NetScaler

Cache EDNS0 client subnet data when the NetScaler appliance is in proxy mode

September 21, 2020

Contributed by:

S C

In NetScaler Proxy mode, if a back-end server that supports EDNS0 Client Subnet (ECS) sends a response containing the ECS option, the NetScaler appliance forwards the response as-is to the client and stores it in the cache, along with the client subnet information. Further DNS requests that are from the same subnet of the same domain, and for which the server would send the same response, are then served from the cache instead of being directed to the server.

Note:

ECS caching is disabled by default. You have to enable caching of EDNS0 client-subnet data in the associated DNS profile.
The number of subnets that you can cache for a domain is limited to the available subnet IDs, that is, 1270 in the NetScaler appliance. Optionally, you can set the limit to a lower number (minimum value: 1 ipv4/ipv6).

Enable caching of ECS responses by using the CLI

At the command prompt, type:

set dns profile <dnsProfileName> -cacheECSSubnet ( ENABLED | DISABLED )

Limit the number of subnets that can be cached per domain by using the CLI

At the command prompt, type:

set dns profile <dnsProfileName> -maxSubnetsPerDomain <positive_integer>

Example:

localized image

In the example shown in the above figure, the client at IP address 2.2.2.2 sends a query for www.example.com to the DNS resolver, and the DNS resolver sends the following response:

www.example.com IN A, IP is 2.2.2.11, and ECS 2.2.2.0/24/24

At this point, the response and the client-subnet identifier (2.2.2.0/24) are cached. Further requests from the same subnet and domain will be served from the cache.

For example, if the client’s IP address is 2.2.2.100 and the query is for www.example.com, the query is served from the cache instead of being sent to the backend server.

The official version of this content is in English. Some of the Citrix documentation content is machine translated for your convenience only. Citrix has no control over machine-translated content, which may contain errors, inaccuracies or unsuitable language. No warranty of any kind, either expressed or implied, is made as to the accuracy, reliability, suitability, or correctness of any translations made from the English original into any other language, or that your Citrix product or service conforms to any machine translated content, and any warranty provided under the applicable end user license agreement or terms of service, or any other agreement with Citrix, that the product or service conforms with any documentation shall not apply to the extent that such documentation has been machine translated. Citrix will not be held responsible for any damage or issues that may arise from using machine-translated content.

Cache EDNS0 client subnet data when the NetScaler appliance is in proxy mode

September 21, 2020

Contributed by:

S C

September 21, 2020

Contributed by:

S C

Cache EDNS0 client subnet data when the NetScaler appliance is in proxy mode

Enable caching of ECS responses by using the CLI

Limit the number of subnets that can be cached per domain by using the CLI

In this article