Computer System Administration

Lecture 4 Networking Startup/DNS Computer System Administration

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

/etc/config/ifconfig-1.options • Appended to ifconfig command for first interface • netmask 0xffffff00 • 255.255.255.0 • /24

/etc/config/static-route.options • Script file, multiple routing commands can be added • $ROUTE $QUIET add default 128.213.30.1

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

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

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)

FreeBSD: Networking Startup • All in /etc/rc.conf • Hostname • hostname=”hostname” • IPAddress/Netmask • ifconfig_INTERFACE=”inet address netmask netmask” • Default Route • defaultrouter=”address”

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}

DNS: Client Configuration • /etc/nsswitch.conf • IRIX/Solaris/FreeBSD5+/Many Linux Distributions • hosts: • files • /etc/hosts • dns • DNS • nis • YP/NIS • Man(1)-page!

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

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

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.

DNS Hierarchies (forward)

IP Delegations (reverse)

Forward • Forward • Delegated on “.” boundaries • Bottom up • edu is the most broad • then rpi is more specific • then cs • Etc.

vs. Reverse • Reverse • Delegated on “.” boundaries • Top down. • 128.213 is the most broad (classes!) • 30 is more specific • 2 is a given host.

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”

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

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

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

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

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

DNS: Forward Example @ IN SOA turing.cs.rpi.edu. labstaff.cs.rpi.edu. ( 200302253 ;Serial 86400 ;Refresh 3600 ;Retry 604800 ;Expire (TTL) 86400 ) ;Minimum labstaff 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 128.213.1.1 IN MX 1 mumble.cs.rpi.edu. stumble IN A 128.213.8.7 IN MX 1 mumble.cs.rpi.edu. netserv1.its.rpi.edu. IN A 128.113.1.5 www IN CNAME stumble

DNS: Reverse Example @ IN SOA turing.cs.rpi.edu. labstaff.cs.rpi.edu. ( 200302213 86400 3600 604800 86400 ) 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.

DNS: Forward Delegation delegate IN NS their.name.server. IN NS their-secondary.name.server. their.name.server IN A address their-secondary.name.server IN A address

DNS: Reverse Delegation 24 IN NS their.name.server. ;must be in fwd IN NS their-secondary.name.server. ;must be in fwd

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.

DNS: Classless Reverse Delegation, Delegator ; using delegation of 128.213.30.16/28 as an example 16/28 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.

DNS: Classless Reverse Delegation, Delegate-ed $ORIGIN 16/28.30.213.128.in-addr.arpa 16 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.

DNS: Server Configuration • Type of server • Master • Slave • Cache • Zone Config files • Forward • Reverse • hints

named.conf acl 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; }; };

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; } };

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.

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

Name Server Packages(cont) • FreeBSD • Bind8: Included • Bind9 • pkg_add -r bind9 • Remember to make sure it starts automatically!

Group Names • foo.group-name.sysadmin.cs.rpi.edu • Existing names will be going away

Next Lecutre • NIS!

Computer System Administration