DNS stands for “Domain Name Service”. It is the mechanism in which the internet is able to map a name (eg http://www.sgasoftware.com) to an IP address (eg 12.34.56.78).
A bit on IP Addresses and Routing
www.google.com
to 72.14.204.99
. c:\>tracert www.google.com
Tracing route to www.l.google.com [72.14.204.99]
over a maximum of 30 hops:
1 <1 ms <1 ms <1 ms 192.168.0.1 (our office router/gateway))
2 1 ms <1 ms <1 ms 10.1.10.1 (our cable modem (another router/gateway)
3 15 ms 13 ms 12 ms 96.179.208.1
4 9 ms 9 ms 10 ms ge-2-20-ur01.blairsville.pa.pitt.comcast.net [68.86.146.165]
5 14 ms 10 ms 9 ms te-9-1-ur01.indiana.pa.pitt.comcast.net [68.86.100.178]
6 10 ms 55 ms 30 ms te-9-3-ur01.punxy.pa.pitt.comcast.net [68.87.173.81]
7 12 ms 18 ms 19 ms te-9-1-ur01.ruralvalley.pa.pitt.comcast.net [68.86.100.122]
8 21 ms 63 ms 53 ms te-6-3-ar01.pittsburgh.pa.pitt.comcast.net [68.87.173.73]
9 28 ms 29 ms 27 ms te-3-1-0-0-cr01.chicago.il.ibone.comcast.net [68.86.90.181]
10 25 ms 28 ms 25 ms pos-1-6-0-0-pe01.350ecermak.il.ibone.comcast.net [68.86.87.130]
11 43 ms 44 ms 44 ms as15169-1.350ecermak.il.ibone.comcast.net [75.149.230.198]
12 48 ms 52 ms 58 ms 209.85.254.130
13 37 ms 39 ms 39 ms 209.85.248.222
14 36 ms 43 ms 41 ms 66.249.94.46
15 42 ms 39 ms 39 ms iad04s01-in-f99.1e100.net [72.14.204.99]
Trace complete.
Why does this matter?
11000000.10101000.00000000.00000001
, humans find it more convenient to look at it like 192.168.0.1
. However, that is still a far cry from a human readable name like mail.domain.com
.Common Types of DNS Records
www.appcove.com. 86400 IN CNAME appcove.com.
appcove.com. 86400 IN MX 40 APPCOVE.COM.S9B2.PSMTP.com.
appcove.com. 86400 IN MX 10 APPCOVE.COM.S9A1.PSMTP.com.
appcove.com. 86400 IN MX 20 APPCOVE.COM.S9A2.PSMTP.com.
appcove.com. 86400 IN MX 30 APPCOVE.COM.S9B1.PSMTP.com.
appcove.com. 57957 IN NS ns.rackspace.com.
appcove.com. 57957 IN NS ns2.rackspace.com.
appcove.com. 86400 IN TXT "v=spf1 include:fogcreek.com include:aspmx.googlemail.com ip4:207.126.144.0/20 ip4:64.18.0.0/20 ip4:74.125.148.0/22 ~all"
DNS Propagation
a.root-servers.net. 117655 IN A 198.41.0.4
a.root-servers.net. 196594 IN AAAA 2001:503:ba3e::2:30
b.root-servers.net. 113829 IN A 192.228.79.201
c.root-servers.net. 120655 IN A 192.33.4.12
d.root-servers.net. 113757 IN A 128.8.10.90
e.root-servers.net. 115554 IN A 192.203.230.10
f.root-servers.net. 121256 IN A 192.5.5.241
f.root-servers.net. 280321 IN AAAA 2001:500:2f::f
g.root-servers.net. 113755 IN A 192.112.36.4
h.root-servers.net. 116456 IN A 128.63.2.53
h.root-servers.net. 206320 IN AAAA 2001:500:1::803f:235
i.root-servers.net. 115856 IN A 192.36.148.17
i.root-servers.net. 337685 IN AAAA 2001:7fe::53
j.root-servers.net. 119155 IN A 192.58.128.30
d.gtld-servers.net. 16131 IN A 192.31.80.30
g.gtld-servers.net. 74653 IN A 192.42.93.30
f.gtld-servers.net. 111162 IN A 192.35.51.30
c.gtld-servers.net. 33590 IN A 192.26.92.30
j.gtld-servers.net. 171076 IN A 192.48.79.30
a.gtld-servers.net. 2665 IN A 192.5.6.30
a.gtld-servers.net. 8352 IN AAAA 2001:503:a83e::2:30
i.gtld-servers.net. 78083 IN A 192.43.172.30
k.gtld-servers.net. 14957 IN A 192.52.178.30
b.gtld-servers.net. 127812 IN A 192.33.14.30
b.gtld-servers.net. 168301 IN AAAA 2001:503:231d::2:30
e.gtld-servers.net. 29652 IN A 192.12.94.30
h.gtld-servers.net. 47519 IN A 192.54.112.30
l.gtld-servers.net. 41990 IN A 192.41.162.30
m.gtld-servers.net. 42456 IN A 192.55.83.30
appcove.com. 172800 IN NS ns2.rackspace.com.
appcove.com. 172800 IN NS ns.rackspace.com.
www.appcove.com. 86400 IN CNAME appcove.com.
appcove.com. 86400 IN A 74.205.111.168