Global Server Load Balancing

Drop Packet

BIG-IP DNS drops the DNS request.

Use

Drop Packet

for the

Alternate

load balancing method when you want to ensure that BIG-IP DNS does not offer in a response a virtual server that is potentially unavailable.

No

Yes

Yes

Fallback IP

BIG-IP DNS distributes DNS name resolution requests to a virtual server that you specify. This virtual server is not monitored for availability.

Use

Fallback IP

for the fallback load balancing method when you want BIG-IP DNS to return a disaster recovery site when the preferred and alternate load balancing methods do not return an available virtual server.

No

No

Yes

Global Availability

BIG-IP DNS distributes DNS name resolution requests to the first available virtual server in a pool. BIG-IP DNS starts at the top of a manually configured list of virtual servers and sends requests to the first available virtual server in the list. Only when the virtual server becomes unavailable does BIG-IP DNS send requests to the next virtual server in the list. Over time, the first virtual server in the list receives the most requests and the last virtual server in the list receives the least requests.

Use

Global Availability

when you have specific virtual servers that you want to handle most of the requests.

Yes

Yes

Yes

None

BIG-IP DNS distributes DNS name resolution requests skipping either the next available pool in a multiple pool configuration or the current load balancing method. If all pools are unavailable, BIG-IP DNS returns an aggregate of the IP addresses of all the virtual servers in the pool using BIND.

Use

None

for the alternate and fallback methods when you want to limit each pool to a single load balancing method. If the preferred load balancing method fails, BIG-IP DNS offers the next pool in a load balancing response.

No

Yes

Yes

Ratio

BIG-IP DNS distributes DNS name resolution requests among the virtual servers in a pool or among pools in a multiple pool configuration using

weighted round robin

, a load balancing pattern in which requests are distributed among several resources based on a priority level or weight assigned to each resource.

Use

Ratio

when you want to send twice as many connections to a fast server and half as many connections to a slow server.

Yes

Yes

Yes

Return to DNS

BIG-IP DNS immediately distributes DNS name resolution requests to an LDNS for resolution.

Use

Return to DNS

when you want to temporarily remove a pool from service. You can also use

Return to DNS

when you want to limit a pool in a single pool configuration to only one or two load balancing attempts.

No

Yes

Yes

Round Robin

BIG-IP DNS distributes DNS name resolution requests in a circular and sequential pattern among the virtual servers in a pool. Over time each virtual server receives an equal number of requests.

Use

Round Robin

when you want to distribute requests equally among all virtual servers in a pool.

Yes

Yes

Yes

Static Persist

BIG-IP DNS distributes DNS name resolution requests to the first available virtual server in a pool using the persist mask with the source IP address of the LDNS and a hash algorithm to determine the order of the virtual servers in the list. This hash algorithm orders the virtual servers in the list differently for each LDNS that is passing traffic to the system taking into account the specified CIDR of the LDNS. Each LDNS (and thus each client) generally resolves to the same virtual server; however, when the selected virtual server becomes unavailable, BIG-IP DNS sends requests to another virtual server until the original virtual server becomes available. Then BIG-IP DNS again resolves requests to that virtual server.

Use

Static Persist

when you want requests from a specific LDNS to resolve to a specific virtual server.

No

Yes

Yes

Topology

BIG-IP DNS distributes DNS name resolution requests using proximity-based load balancing. BIG-IP DNS determines the proximity of the resource by comparing location information derived from the DNS message to the topology records in a topology statement you have configured.

Use

Topology

when you want to send requests from a client in a particular geographic region to a data center or server located in that region.

Yes

Yes

Yes