2/26/2003Lecture 4

Computer System Administration

Lecture 4Networking Startup/DNS

2/26/2003Lecture 4

Networking Initialization: IRIX

● Hostname– /etc/sys_id

● IP Address– /etc/hosts

● nsswitch.conf● Netmask

– /etc/config/ifconfig-1.options● Default route

– /etc/config/static-route.options

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/etc/config/ifconfig-1.options

● Appended to ifconfig command for first interface– netmask 0xffffff00

● 255.255.255.0● /24

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/etc/config/static-route.options

● Script file, multiple routing commands can be added– $ROUTE $QUIET add default 128.213.30.1

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IRIX: Multiple Interfaces

● Hostname-INTERFACE– /etc/hosts

● irix-1-ec0.sysadmin.cs.rpi.edu– /etc/config/ifconfig-#.options

● Netmasks, etc.. for additional controllers– /etc/config/static-route.options

● Add additional $ROUTE lines

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Solaris: Networking Startup

● Hostname– /etc/hostname.INTERFACE

● Machine hostname from primary interface● IP Address

– /etc/hosts● /etc/nsswitch.conf

● Netmask– /etc/netmasks

● Default Route– /etc/defaultrouter

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Solaris: Multiple Interfaces

● Hostnames– /etc/hostname.INTERFACE

● Only primary interface sets global hostname● IP Address

– /etc/hosts● Netmask

– /etc/netmasks● Static routes

– Create your own startup script using route(1)

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FreeBSD: Networking Startup

● All in /etc/rc.conf● Hostname

– hostname=”hostname”● IPAddress/Netmask

– ifconfig_INTERFACE=”inet address netmask netmask”

● Default Route– defaultrouter=”address”

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FreeBSD: Multiple Interfaces

● All in /etc/rc.conf– No need to reset hostname

● IP addresses– Additional ifconfig_INTERFACE lines

● Static routes– static_routes=”name1 name2...”– route_name1=”route(8) args”

● route add ${route_name1}

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DNS: Client Configuration

● /etc/nsswitch.conf– IRIX/Solaris/FreeBSD5+/Many Linux Distributions– hosts:

● files– /etc/hosts

● dns– DNS

● nis– YP/NIS

– Man(1)-page!

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DNS: Resolver

● /etc/resolv.conf– domain

● Default appended to end of most requests.– search

● List of possible extensions to requests– Mutually exclusive– nameserver

● Can be listed multiple times● Adds additional servers to the ones queried

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Libresolv and state

● resolver library is stateless/unshared– Failed nameservers keep being tried, with delay

● Name Service Caching– Keeps state of servers– Solaris

● nscd– Name Service Cache Daemon

– Irix● nsd

– Name Service Daemon

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DNS: 2 Databases

● Name to address (Forward)– Registrars

● Verisign, EDUCause, etc...– edu/com/net/org/biz/cc/...

● Address to name (reverse)– NICs

● ARIN/APNIC/RIPE– in-addr.arpa.

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DNS Hierarchies (forward)

.

EduCom Arpa

RPI

CS

MIT Microsoft In-addr

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IP Delegations (reverse)ICANN

IANA

ARIN APNIC RIPE

AOL

You

RPICS

Registrars

Verisign Educause

RPICS

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Forward

● Forward– Delegated on “.” boundaries– Bottom up

● edu is the most broad● then rpi is more specific● then cs● Etc.

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vs. Reverse

● Reverse– Delegated on “.” boundaries– Top down.

● 128.213 is the most broad (classes!)● 30 is more specific● 2 is a given host.

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IP Classes

● Class based IP routing– A

● 127 class A addresses, each address has 16.7million IPs– /8– All addresses begin (bitwise) 0

– B● ~50,000 class B addresses, each address has 65536 Ips

– /16– All Addresses begin (bitwise) 10

– C● Many, 256 Ips, /24, begin “110”

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Classless Routing

● Poor utilization of IP addresses– Class A addresses largely wasted.

● Allows for almost arbitrary sized networks– 24.a.b.c no longer 1 network

● 24.5.7.x/24● 24.6.x.y/16● 24.8.0.0-24.9.255.255/17● 128.213.30.16-128.213.30.31/28

● Much more load on routers

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DNS: Start of Authority

● SOA– Required to delegate a domain– Fields to specify maintainership of a domain

● Authoritative server● Authoritative email (in DNS format)● Serial number● Refresh● Retry● Expire (TTL)● Minimum

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DNS: Other records

● NS: NameServer– IN NS name

● A: Address– IN NS IP_Address

● MX: Mail Exchange– IN MX priority name

● TXT: Text– IN TXT “data”

● RP: Responsible Person, points to a TXT

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DNS: Other Records

● CNAME (alias)– IN CNAME name– Cannot be combined with types other than A and PTR

● PTR (Pointer) (reverse DNS)– IN PTR name

● AAAA/A6– 2 types of IPv6 address

● AAAA: raw, undelegated. A6: delegated

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Reverse Lookup

● Reverse (literally) lookup– IP Address must be reversed so it too is in bottom-up

order.– Name-to-address:

● monica.cs.rpi.edu 128.213.7.2– Address-to-name:

● 2.7.213.128.in-addr.arpa monica.cs.rpi.edu

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DNS: Forward Example@ IN SOA turing.cs.rpi.edu. labstaff.cs.rpi.edu. (

200302253 ;Serial86400

;Refresh3600 ;Retry604800 ;Expire

(TTL)86400 )

;Minimumlabstaff IN TXT “Department of Computer Science”

IN NS turing.cs.rpi.edu.IN NS stumble.cs.rpi.edu.IN NS netserv1.its.rpi.edu.

turing IN A 128.213.1.1IN MX 1 mumble.cs.rpi.edu.

stumble IN A 128.213.8.7IN MX 1 mumble.cs.rpi.edu.

netserv1.its.rpi.edu. IN A 128.113.1.5www IN CNAME stumble

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DNS: Reverse Example@ IN SOA turing.cs.rpi.edu. labstaff.cs.rpi.edu. (

20030221386400360060480086400 )

IN NS turing.cs.rpi.edu.IN NS stumble.cs.rpi.edu.IN NS netserv1.its.rpi.edu.

2.7 IN PTR monica.cs.rpi.edu.1.1 IN PTR turing.cs.rpi.edu.18.30 IN PTR irix-1.sysadmin.cs.rpi.edu.

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DNS: Forward Delegationdelegate IN NS their.name.server.

IN NS their-secondary.name.server.their.name.server IN A addresstheir-secondary.name.server IN A address

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DNS: Reverse Delegation24 IN NS their.name.server.

;must be in fwdIN NS their-

secondary.name.server. ;must be in fwd

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DNS: Classless Reverse Delegation

● Delegating reverse DNS when not on “.” boundaries– RFC 2317– Clever and painfull use of CNAMEs(aliases)– Create new level of DNS in reverse and alias all

reverse IPs to that.

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DNS: Classless Reverse Delegation, Delegator

; using delegation of 128.213.30.16/28 as an example16/28 IN NS group-1-dns.sysadmin.cs.rpi.edu.

IN NS group-1-secondary-dns.sysadmin.cs.rpi.edu.16 IN CNAME 16.16/28.30.213.128.in-addr.arpa.17 IN CNAME 17.16/28.30.213.128.in-addr.arpa.18 IN CNAME 18.16/28.30.213.128.in-addr.arpa.19 IN CNAME 19.16/28.30.213.128.in-addr.arpa.20 IN CNAME 20.16/28.30.213.128.in-addr.arpa.21 IN CNAME 21.16/28.30.213.128.in-addr.arpa.

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DNS: Classless Reverse Delegation, Delegate-ed

$ORIGIN 16/28.30.213.128.in-addr.arpa16 IN PTR net.group1.sysadmin.cs.rpi.edu.17 IN PTR router.group1.sysadmin.cs.rpi.edu.18 IN PTR irix.group1.sysadmin.cs.rpi.edu.19 IN PTR solaris.group1.sysadmin.cs.rpi.edu.20 IN PTR freebsd.group1.sysadmin.cs.rpi.edu.

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DNS: Server Configuration

● Type of server– Master– Slave– Cache

● Zone Config files– Forward– Reverse– hints

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named.confacl transferers {

128.213.0.0/16; 128.113.0.0/16; 1.2.3.4; };acl local {128.213.0.0/16; 128.113.0.0/16};acl evil {2.3.4.5;};options {

directory “/etc/namedb”;allow-transfer { transferers; };allow-recursion { local; };blackhole { evil; };recursion no;

};zone “vassar.edu” {

type slave;file “slave/vassar.edu”;masters { 143.229.1.6; };

};

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Named.conf (cont)Zone “.” { /* sets the default $ORIGIN */

type hint;file “named.root”; /*file of root “.” name servers.

};zone “213.128.in-addr.arpa” { type master; file “master/cs.rpi.edu.rev”; also-notify { 128.213.8.7; 128.113.1.3; }};zone “cs.rpi.edu” {

type master;file “master/cs.rpi.edu”;also-notify { 128.213.8.7; 128.113.1.3; }

};

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named/bind operations

● $ORIGIN– Changes suffix appended to all unqualified names

● $GENERATE– Used to make series of hosts– Forward

● $GENERATE 100-200 d11-$.dyn IN A 128.213.11.$– Reverse

● $GENERATE 100-200 $.11 IN PTR d11-$.cs.rpi.edu.

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Name-Server Packages● Solaris

– bind8● SUNWcsu

– Core System Utilities– Already installed

– Bind9● http://www.sunfreeware.com/programlistsparc9.html#bind9

● SGI/Irix– Bind8 included– Bind9

● http://www.sunfreeware.com/programlistsparc9.html#bind9

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Name Server Packages(cont)

● FreeBSD– Bind8: Included– Bind9

● pkg_add -r bind9● Remember to make sure it starts automatically!

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Group Names

● foo.group-name.sysadmin.cs.rpi.edu● Existing names will be going away

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Next Lecutre

● NIS!