Transcript TCP/IP Administration - Pravin Shetty > Resume

TCP/IP Administration
IP addresses & Names
DNS, BOOTP, DHCP, IP Routing, Routing protocols
www.infotech.monash.edu
Addressing Issues
• Name to IP address conversion
• /etc/hosts file
– used first
• If unsatisfied, need to find a nameserver
– use /etc/resolv.conf to search find resolver
> [may be running a local nameserver (named)
so this may not be necessary]
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Domain Name Service (DNS)
• Server listens on UDP port 53
• Provides distributed database of names and associated
IP addresses
• Consists of local network-based servers that connect to
authoritative servers if they cannot resolve name
• Local servers cache responses for future use
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Domain Hierarchy
Top-level domain (.) has root servers
• these have only information about top-level domains
– au, .., za, edu, org, com, etc
• Top-level servers have information about their particular
domain
eg…
“org.au” server has all registered names listed
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Name Server software
DNS on UNIX systems use Berkeley Internet Name
Daemon (BIND)
• http://www.isc.org/sw/bind/
• Consists of two parts:
– resolver implements a policy that requests the lookup of a name
– nameserver responds to the request
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Name Server software - Types
BIND usually runs as the process “named”
on systems that provide name service
Categories of name server:
• Primary
–
–
–
–
loads information from disk
has complete information about the domain
always accurate
Authoritative - only one server per domain
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Name Server software - Types
• Secondary
– periodically transfers from primary server - authoritative for their
own domain
• Caching-only
– get answers for all name service queries
from other name servers
– non-authoritative
use second-hand and incomplete DNS data
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New Domain Names must be registered
• ensure appropriate allocation
– Identify organisations and responsible persons (not always
done!)
• create pointers to
– authoritative server
• create DNS entries [primary and secondary]
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Why register domain?
New network setup
• A new organisation will need a domain registered for their
network if they intend to connect to the Internet.
Web-hosting
• Web servers differentiate between hosted sites using different
domain names
– eg, www.netcomp.monash.edu.au is neptune.netcomp.monash.edu.au
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named Configuration
Several files used by the nameserver daemon:
• named.boot
sets general parameters and points to domain database
information (local files or remote servers)
• named.ca
points to the root domain servers
• named.hosts
maps host names to IP addresses
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named Configuration…
• named.rev
reverse domain maps IP addresses to host names
• named.local
used for loopback address resolution
http://www.isc.org/sw/bind/arm94/Bv9ARM.ch03.html
http://www.netadmintools.com/art25.html
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named.boot
;
;
;
;
;
;
;
;
;
;
;
;
;
;
;
;
;
;
;
;
;
Description:
Syntax:
The named.boot file is required to boot a BIND name server.
directory
;[comment]
primary
secondary
cache
slave
forwarders
<directory_name>
;[comment]
domain
host
<directory_name>
<domain> <file>
<domain> [<host> <host>...] <file>
<domain> <file>
<host> [<host> <host>...]
location where domain data files are stored
text following the ';' character is ignored
For a secondary or primary line, the name of the BIND
domain for which the server is a secondary or primary
server. For a cache line, the name of the domain for
which the file, <file>, is a cache.
For a secondary line, the IP address of a primary or
secondary server distributing the database for domain,
<domain>. For a forwarders line, the IP address of a host
to which queries should be forwarded.
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Named.boot continued…
; file
For a secondary line, the name of the file in which the
;
data of domain, <domain>, received from one of the hosts
;
specified can be dumped. For a primary line, the file from
;
which to read the master copy of the domain data. For a
;
cache line, the name of the file in which the cache is
;
stored.
;
Directory
/etc/namedb
;
;secondary
newcontent.net.au 203.24.105.16 db.newcontent
;secondary
maplecorp.com.au 203.24.105.16 db.maplecorp
;secondary
avram.com.au
24.192.21.121 avram.com.au.sec
;
;
Primary 0.0.127.in-addr.arpa named.local
Primary avram.com.au avram.com.au
;
; load the cache data last
Cache
.
named.ca
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named.ca
; BIND data file for initial cache data for root domain servers.
;
.
99999999
IN
NS
ns.nic.ddn.mil.
.
99999999
IN
NS
aos.arl.army.mil.
.
99999999
IN
NS
c.psi.net.
.
99999999
IN
NS
terp.umd.edu.
.
99999999
IN
NS
ns.nasa.gov.
.
99999999
IN
NS
nic.nordu.net.
.
99999999
IN
NS
ns1.isi.edu.
.
99999999
IN
NS
ns.isc.org.
.
99999999
IN
NS
ns.internic.net.
ns.nic.ddn.mil. 99999999
IN
A
192.112.36.4
aos.arl.army.mil. 99999999
IN
A
128.63.4.82
99999999
IN
A
192.5.25.82
c.psi.net.
99999999
IN
A
192.33.4.12
terp.umd.edu.
99999999
IN
A
128.8.10.90
ns.nasa.gov.
99999999
IN
A
128.102.16.10
99999999
IN
A
192.52.195.10
nic.nordu.net.
99999999
IN
A
192.36.148.17
ns1.isi.edu.
99999999
IN
A
128.9.0.107
ns.isc.org.
99999999
IN
A
192.5.5.241
ns.internic.net. 99999999
IN
A
198.41.0.4
; BIND
; BIND
; BIND
; BIND
; BIND
;
;
;
;
BIND
BIND
BIND
BIND
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named.local
;
; BIND data file for local loopback interface.
;
@
IN
SOA
broncho.ct.monash.edu.au.
postmaster.broncho.ct.monash.edu.au. (
1
; Serial
3600
; Refresh
300
; Retry
3600000 ; Expire
3600 ) ; Minimum
IN
NS
broncho.ct.monash.edu.au.
1
IN
PTR
localhost.
b
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Subnet masks
• Sub network masks provide an alternative to class-based
IP addressing
• An administrator will have the responsibility for setting
subnet masks for routers and workstations
• May be used to identify IP addresses that are local to a
subnetwork
• 255.255.255.0 is the usual value
(same as Class C addressing)
http://antionline.com/archive/index.php/t-125580.html
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BOOTP
• Used to allocate an IP address to a particular computer
• BOOTP host resides on the local network. Network node
needing address allocation requests by broadcasting a
bootp packet
• receives a response with address and other associated
information [eg, nameserver address, gateway address]
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Dynamic Host Configuration Protocol
• Also used to allocate IP address
• Network node needing address allocation requests using
DHCP broadcast
• Receives a response with address and other associated
information [eg, nameserver, gateway, time server, etc]
from DHCP servers
• Has provision for reuse of addresses from a pool of
dynamic (ie reusable) IP addresses
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Windows Internet Name Server WINS
• Microsoft technique for locating other windows machines
• A WINS server receives nameservice requests from windows
workstations
• WINS resolution is necessary in larger IP networks.
• As well as IP, also resolve NetBIOS addresses
• May be carried out using DCHP or DNS.
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Routers
• Packets must be forwarded between networks
• Routers can link dissimilar LANs
– ie LANs using dissimilar physical/datalink transport
• Routing decisions are made at network layer based on IP
address whereas bridging (switching) forwards packets
based on datalink address (eg ethernet)
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Routers connecting between remote sites
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Network Routing
• To ensure the appropriate routing of the traffic, routers
implement either proprietary routing methods (eg
netBIOS) or one of the standard routing protocols (eg
Internet Protocol).
• IP-routing is the common form used in TCP/IP networks
and is based upon a table look-up. Routing is done by a
device which could either be a computer or a dedicated
hardware unit providing the interface between subnetworks of a larger internetwork.
Required Reading:
http://www.networkcomputing.com/netdesign/1122ipr.html
(please follow the links therein under table of contents to all six
parts of this primer on IP routing).
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IP Routing
Eg the following network, has 3 subnetworks which would
be identified in the networks file as:
IP address
Name
223.1.2
development
223.1.3
accounting
223.1.4
factory
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IP Routing…
all machines have /etc/hosts file
with the entries shown below
IP address
Name
223.1.1.1
alpha
223.1.2.2
epsilon
223.1.3.2
iota
223.1.1.1
devnetrouter, delta
223.1.2.1
accnetrouter
223.1.3.1
facnetrouter
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Each machine maintains a route table
For machine ALPHA
Target
Network
Network Name
Local?
Router IP
Interface
223.1.1
Development
Direct
-
1
223.1.2
Accounting
Indirect
223.1.1.1
1
223.1.3
Factory
Indirect
223.1.1.1
1
Local?
Router IP
Interface
For machine DELTA
Target
Network
Network Name
223.1.1
Development
Direct
-
1
223.1.2
Accounting
Direct
-
2
223.1.3
Factory
Direct
-
3
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Route table (cont’d)
IP address
223.1.1.2
223.1.2.2
223.1.3.2
223.1.1.1
223.1.2.1
223.1.3.1
Name
alpha
epsilon
iota
devnetrouter delta
accnetrouter
facnetrouter
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Route table (cont’d)
• It is essential that each router operates using the same
routing table, but how can multiple copies of a common
table be kept up to date?
• This requires a separate exchange of messages between
neighbouring routers so that each can advise others
when something changes…
• These are called “Routing Protocols”
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Routing protocols
Routing Information Protocol (RIP)
• Regularly broadcasts entire routing table to all neighbours
• Best route is then chosen based on network path that has
minimum number of hops
Inter-Gateway Routing Protocol (IGRP)
• Chooses network path based on:
–
–
–
–
measured round-trip delay for transfer of data, or
smallest bandwidth, or
channel capacity or
the reliability of the path
Required Reading
http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/igrp.htm
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Link State Routing Protocols
Open Shortest Path First (OSPF)
• routing information flooded
IS-IS INTERMEDIATE SYSTEM - INTERMEDIATE SYSTEM
• For large collections of independent networks
• Allows internal routing method to be hidden from internet
• Border Gateway Protocol (BGP)
• Netware Link Services Protocol (NLSP)
Required Reading:
http://www.ciscopress.com/articles/article.asp?p=26850&rl=1
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End…
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