BROCADE IP PRIMER

Enter: Global Server Load Balancing (GSLB)A zone describes the name servers that serve the zone, the mail servers thatserver the zone, and the individual host resolutions. This is collected in what isreferred to as the DNS zone file or zone database.The A RecordThe A record is the line in the zone file that matches an individual name to anIP address. The “A” is for “address.” In our example for “www.brocade.com,”the DNS servers that are authoritative for “brocade.com” would have a zonefile for “brocade.com.” In this zone file would be an A record that might looksomething like this:www IN A 63.236.63.244The “IN” is an outdated keyword standing for “Internet” (as opposed to localname resolution). The “A” specifies that this is an A record. The “www” is theindividual host name. Now, how do we know that this is resolving “www.brocade.com”and not some other “www?” Because this line is in the“brocade.com” zone file. Finally, the IP address that it should resolve to is alsolisted.Additional Information About DNSFor more information about DNS, you might look to:• RFC 1034 and RFC 1035; these describe DNS structure and implementation;they can be read online at http://www.ietf.org/• The Internet Assigned Numbers Authority (IANA) has several pages dealingwith DNS and TLDs; they can be reached at http://www.iana.org/• ISC (http://www.isc.org/) — they are the keepers of the BIND DNS serversoftware; they also have many documents and information relating toDNS• DNS and BIND by Cricket Liu and Paul Albitz (Published by O'Reilly); todate, this is considered the authority on DNSEnter: Global Server Load Balancing (GSLB)GSLB acts as a DNS proxy. We mentioned that before. But what good does thatdo me? Let's say that you have three geographically-diverse sites. All threesites serve the same web content. You want clients to use all three sites. “Noproblem,” you say, “I'll just use DNS round-robin.”DNS round-robin is when you use the same A record to resolve several IPaddresses. Say, for example, that www.something.com resolved to 1.2.3.4,2.3.4.5, and 3.4.5.6. Now, someone doing a lookup using the host ornslookup command is going to see all three IP addresses returned. A client tryingto connect to the site will simply take the first IP address it sees. Most DNSservers, by default, will rotate which IP address is first. For example, for thefirst person to request “www.something.com,” they may see “1.2.3.4, 2.3.4.5,3.4.5.6.” The next person to request “www.something.com” might see“2.3.4.5, 3.4.5.6, 1.2.3.4.” You see where this is going? The next person toBrocade IP Primer 391