The named.local File The named.cache file

The SOA record defines very important file parameters: Serial number of the file — every time the file is updated the serial should be increased • Refresh time — the time period in seconds that secondary servers must query the primary server for possible changes update of the file • Retry time — the time period in seconds that the secondary server must retry its query if the previous one did not succeed • Expire time — the time period in seconds that the database is considered as the actual one after the primary name server has stopped running and does not respond to any query • Minimum TTL — default time−to−live of records stored in the cache • It is extremely important to increase the serial number after any update of the named.hosts file. For secondary name servers, this is the only sign that the file has been updated. When querying the primary server, a secondary server actually checks the current serial of the file; after comparing this value with the serial of the files copy that it already keeps, the decision about the files transfer is made. Obviously any file update without a serial number increase is useless, because it will not be spread toward secondary servers. It can be useful to implement the current date as the serial number for a current file update, in order to continue the increasing order of the sequence of serials. A serial is a 32−bit number up to 4 billion, so even the full date is acceptable. An example is presented for the update done on May 23, 2000: 2000052302 The last two digits are a daily version — the second version for this day

16.3.1.3.2 The named.local File

The only purpose of the named.local file is to convert the IP address 127.0.0.1 the loopback address into the generic name localhost. This is the zone file for the reverse domain 0.0.127.in−addr.arpa. Because all systems use the same loopback address, this file is identical on every server. Also, every server has authority over its loopback address; every server is the primary server for its loopback address. The named.local file is shown below: cat varnamednamed.local ; −−−−−−−−−−−−−−−−−−−−−−−− varnamednamed.local −−−−−−−−−−−−−−−−−−−−−−−−−− ; IN SOA patsy.myschool.scps.edu. sajhc.cunyvm.myschool.scps.edu. 9704065 ; serial 10800 ; refresh every 3 hours 3600 ; retry every 1 hour 1209600 ; expire after 2 weeks 86400 ; default min. TTL value of 1 day ; IN NS pegasus.myschool.scps.edu. 1 IN PTR localhost. ;

16.3.1.3.3 The named.cache file

This is the cache initialization file for every server that maintains a cache of domain data; it contains the information needed to begin building such a domain when the name server starts. The named.cache file contains the names and addresses of the root servers. An example of 387 cat varnamednamed.cache ; −−−−−−−−−−−−−−−−−−−−− varnamednamed.cache −−−−−−−−−−−−−−−−−−−−− ; ; root.cache 1.15 Berkeley 890918 ; . 99999999 IN NS NS.NIC.DDN.MIL. 99999999 IN NS NS.NASA.GOV. 99999999 IN NS TERP.UMD.EDU. 99999999 IN NS KAVA.NISC.SRI.COM. 99999999 IN NS AOS.ARL.ARMY.MIL. 99999999 IN NS NIC.NORDU.NET. 99999999 IN NS C.NYSER.NET. 99999999 IN NS NS.INTERNIC.NET. ; ; ; ; ; Root domain servers adresses ; NS.NIC.DDN.MIL. 99999999 IN A 192.112.36.4 NS.NASA.GOV. 99999999 IN A 128.102.16.10 99999999 IN A 192.52.195.10 TERP.UMD.EDU. 99999999 IN A 128.8.10.90 KAVA.NISC.SRI.COM. 99999999 IN A 192.33.33.24 AOS.ARL.ARMY.MIL. 99999999 IN A 128.63.4.82 99999999 IN A 192.5.25.82 NIC.NORDU.NET. 99999999 IN A 192.36.148.17 C.NYSER.NET. 99999999 IN A 192.33.4.12 NS.INTERNIC.NET. 99999999 IN A 198.41.0.4 ; The file contains only NS and A records. The root domain is indicated by a single dot. First, a set of NS records identifies the name servers for the root domain, and then a set of A records defines the IP addresses for those root name servers. Traditionally, TTL is set to the largest possible value 99999999 the root servers are never removed from the cache. Although the root name servers do not change often, it is recommended that you periodically check the accuracy of these data. An accurate list of root servers is available via anonymous ftp from NIC.DDN.MIL host, in the file netinforoot−servers.txt.

16.3.1.3.4 The Reverse Domain File: named.in−addr