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TASK-91082: Changing dnsbuf documentation
Signed-off-by: Doug Koerich <[email protected]>
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‎content/momentum/3/3-reference/3-reference-modules-dnsbuf.md‎

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---
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lastUpdated: "03/26/2020"
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lastUpdated: "09/30/2025"
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title: "dnsbuf – Dynamically Set the DNS UDP Buffer Size"
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description: "Configuration Change This feature is available as beta in Momentum 3 6 5 Momentum does not manipulate the size of UDP sockets it creates and uses for DNS queries instead it will use the default sizes configured by the Operating System This can create problems for clients with too many..."
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---
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<a name="idp19364064"></a>
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**Configuration Change. ** This feature is available as beta in Momentum 3.6.5.
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**Configuration Change.** This feature is available as beta in Momentum 3.6.5.
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> **NOTE: This feature was DEPRECATED in Momentum 4.8. Please refer to the [updated](/momentum/4/modules/dnsbuf-new) module for changes in the functionality.**
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Momentum does not manipulate the size of UDP sockets it creates and uses for DNS queries; instead, it will use the default sizes configured by the Operating System. This can create problems for clients with too many domains (e.g., tens of thousands) in the system. Responses may be dropped, causing unnecessary DNS failures and retries, thus further increasing the DNS query volume. The `dnsbuf` module enables the client to manipulate the DNS buffer sizes on demand, on the fly.
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DNS AAAA Queries: 0
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DNS MX Queries: 908388
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Pending DNS Queries: 311
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```
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```

‎content/momentum/4/4-console-commands.md‎

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| [dns_cache refcnts](/momentum/4/console-commands/dns-cache) – Show the references in the DNS cache | 4.0 |   | dns |
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| [dns_cache stats](/momentum/4/console-commands/dns-cache) – Show summary stats for the DNS cache | 4.0 |   | dns |
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| [dns_cache submit](/momentum/4/console-commands/dns-cache) – Submit a DNS query | 4.0 |   | dns |
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| [dnsbuf interval](/momentum/4/modules/dnsbuf#modules.dnsbuf.console) – Change how often setsockopt() operations are performed | 4.2 | dnsbuf | module |
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| [dnsbuf rcvbuf_size](/momentum/4/modules/dnsbuf#modules.dnsbuf.console) – Change the rcvbuf_size value on the fly | 4.2 | dnsbuf | module |
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| [dnsbuf sndbuf_size](/momentum/4/modules/dnsbuf#modules.dnsbuf.console) – Change the sndbuf_size value on the fly | 4.2 | dnsbuf | module |
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| [dnsbuf verify](/momentum/4/modules/dnsbuf#modules.dnsbuf.console) – Query active sockets for current buffer sizes and report the results | 4.2 | dnsbuf | module |
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| [domain all](/momentum/4/console-commands/domain-all) – Show statistics for all domains | 4.0 |   | stats |
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| [domain](/momentum/4/console-commands/domain) – Show domain statistics | 4.0 |   | stats |
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| [ds_core flush cache_name](/momentum/4/modules/ds-core#modules.ds_core.console) – Flush a specific cache | 4.0 | ds_core | module |

‎content/momentum/4/modules/dnsbuf-new.md‎

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---
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lastUpdated: "09/30/2020"
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title: "dnsbuf – Configure the DNS UDP Buffer Sizes"
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description: "Configuration Change This feature is available in Momentum 4 8 and later"
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---
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<a name="idp21140416"></a>
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**Configuration Change.** This feature is available in Momentum 4.8 and later.
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Momentum does not manipulate the size of UDP sockets it creates and uses for DNS queries; instead, it will use the default sizes configured by the Operating System. This can create problems for clients with too many domains (e.g., tens of thousands) in the system. Responses may be dropped, causing unnecessary DNS failures and retries, thus further increasing the DNS query volume. The `dnsbuf` module enables the client to configure the DNS buffer sizes at the service startup.
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### <a name="modules.dnsbuf.configuration"></a> Configuration
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The `dnsbuf` module is configured as follows:
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<a name="example.dnsbuf"></a>
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```
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dnsbuf {
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sndbuf_size = "65536" # Default value is 131072
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rcvbuf_size = "65536" # Default value is 131072
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}
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```
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<dl class="variablelist">
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<dt>sndbuf_size</dt>
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<dd>
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The SO_SNDBUF value is set to this value for all UDP DNS sockets. Minimum value is 1024\. Note that in Linux the value in the kernel is automatically doubled; e.g., when a value of 65536 is configured in the module, the kernel will implement a buffer size of 131072.
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</dd>
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<dt>rcvbuf_size</dt>
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<dd>
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The SO_RCVBUF value is set to this value for all UDP DNS sockets. Minimum value is 1024\. Note that in Linux the value in the kernel is automatically doubled; e.g., when a value of 65536 is configured in the module, the kernel will actually implement a buffer size of 131072.
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</dd>
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</dl>
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### <a name="modules.dnsbuf.subtleties"></a> Subtleties
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* Changes in the values require a service restart to take effect. They are *not* applied in a configuration reload.
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* The buffer cannot be set beyond the **sysctl**-defined maximums in Linux:
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```
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net.core.rmem_max
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net.core.wmem_max
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```
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Note that those values are the post-doubled values; e.g., if `net.core.wmem_max` is set to 65536, the maximum value that will work in the `dnsbuf` module is `sndbuf_max` = 32768.
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### <a name="modules.dnsbuf.dropped"></a> Determining that DNS Responses are Being Dropped
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To determine whether the DNS responses are being dropped because the DNS UDP socket buffer is full, look for a corresponding increase in the "Pending DNS Queries" statistic from Momentum and the UDP packet errors from netstat, e.g.:
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```
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while sleep 1; do (netstat --udp -s | grep error; echo summary |
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/opt/msys/ecelerity/bin/ec_console | grep DNS); echo; done
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```
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The following is an example in which Momentum started with ~30,000 unresolvable domains in the queue. Notice that the "packet receive errors" number has increased, and there are a high number of pending DNS queries.
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```
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1559857 packet receive errors
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DNS A Queries: 924801
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DNS AAAA Queries: 0
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DNS MX Queries: 907577
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Pending DNS Queries: 312
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1559857 packet receive errors
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DNS A Queries: 924803
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DNS AAAA Queries: 0
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DNS MX Queries: 907849
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Pending DNS Queries: 43
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1560125 packet receive errors
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DNS A Queries: 924803
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DNS AAAA Queries: 0
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DNS MX Queries: 908388
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Pending DNS Queries: 311
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```

‎content/momentum/4/modules/dnsbuf.md‎

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---
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lastUpdated: "03/26/2020"
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lastUpdated: "09/30/2020"
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title: "dnsbuf – Dynamically Set the DNS UDP Buffer Size"
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description: "Configuration Change This feature is available in Momentum 4 2 and later Momentum does not manipulate the size of UDP sockets it creates and uses for DNS queries instead it will use the default sizes configured by the Operating System This can create problems for clients with too many domains..."
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---
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<a name="idp21140416"></a>
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**Configuration Change. ** This feature is available in Momentum 4.2 and later.
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**Configuration Change.** This feature is available from Momentum 4.2 through 4.7.
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> **NOTE: This feature was DEPRECATED in Momentum 4.8. Please refer to the [updated](/momentum/4/modules/dnsbuf-new) module for changes in the functionality.**
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Momentum does not manipulate the size of UDP sockets it creates and uses for DNS queries; instead, it will use the default sizes configured by the Operating System. This can create problems for clients with too many domains (e.g., tens of thousands) in the system. Responses may be dropped, causing unnecessary DNS failures and retries, thus further increasing the DNS query volume. The `dnsbuf` module enables the client to manipulate the DNS buffer sizes on demand, on the fly.
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DNS AAAA Queries: 0
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DNS MX Queries: 908388
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Pending DNS Queries: 311
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```
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```

‎content/momentum/4/modules/index.md‎

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| [custom_logger](/momentum/4/modules/custom-logger) | User-defined Logging |
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| [dane](/momentum/4/modules/dane) | DANE related DNS Lookups and TLS Verifications |
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| [delay_dsn](/momentum/4/modules/delay-dsn) | Delay DSN Generation |
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| [dnsbuf](/momentum/4/modules/dnsbuf) | Dynamically Set the DNS UDP Buffer Size |
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| [dnsbuf](/momentum/4/modules/dnsbuf-new) | Configure the DNS UDP Buffer Sizes |
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| [domainkeys](/momentum/4/modules/domainkeys) | Yahoo! DomainKeys |
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| [ds_core](/momentum/4/modules/ds-core) | Datasource Query Core |
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| [EC_logger](/momentum/4/modules/ec-logger) | Momentum-Style Logging |

‎content/momentum/4/modules/summary-all-modules.md‎

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| [dk_validate](/momentum/4/modules/domainkeys) | 4.0 | Validate inbound mail checking domain keys signatures |   |   |  ✓ |   |
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| [dkim_sign](/momentum/4/modules/opendkim) | 4.0 | Attach DKIM signatures to outbound mail |   |   |  ✓ |   |
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| [dkim_validate](/momentum/4/modules/opendkim) | 4.0 | Validate inbound mail checking DKIM signatures |   |   |  ✓ |   |
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| [“dnsbuf – Dynamically Set the DNS UDP Buffer Size”](/momentum/4/modules/dnsbuf) | 4.2 | Manipulate DNS buffer sizes on demand |   |   |   |   |
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| [“dnsbuf – Configure the DNS UDP Buffer Sizes”](/momentum/4/modules/dnsbuf-new) | 4.8 | Set UDP buffer sizes for DNS |   |   |   | [“dnsbuf – Dynamically Set the DNS UDP Buffer Size”](/momentum/4/modules/dnsbuf) **(DEPRECATED)** |
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| [“ds_core - Datasource Query Core”](/momentum/4/modules/ds-core) (*singleton*) | 4.0 | Provide modular data access and caching for use by other modules |  ✓ |   |   |   |
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| [“EC_logger – Momentum-Style Logging”](/momentum/4/modules/ec-logger) | 4.0 | Log the status of messages |   |   |   |   |
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| [“eleven – Eleven eXpurgate Content Scanning”](/momentum/4/modules/eleven) (*singleton*) | 4.0 | This module implements the eleven spam filter and categorization service |   |   |  ✓ |   |

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