CISCO-GSLB-DNS-MIB

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.