Basic Server Load Balancing Concept

1) User enters www.example.com in their browser. Hostname sent to DNS for resolution

2) DNS resolves www.example.com to the Virtual IP address (VIP) of 10.10.10.10.

3) Client sends request to VIP.

4) Array proxies request to selected real service.

5) Further requests from the client may be sent to the same or a different real service, depending on persistency configuration.

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IPV4 and IPV6 Subnet Size Reference Table

IPV4 SUBNETTING TABLES

Network Bits Subnet Mask Number of Hosts
/1 128.0.0.0 2147483646
/2 192.0.0.0 1073741822
/3 224.0.0.0 536870910
/4 240.0.0.0 268435454
/6 252.0.0.0 67108862
/7 254.0.0.0 33554430
/8 255.0.0.0 16777214
/9 255.128.0.0 8388606
/10 255.192.0.0 4194302
/11 255.224.0.0 2097150
/12 255.240.0.0 1048574
/13 255.248.0.0 524286
/14 255.252.0.0 262142
/15 255.254.0.0 131070
/16 255.255.0.0 65534
/17 255.255.128.0 32766
/18 255.255.192.0 16382
/19 255.255.224.0 8190
/20 255.255.240.0 4094
/21 255.255.248.0 2046
/22 255.255.252.0 1022
/23 255.255.254.0 510
/24 255.255.255.0 254
/25 255.255.255.128 126
/26 255.255.255.192 62
/27 255.255.255.224 30
/28 255.255.255.240 14
/29 255.255.255.248 6
/30 255.255.255.252 2

IPV6 SUBNETTING TABLES Continue reading

How to do DNS lookup using Dig Command

Dig command is a command line tool use for querying DNS nameservers for information about host addresses, mail exchanges, nameservers, and related information. This tool is available on any Linux (unix) or Mac OS X operating system.

Example of using Dig Command

munkwais-MacBook-Pro:~ munkwai$ dig www.google.com

; <<>> DiG 9.8.3-P1 <<>> www.google.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 32350
;; flags: qr rd ra; QUERY: 1, ANSWER: 5, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;www.google.com. IN A

;; ANSWER SECTION:
www.google.com. 299 IN A 173.194.126.80
www.google.com. 299 IN A 173.194.126.81
www.google.com. 299 IN A 173.194.126.83
www.google.com. 299 IN A 173.194.126.82
www.google.com. 299 IN A 173.194.126.84

;; Query time: 44 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Thu Apr 16 04:29:00 2015
;; MSG SIZE rcvd: 112

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