ndb – Network database


The network database consists of files describing machines known to the local installation and machines known publicly. The files comprise multi–line tuples made up of attribute/value pairs of the form attr=value or sometimes just attr. Each line starting without white space starts a new tuple. Lines starting with # are comments.

The file /lib/ndb/local is the root of the database. Other files are included in the database if a tuple with an attribute–value pair of attribute database and no value exists in /lib/ndb/local. Within the database tuple, each pair with attribute file identifies a file to be included in the database. The files are searched in the order they appear. For example:

declares the database to be composed of the three files /lib/ndb/common, /lib/ndb/local, and /lib/ndb/global. By default, /lib/ndb/local is searched before the others. However, /lib/ndb/local may be included in the database to redefine its ordering.

Within tuples, pairs on the same line bind tighter than pairs on different lines.

Programs search the database directly using the routines in ndb(2) or indirectly using ndb/cs and ndb/dns (see ndb(8)). Both ndb/cs and the routine ndbipinfo impose structure on the otherwise flat database by using knowledge specific to the network. The internet is made up of networks which can be subnetted multiple times. A network must have an ipnet attribute and is uniquely identified by the values of its ip and ipmask attributes. If the ipmask is missing, the relevant Class A, B or C one is used.

A search for an attribute associated with a network or host starts at the lowest level, the entry for the host or network itself, and works its way up, bit by bit, looking at entries for nets/subnets that include the network or host. The search ends when the attribute is found. For example, consider the following entries:
ipnet=murray–hill ip= ipmask=
ipnet=plan9 ip= ipmask=
ip= sys=anna dom=anna.cs.bell–

Here anna is on the subnet plan9 which is in turn on the class B net murray–hill. Assume that we're searching for anna's NTP and SMTP servers. The search starts by looking for an entry with sys=anna. We find the anna entry. Since it has an smtp=smtp2.cs.bell– pair, we're done looking for that attribute. To fulfill the NTP request, we continue by looking for networks that include anna's IP address. We lop off the right most one bit from anna's address and look for an ipnet= entry with ip= Not finding one, we drop another bit and look for an ipnet= entry with ip= There is such an entry and it has the pair, ntp=oncore.cs.bell–, ending our search.

Ndb/cs can be made to perform such network aware searches by using metanames in the dialstring. A metaname is a $ followed by an attribute name. Ndb/cs looks up the attribute relative to the system it is running on. Thus, with the above example, if a program called
dial("tcp!$smtp!smtp", 0, 0, 0);

the dial would connect to the SMTP port of smtp2.cs.bell–

A number of attributes are meaningful to programs and thus reserved. They are:
sys         system name (a short name)
dom         Internet fully–qualified domain name
ip          Internet address, v4 or v6.
ipv6        IPv6 Internet address. For DNS, an AAAA record.
ether       Ethernet address (must be lower–case hexadecimal). Beware that for machines with multiple ether attributes, dhcpd may expect requests to come from the address in the first ether attribute.
bootf       file to download for initial bootstrap; /386/9boot to boot a PC via PXE.
ipnet       Internet network name
ipmask      Internet network mask
ipgw        Internet gateway
auth        authentication server to be used
authdom     authentication domain. Plan 9 supports multiple authentication domains. To specify an authentication server for a particular domain, add a tuple containing both auth and authdom attributes and values.
fs          file server to be used
tcp         a TCP service name
udp         a UDP service name
port        a TCP or UDP port number
restricteda TCP service that can be called only by ports numbered less that 1024
proto       a protocol supported by a host. The pair proto=il was needed by cs (see ndb(8)) in tuples for hosts that supported the IL protocol
dnsdomain   a domain name that ndb/dns adds onto any unrooted names when doing a search. There may be multiple dnsdomain pairs.
dns         a DNS server to use (for DNS and DHCP)
ntp         an NTP server to use (for DHCP)
smtp        an SMTP server to use (for DHCP)
time        a time server to use (for DHCP)
wins        a Windows name server (for DHCP)
mx          mail exchanger (for DNS and DHCP); also pref.
srv         service location (for DNS); also pri, weight and port.
soa         start of area (for DNS)

Cs defers to dns to translate dotted names to IP addresses, only consulting the database files if dns cannot translate the name.

Cs allows network entries with sys and dom attributes but no ip attribute. Searches for the system name are resolved by looking up the domain name with dns.

The file /lib/ndb/auth is used during authentication to decide who has the power to `speak for' other users; see authsrv(6).


A tuple for the CPU server, spindle.

ip= ether=080069020677

Entries for the network mh–astro–net and its subnets.

ipnet=mh–astro–net ip= ipmask=
ipnet=unix–room ip=
ipnet=third–floor ip=

Mappings between TCP service names and port numbers.

tcp=sysmon       port=401
tcp=rexec        port=512     restricted
tcp=9fs          port=564

/lib/ndb/local   first database file searched

con(1), dial(2), ndb(2), 9boot(8), booting(8), dhcpd(8), ipconfig(8), ndb(8)
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