tcp/ip administration

www.infotech.monash.edu

TCP/IP Administration

IP addresses & Names

DNS, BOOTP, DHCP, IP Routing, Routing protocols


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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]


3

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


5

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-authoritativeuse 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.capoints to the root domain servers

• named.hostsmaps host names to IP addresses


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named Configuration…

• named.revreverse domain maps IP addresses to host names

• named.localused for loopback address resolution

http://www.netadmintools.com/art25.html

http://www.isc.org/sw/bind/arm94/Bv9ARM.ch03.html


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named.boot;; Description: The named.boot file is required to boot a BIND name server.;; Syntax: directory <directory_name>; ;[comment]; primary <domain> <file>; secondary <domain> [<host> <host>...] <file>; cache <domain> <file>; slave; forwarders <host> [<host> <host>...];; <directory_name> location where domain data files are stored; ;[comment] text following the ';' character is ignored; domain 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.; host 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.localPrimary avram.com.au avram.com.au;; load the cache data lastCache . 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 ; BINDaos.arl.army.mil. 99999999 IN A 128.63.4.82 ; BIND 99999999 IN A 192.5.25.82c.psi.net. 99999999 IN A 192.33.4.12 ; BINDterp.umd.edu. 99999999 IN A 128.8.10.90 ; BINDns.nasa.gov. 99999999 IN A 128.102.16.10 ; BIND 99999999 IN A 192.52.195.10nic.nordu.net. 99999999 IN A 192.36.148.17 ; BINDns1.isi.edu. 99999999 IN A 128.9.0.107 ; BINDns.isc.org. 99999999 IN A 192.5.5.241 ; BINDns.internic.net. 99999999 IN A 198.41.0.4 ; 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 sub-networks 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…

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

all machines have /etc/hosts filewith the entries shown below


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Each machine maintains a route table

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

For machine ALPHA

Target Network

Network Name

Local? Router IP Interface

223.1.1 Development Direct - 1

223.1.2 Accounting Direct - 2

223.1.3 Factory Direct - 3

For machine DELTA


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IP address Name223.1.1.2 alpha223.1.2.2 epsilon223.1.3.2 iota223.1.1.1 devnetrouter delta223.1.2.1 accnetrouter223.1.3.1 facnetrouter

Route table (cont’d)


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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 hopsInter-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 Readinghttp://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


End…

tcp/ip administration

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