The MIB defines objects for status and statistics
information of DNS related operations of
Global Server Load Balancer(GSLB).  The MIB defines
objects for global statistical information like DNS
queries received, DNS responses sent, etc.  Further it
defines objects for answer, answer group, domain list,
source address list, proximity rule and DNS rule
statistics.  It also defines related notifications.

Acronyms and terminology:

DNS                   : Domain Name System (RFC1035)

D-proxy               : Local DNS name server of the
                       client.

Answer                : Refers to resources to which the GSLB
                       device resolves DNS requests that it
                       receives.

                       There are three possible types
                       of answers:

                       Virtual IP (VIP) :
                           Addresses associated with a
                           server load balancer device,
                           a web server, a cache, etc.

                       Name Server (NS) : 
                           Configured DNS name server on the
                           network that can answer queries
                           that the GSLB device can not
                           resolve.

                       Content Routing Agent (CRA) :
                           A device which uses a resolution
                           process called DNS race to send
                           identical and simultaneous
                           responses back to a client D-proxy
                           for proximity determination.

Answer group          : A logical grouping of answers.  It is a
                       set of virtual IP address (VIP), name
                       server (NS), or content routing agent
                       (CRA) addresses from which an
                       individual answer is selected and used
                       to reply to a content request.  Answers
                       are grouped together as resource pools.
                       The GSLB device, using one of a number
                       of available balance methods, can
                       choose the most appropriate resource
                       to serve each user request from the
                       answers in an answer group.

Balance method        : A balance method is an algorithm for
                       selecting the best server for
                       replying to a DNS query. 

Domain list           : A collection of domain names for
                       Internet or intranet resources that
                       have been delegated to the GSLB device
                       for DNS query responses.  Domain lists
                       either contain complete domain names
                       or regular expression that specifies a
                       pattern by which the GSLB device
                       matches incoming DNS requests.

Source address list   : A collection of IP addresses or address
                       blocks meant to hold information about
                       known D-proxies.  This information is
                       used by the GSLB device while answering
                       DNS queries.

DNS rule              : A rule which controls the operation of
                       GSLB device.  It identifies the actions
                       to be performed by the GSLB device when
                       it receives a DNS request from a known
                       source (a member of a source address
                       list) for a known domain (a member of
                       a domain list) by specifying which
                       response (answer) is to be given to
                       the requesting D-proxy and how that
                       answer is chosen.

Proximity             : Refers to the distance or delay, in
                       terms of network topology and not
                       geographic distance, between the
                       requesting client D-proxy and the
                       resources corresponding to that
                       request.

Proximity probing     : To respond to DNS requests with the
                       most proximate answers, the GSLB
                       device communicates with a probing
                       device located in each proximity zone
                       to gather round-trip time (RTT) metric
                       information measured between the
                       requesting client D-proxy and the
                       zone.  The GSLB device then directs
                       client requests to an available
                       resource with the lowest RTT value.

Proximity subsystem   : Component within the GSLB device
                       responsible for proximity
                       determination.

Clause                : A clause specifies that a particular
                       answer group serve the request and a
                       specific balance method be used to
                       select the best resource from that
                       answer group.

Boomerang server      : A method of proximity routing used by
                       GSLB device with CRAs.  It is also
                       known as DNS race.

                       The boomerang method is based on the
                       concept that instantaneous proximity
                       can be determined if a CRA within each
                       data center sends a DNS A-record
                       (IP address) at the exact same time
                       to the requesting D-proxy.  This gives
                       all CRAs a chance at resolving a
                       client request and allows for
                       proximity to be determined without
                       probing the client D-proxy.
                       Whichever DNS A-record is received
                       first by the D-proxy is, by default,
                       considered to be the most proximate.

                       For the GSLB device to initiate a DNS
                       race, it needs to establish the
                       following two pieces of information
                       for each CRA:
                       (a) The delay between the GSLB device
                           and each of the CRAs in each data
                           center.  With this data, the GSLB
                           device computes how long to delay
                           the race from each data center,
                           so that each CRA starts the race
                           simultaneously.
                       (b) The online status of the CRAs.
                           With this data, the GSLB device
                           knows not to forward requests to
                           any CRA that is not responding.

                       The boomerang server on the GSLB device
                       gathers this information by sending
                       keepalive messages at predetermined
                       intervals.  The boomerang server uses
                       this data, along with the IP addresses
                       of the CRAs, to request the exact start
                       time of the DNS race.  If the CRA
                       response is to be accepted by the
                       D-proxy, each CRA must spoof the IP
                       address of the GSLB device to which
                       the original DNS request was sent.