134. Version A.01 H3065S Module 12 Slides
DNS Name Resolution
Version A.01
H3065S Module 12 Slides

135. Resolving Host Names to IP Addresses
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Resolving Host Names to IP Addresses
BIND
Resolving
host names to IP
addresses
NIS/NIS+
/etc/hosts
hosts Map
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136. DNS Overview Hierarchical Name Space Components of DNS Name Resolvers
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DNS Overview
Hierarchical
Name Space
Components of
DNS
Name
Resolvers
Servers
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137. The DNS Hierarchical Name Space
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The DNS Hierarchical Name Space .
" root "
edu
gov
com
acme hp
ibm il ca ny
chicago
sanfran
nyc
peoria
oakland
albany
rockford la
buffalo
Legend:
domain
host
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138. Public and Private Name Spaces
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Public and Private Name Spaces . .
com
edu
com
gov hp
acme hp
ibm il ga ny il ca ny
chicago
atlanta
nyc
chicago
sanfran
nyc
peoria
athens
albany
peoria
oakland
albany
rockford
macon
buffalo
rockford la
buffalo
Public Name Space
Private Name Space
Public Name space is connected to the public internet.
Organizations/companies are delegated responsibility for names/IPs within their domains.
Private name space is not connected to the public internet.
Organizations/companies can manage namespace as desired.
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139. in-addr.arpa Name Space
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in-addr.arpa Name Space .
arpa
com
in-addr hp
. . . 1
128
. . .
254 ca
. . .
. . . 1
255
sanfran
oakland la
. . . 1
. . .
255 1 2 3
sanfran oakland la
sanfran.ca.hp.com = in-addr.arpa.
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140. Name Servers A DNS name server
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Name Servers
A DNS name server
resolves IP addresses to host names for clients
is delegated authority over a portion of the name space
can delegate authority to other name servers
should have a secondary name server as a backup
Example
ca.hp.com name server
sanfran.ca.hp.com
oakland.ca.hp.com
la.ca.hp.com
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141. . . . . . . . . . . . . . . Name Server Zones hp.com Zone
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Name Server Zones . . . .
com
edu
gov
hp.com Zone . hp
corp ca az il ga wa ny tx nc
Delegated Subdomains
hp.com domain
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142. Resolving Host Names in the Local Domain
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Resolving Host Names in the Local Domain
ca.hp.com NS
la.ca.hp.com?
la =
oakland.ca.hp.com
# telnet la.ca.hp.com
sanfran
oakland la
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143. Resolving Host Names in Other Domains
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Resolving Host Names in Other Domains
atlanta.ga.hp.com?
go to com. NS!
. NS
atlanta.ga.hp.com?
com. NS
oakland
ca.hp.com NS
go to hp.com. NS!
atlanta.ga.hp.com?
atlanta.ga.hp.com?
hp.com. NS
go to ga.hp.com. NS!
atlanta.ga.hp.com?
atlanta =
oakland# telnet atlanta.ga.hp.com
ga.hp.com. NS
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144. Configuring a Primary Name Server
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Configuring a Primary Name Server 1. 2. 3. 4. 5. 6. 7. 8.
Notify the internic of your new subdomain.
Fully qualify host names in /etc/hosts.
Create a directory for the DNS database files.
Create a parameter file for hosts_to_named.
Create the DNS data and boot files with hosts_to_named.
Download a db.cache file with pointers to the root servers.
Modify /etc/rc.config.d/namesvrs and start the named daemon.
Configure DNS client functionality on the primary server.
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145. Configuring a Secondary Name Server
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Configuring a Secondary Name Server 1. 2. 3. 4. 5. 6.
Create a directory for the DNS data files.
FTP a boot configuration file from the primary.
FTP a copy of db and db.cache from the primary.
FTP additional DNS data files from the primary (optional).
Modify /etc/rc.config.d/namesvrs and start named.
Configure DNS client functionality on the secondary server.
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146. Configuring DNS Clients
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Configuring DNS Clients
1. Create /etc/resolv.conf
search ca.hp.com hp.com
nameserver
nameserver
2. Modify /etc/nsswitch.conf
hosts: dns nis files
3. Modify /etc/hosts
localhost
la.ca.hp.com la
4. Modify ~/.rhosts, /etc/hosts.equiv, and other files
la user1
la.ca.hp.com. user1
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147. Configuring the Name Service Switch
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Configuring the Name Service Switch
Q: Where should I look up host names?
DNS? /etc/hosts? NIS?
A: Check /etc/nsswitch.conf!
hosts: files
hosts: dns nis files
hosts: files [NOTFOUND=continue] dns
hosts: files [NOTFOUND=continue] nis or or or
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148. Testing DNS with nslookup
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Testing DNS with nslookup
# nslookup
> server # Choose a name server
> oakland.ca.hp.com # Resolve a hostname to an IP
> # Resolve an IP to a hostname
> exit
Name Server: sanfran.ca.hp.com
Address:
Trying DNS
Name: oakland.ca.hp.com
Address:
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149. 4/21/2017
DNS Boot and Data Files
/etc/named.data
/etc/named.boot on the primary ca.hp.com name server:
; Define the DNS data directory
directory /etc/named.data
; Define which domains this name server
; can serve, and which file contains the
; records for each of those domains. Note
; this name server is primary for all
; of the domains listed here.
primary ca.hp.com db.ca
primary in-addr.arpa db
primary in-addr.arpa db
cache db.cache
db.ca db db
db.cache
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150. Loading the DNS Data Files
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Loading the DNS Data Files
Ready to resolve host names!
named loads db files in cache
/etc/named.data/db.*
named decides which db files to load
/etc/named.boot
named starts at run level 2
/etc/rc.config.d/namesvrs
System boot initiated
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151. Updating the Primary Server
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Updating the Primary Server
1. Update /etc/hosts on the primary.
# vi /etc/hosts
2. Rebuild DNS data files with hosts_to_named.
# cd /etc/named.data
# hosts_to_named -f param
3. Reload DNS data files in cache with sig_named restart.
# sig_named restart
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152. Updating the Secondary Server
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Updating the Secondary Server
Q: How do I know if my DNS data files are up to date?
Q: When should I refresh my DNS data files?
Secondary Name Server
named Daemon
A: named consults a data file’s SOA record to determines if/when the file must be updated:
ca.hp.com. IN SOA sanfran.ca.hp.com root.sanfran.ca.hp.com (
; Retry every 1 hour
; Expire after 1 week
) ; Minimum TTL of 1 day
; Serial
; Refresh every 3 hours
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