for more information.

# Kernel root file system and dump configuration.
config          netbsd  root on ? type ?
#config         netbsd  root on sd0a type ffs
#config         netbsd  root on ? type nfs
      

These lines tell where the kernel looks for it's root file system, and which filesystem type it is expected to have. If you want to make a kernel that uses a NFS root filesystem via the tlp0 interface, you can do this with "root on tlp0 type nfs". If a ? is used instead of a device/type, the kernel tries to figure one out on it's own.

# ISA serial interfaces
com0    at isa? port 0x3f8 irq 4        # Standard PC serial ports
com1    at isa? port 0x2f8 irq 3
com2    at isa? port 0x3e8 irq 5
      

If you want to use PPP or SLIP, you will need some serial (com) interfaces. Others with attachment on USB, PCMCIA or PUC will do as well.

# Network Interfaces
      

This rather long list contains all sort of network drivers. Please pick the one that matches your hardware, according to the comments. For most drivers, there's also a manual page available, e.g. tlp(4), ne(4), etc.

# MII/PHY support
      

This section lists media independent interfaces for network cards. Pick one that matches your hardware. If in doubt, enable them all and see what the kernel picks. See the mii(4) manpage for more information.

# USB Ethernet adapters
aue*    at uhub? port ?         # ADMtek AN986 Pegasus based adapters
cue*    at uhub? port ?         # CATC USB-EL1201A based adapters
kue*    at uhub? port ?         # Kawasaki LSI KL5KUSB101B based adapters
      

USB-ethernet adapters only have about 2MBit/s bandwidth, but they are very convenient to use. Of course this needs other USB related options which we won't cover here, as well as the necessary hardware. See the corresponding manpages for more information.

# network pseudo-devices
pseudo-device   bpfilter        8       # Berkeley packet filter
      

This pseudo-device allows sniffing packets of all sorts. It's needed for tcpdump, but also rarpd and some other applications that need to know about network traffic. See bpf(4) for more information.

pseudo-device   ipfilter                # IP filter (firewall) and NAT
      

This one enables the IPfilter's packet filtering kernel interface used for firewalling, NAT (IP Masquerading) etc. See ipf(4) and Section 9.3.1.1 for more information.

pseudo-device   loop                    # network loopback
      

This is the "lo0" software loopback network device which is used by some programs these days, as well as for routing things. Should not be omited. See lo(4) for more details.

pseudo-device   ppp             2       # Point-to-Point Protocol
      

If you want to use PPP either over a serial interface or ethernet (PPPoE), you will need this option. See ppp(4) for details on this interface.

pseudo-device   sl              2       # Serial Line IP
      

Serial Line IP is a simple encapsulation for IP over (well :) serial lines. It does not include negotiation of IP addresses and other options, which is the reason that it's not in widespread use today any more. See sl(4).

pseudo-device   strip           2       # Starmode Radio IP (Metricom)
      

If you happen to have one of the old Metricon Ricochet packet radio wireless network devices, use this pseudo-device to use it. See the strip(4) manpage for detailled information.

pseudo-device   tun             2       # network tunneling over tty
      

This network device can be used to tunnel network packets to a device file, /dev/tun*. Packets routed to the tun0 interface can be read from /dev/tun0, and data written to /dev/tun0 will be sent out the tun0 network interface. This can be used to implement e.g. QoS routing in userland. See tun(4) for details.

pseudo-device   gre             2       # generic L3 over IP tunnel
      

The GRE encapsulation can be used to tunnel arbitrary layer 3 packets over IP, e.g. to implement VPNs. See gre(4) for more.

pseudo-device   ipip            2       # IP Encapsulation within IP (RFC 2003)
      

Another IP-in-IP encapsulation device, with a different encapsulation format. See the ipip(4) manpage for details.

pseudo-device   gif             4       # IPv[46] over IPv[46] tunnel (RFC 1933)
      

Using the GIF interface allows to tunnel e.g. IPv6 over IPv4, which can be used to get IPv6 connectivity if no IPv6-capable uplink (ISP) is available. Other mixes of operations are possible, too. See the gif(4) manpage for some examples.

#pseudo-device  faith           1       # IPv[46] tcp relay translation i/f
      

The faith interface captures IPv6 TCP traffic, for implementing userland IPv6-to-IPv4 TCP relays e.g. for protocol transitions. See the faith(4) manpage for more details on this device.

#pseudo-device  stf             1       # 6to4 IPv6 over IPv4 encapsulation
      

This add a network device that can be used to tunnel IPv6 over IPv4 without setting up a configured tunnel before. The source address of outgoing packets contains the IPv4 address, which allows routing replies back via IPv4. See the stf(4) manpage and Section 9.3.4 for more details.

pseudo-device   vlan                    # IEEE 802.1q encapsulation
      

This interface provides support for IEEE 802.1Q Virtual LANs, which allows tagging Ethernet frames with a "vlan" ID. Using properly configured switchens (that also have to support VLAN, of course), this can be used to build virtual LANs where one set of machines doesn't see traffic from the other (broadcast and other). The vlan(4) manpage tells more about this.

9.2.2. Overview of the network configuration files

The following is a list of the files used to configure the network. The usage of these files, some of which have already been met the first chapters, will be described in the following sections.

9.2.3. Connecting to the Internet

There are many types of Internet connections: this section explains how to connect to a provider using a modem over a telephone line using the PPP protocol, a very common setup. In order to have a working connection, the following steps must be done:

Judging from the previous list it looks like a complicated procedure that requires a lot of work. Actually, the single steps are very easy: it's just a matter of modifying, creating or simply checking some small text files. In the following example it will be assumed that the modem is connected to the second serial port /dev/tty01 (COM2 in DOS.)

  nameserver 194.109.123.2
  nameserver 191.200.4.52
  #lookup file bind
          

  # /etc/nsswitch.conf
  group:         compat
  group_compat:  nis
  hosts:         files dns 
  netgroup:      files [notfound=return] nis
  networks:      files
  passwd:        compat
  passwd_compat: nis
          

  # /etc/ppp/peers/bignet
  connect '/usr/sbin/chat -v -f /etc/ppp/peers/bignet.chat'
  noauth
  user alan
  remotename bignet.it
          

  # /etc/ppp/peers/bignet.chat
  ABORT BUSY
  ABORT "NO CARRIER"
  ABORT "NO DIALTONE"
  '' ATDT0299999999
  CONNECT ''
        

  user * password
          

  alan * pZY9o
          

  # /etc/ppp/peers/bignet.chat
  ABORT BUSY
  ABORT "NO CARRIER"
  ABORT "NO DIALTONE"
  '' ATDT0299999999
  CONNECT ''
  TIMEOUT 50
  ogin: alan
  ssword: pZY9o
            

  /dev/tty01
  lock
  crtscts
  57600
  modem
  defaultroute
  noipdefault
          

  # pppd call bignet
        

  # tail -f /var/log/messages
        

  #!/bin/sh
  MODEM=tty01
  POP=bignet
  if [ -f /var/spool/lock/LCK..$MODEM ]; then
    echo ppp is already running...
  else
    pppd call $POP
    tail -f /var/log/messages
  fi
          

  #!/bin/sh
  MODEM=tty01
  if [ -f /var/spool/lock/LCK..$MODEM ]; then
    echo -f killing pppd...
    kill -HUP `cat /var/spool/lock/LCK..$MODEM`
    echo done
  else
    echo ppp is not active
  fi
          

  # chmod u+x ppp-up ppp-down
        

9.2.4. Creating a small home network

Networking is one of the main strengths of Unix and NetBSD is no exception: networking is both powerful and easy to set up and inexpensive too, because there is no need to buy additional software to communicate or to build a server. Section 9.3.1 explains how to configure a NetBSD machine to act as a gateway for a network: with IPNAT all the hosts of the network can reach the Internet with a single connection to a provider made by the gateway machine. The only thing to be checked before creating the network is to buy network cards supported by NetBSD (check the INSTALL file for a list of supported devices.)

First, the network cards must be installed and connected to a hub, switch or directly (see Figure 9-6.)

Next, check that the network cards are recognized by the kernel, studying the output of the dmesg command. In the following example the kernel recognized correctly an NE2000 clone:

  ...
  ne0 at isa0 port 0x280-0x29f irq 9
  ne0: NE2000 Ethernet
  ne0: Ethernet address 00:c2:dd:c1:d1:21
  ...
      

If the card is not recognized by the kernel, check that it is enabled in the kernel configuration file and then that the card's IRQ matches the one that the kernel expects. For example, this is the isa NE2000 line in the configuration file; the kernel expects the card to be at IRQ 9.

...
ne0 at isa? port 0x280 irq 9 # NE[12]000 ethernet cards
...
      

If the card's configuration is different, it will probably not be found at boot. In this case, either change the line in the kernel configuration file and compile a new kernel or change the card's setup (usually through a setup disk or, for old cards, a jumper on the card.)

The following command shows the network card's current configuration:

# ifconfig ne0
ne0: flags=8822<BROADCAST,NOTRAILERS,SIMPLEX,MULTICAST> mtu 1500 media: Ethernet 10base2
      

The software configuration of the network card is very easy. The IP address "192.168.1.1" (which is reserved for internal networks) is assigned to the card.

# ifconfig ne0 inet 192.168.1.1 netmask 0xffffff00
      

Repeating the previous command now gives a different result:

# ifconfig ne0
ne0: flags=8863<UP,BROADCAST,NOTRAILERS,RUNNING,SIMPLEX,MULTICAST> mtu 1500
          media: Ethernet 10base2
          inet 192.168.1.1 netmask 0xffffff00 broadcast 192.168.1.255
      

The output of ifconfig has now changed: the IP address is now printed and there are two new flags, "UP" and "RUNNING". If the interface isn't "UP", it will not be used by the system to send packets.

The host was given the IP address 192.168.1.1, which belongs to the set of addresses reserved for internal networks which are not reachable from the Internet. The configuration is finished and must now be tested; if there is another active host on the network, a ping can be tried. For example, if 192.168.1.2 is the address of the active host:

  # ping 192.168.1.2
  PING ape (192.168.1.2): 56 data bytes
  64 bytes from 192.168.1.2: icmp_seq=0 ttl=255 time=1.286 ms
  64 bytes from 192.168.1.2: icmp_seq=1 ttl=255 time=0.649 ms
  64 bytes from 192.168.1.2: icmp_seq=2 ttl=255 time=0.681 ms
  64 bytes from 192.168.1.2: icmp_seq=3 ttl=255 time=0.656 ms
  ^C
  ----ape PING Statistics----
  4 packets transmitted, 4 packets received, 0.0% packet loss
  round-trip min/avg/max/stddev = 0.649/0.818/1.286/0.312 ms
      

With the current setup, at the next boot it will be necessary to repeat the configuration of the network card. In order to avoid repeating the card's configuration at each boot, two things need to be done: first, create the file /etc/ifconfig.ne0 containing the following line:

  inet 192.168.1.1 netmask 0xffffff00
      

Next, in the /etc/rc.conf file, set the following option

  auto_ifconfig=YES
      

At the next boot the network card will be configured automatically.

The /etc/hosts file is a database of IP addresses and textual aliases: it should contain the addresses of all the hosts belonging to the internal network. For example:

#     $NetBSD: hosts,v 1.4 1997/01/09 05:33:14 mikel Exp $
#
# Host Database
# This file should contain the addresses and aliases
# for local hosts that share this file.
# It is used only for "ifconfig" and other operations
# before the nameserver is started.
#
#
127.0.0.1             localhost
#
# RFC 1918 specifies that these networks are "internal".
# 10.0.0.0    10.255.255.255
# 172.16.0.0  172.31.255.255
# 192.168.0.0 192.168.255.255

192.168.1.1   ape.insetti.net ape
192.168.1.2   vespa.insetti.net vespa
192.168.1.0   insetti.net
        

The /etc/nsswitch.conf should be modified as explained in Example 9-2.

Summing up, to configure the network the following must be done: the network adapters must be installed and physically connected. Next they must be configured (with ifconfig) and, finally, the /etc/hosts and /etc/nsswitch.conf files must be modified. This type of network management in very simplified and is suited only for small networks without sophisticated needs.

9.2.5. Connecting two PCs through a serial line

If you need to transfer files between two PCs which are not networked there is a simple solution which is particularly handy when copying the files to a floppy is not practical: the two machines can be networked with a serial cable (a null modem cable.) The following sections describe some configurations.

  # slattach /dev/tty00
  # ifconfig sl0 inet 192.168.1.1 192.168.1.2
        

  # slattach /dev/tty00
  # ifconfig sl0 inet 192.168.1.2 192.168.1.1
        

  # ping 192.168.1.1
        

  connect '/usr/sbin/chat -v CLIENT CLIENTSERVER'
  local
  tty00  
  115200
  crtscts
  lock   
  noauth
  nodefaultroute
  :192.168.1.2
        

9.3.1. IPNAT

The mysterious acronym IPNAT hides the Internet Protocol Network Address Translation, which enables the routing of an internal network on a real network (Internet.) This means that with only one "real" IP, static or dynamic, belonging to a gateway running IPNAT, it is possible to create simultaneous connections to the Internet for all the hosts of the internal network.

Some usage examples of IPNAT can be found in the subdirectory /usr/share/examples/ipf: look at the files BASIC.NAT and nat-setup.

The setup for the example described in this section is detailed in Figure 9-6: host 1 can connect to the Internet calling a provider with a modem and getting a dynamic IP address. host 2 and host 3 can't communicate with the Internet with a normal setup: IPNAT allows them to do it: host 1 will act as a gateway for hosts 2 and 3.

  # sysctl net.inet.ip.forwarding
  net.inet.ip.forwarding = 1
        

map ppp0 192.168.1.0/24 -> 0/32 proxy port ftp ftp/tcp
map ppp0 192.168.1.0/24 -> 0/32 portmap tcp/udp 40000:60000
map ppp0 192.168.1.0/24 -> 0/32
        

#!/bin/sh
# /etc/ppp/ip-up
/etc/rc.d/ipnat forcestart
        

#!/bin/sh
# /etc/ppp/ip-down
/etc/rc.d/ipnat forcestop
        

  # chmod u+x ip-up ip-down
        

  # route add default 192.168.1.1
        

9.3.2. NFS

Now that the network is working it is possible to share files and directories over the network using NFS. From the point of view of file sharing, the computer which gives access to its files and directories is called the server, and the computer using these files and directories is the client. A computer can be client and server at the same time.

• A kernel must be compiled with the appropriate options for the client and the server (the options are easy to find in the kernel configuration file. See Section 9.2.1 for more information on NFS related kernel options.

• The server must enable its RPC services in /etc/inetd.conf.

• In /etc/rc.conf the server must enable the inetd and portmap daemons and the nfs_server option.

• In /etc/rc.conf the client must enable inetd and nfs_client.

• The server must list the exported directories in /etc/exports and then run the command kill -HUP `cat /var/run/mountd.pid.

A client host can access a remote directory through NFS if:

• The server host exports the directory.

• The client host mounts the remote directory with the command mount server:/xx/yy /mnt

The mount command has a rich set of options for remote directories which are not very intuitive (to say the least.)

  /dev/ra0a on /
  /dev/ra0f on /usr
  /dev/ra1a on /usr/src
  /dev/ra2a on /export
        

  buzz:/export/cli?/root on /
  buzz:/export/common/usr on /usr
  buzz:/usr/src on /usr/src
        

  # /etc/exports
  /usr/src -network 123.45.67.0 -mask 255.255.255.0
  /export  -alldirs -maproot=root -network 123.45.67.0 -mask 255.255.255.0
        

  buzz:/export/cli?/root / nfs rw
  buzz:/export/common/usr /usr nfs rw,nodev,nosuid
  buzz:/usr/src /usr/src rw,nodev,nosuid
        

9.3.3. Setting up /net with amd

  % showmount -e wuarchive.wustl.edu
  Exports list on wuarchive.wustl.edu:
  /export/home                       onc.wustl.edu 
  /export/local                      onc.wustl.edu 
  /export/adm/log                    onc.wustl.edu 
  /usr                               onc.wustl.edu 
  /                                  onc.wustl.edu 
  /archive                           Everyone
        

  % cd /net/wuarchive.wustl.edu/archive/systems/unix/NetBSD
        

9.3.4. IPv6 Connectivity & Transition via 6to4

This section will concentrate on how to get network connectivity for IPv6 and - as that's still not easy to get native today - talk in length about the alternatives to native IPv6 connectivity as a transitional method until native IPv6 peers are available.

Finding an ISP that offers IPv6 natively needs quite some luck. What you need next is a router that will be able to handle the traffic. To date, not all router manufacturers offer IPv6 support for their machines, and even if they do, it's unlikely that they offer hardware accelerated IPv6 routing or switching. A rather cheap alternative to the router hardware commonly in use today is using a standard PC and configure it as a router, e.g. by using some Linux or BSD derived operating system like NetBSD, and use software like Zebra for handling the routing protocols. This solution is rather common today for sites that want IPv6 connectivity today. The drawbacks are that you need an ISP that supports IPv6, and that you need dedicated uplink only for IPv6.

If this is not an option for you, you can still get IPv6 connectivity by using tunnels. Instead of talking IPv6 on the wire, the IPv6 packets are encapsulated in IPv4 packets, as shown in Figure 9-7. Using existing IPv4 infrastructure, the encapsulated packets are sent to a IPv6-capable uplink that will then remove the encapsulation, and forward the IPv6 packets via native IPv6.

When using tunnels, there are two possibilities. One is to use a so-called "configured" tunnel, the other is called an "automatic" tunnel. A "configured" tunnel is one that required preparation from both ends of the tunnel, usually connected with some kind of registration to exchange setup information. An example for such a configured tunnel is the IPv6-over-IPv4 encapsulation described in [RFC1933], and that's implemented e.g. by the gif(4) device found in NetBSD.

An "automatic" tunnel consists of a public server that has some kind of IPv6 connectivity, e.g. via 6Bone. That server has made it's connectivity data public, and also runs a tunneling protocol that does not require an explicit registration of the sites using it as uplink. A well-used example of such a protocol is the 6to4 mechanism described in [RFC3056], and that is implemented in the stf(4) device found in NetBSD's. Another mechanism that does not require registration of IPv6-information is the 6over4 mechanism, which implements transporting of IPv6 over a multicast-enabled IPv4 network, instead of e.g. ethernet or FDDI. 6over4 is documented in [RFC2529]. It's main drawback is that you do need existing multicast infrastructure. If you don't have that, setting it up is about as much effort as setting up a configured IPv6 tunnel directly, so it's usually not worth bothering in that case.

  options INET6                 # IPv6
  pseudo-device stf             # 6to4 IPv6 over IPv4 encapsulation

  # ifconfig stf0 inet6 2002:3ee0:3972:1::1 prefixlen 16 alias  (local) 

  # route add -inet6 default 2002:cdb2:5ac2::1 (remote)

  # /sbin/ping6 www.kame.net

  ifconfig ne0 inet6 alias 2002:3ee0:3972:2:1234:56ff:fe78:9abc	

  # sysctl -w net.inet6.ip6.forwarding=1 

  # rtadvd