Size - Max A or AAAA Records Within Size Limit
This module is designed to generate a DNS response that includes as many A or AAAA records as it is possible to fit within the specified packet size limit.
Default size limit is 512 bytes.
In case the AAAA record is requested, the module responds with AAAA records.
Note that the number of records that can fit in a response depends significantly on whether DNS compression is enabled or disabled. By default, compression is enabled but can be changed in the PolarDNS configuration file. Additionally, compression can be enabled or disabled for individual responses using the fc and nc modifiers.
Category: General features
Format
size.<BYTES>.yourdomain.com
Where:
- The
<BYTES>parameter specifies the maximum size limit for the response. If it is not provided, the default limit is set to 512 bytes.
Examples
In this example, we request a DNS response that is limited to 512 bytes in size (the default value):
# dig size.yourdomain.com @127.0.0.1 ; <<>> DiG 9.18.10-2-Debian <<>> size.yourdomain.com @127.0.0.1 ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 10418 ;; flags: qr aa; QUERY: 1, ANSWER: 29, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;size.yourdomain.com. IN A ;; ANSWER SECTION: size.yourdomain.com. 60 IN A 127.0.0.37 size.yourdomain.com. 60 IN A 127.0.0.78 size.yourdomain.com. 60 IN A 127.0.0.175 size.yourdomain.com. 60 IN A 127.0.0.116 size.yourdomain.com. 60 IN A 127.0.0.99 size.yourdomain.com. 60 IN A 127.0.0.132 size.yourdomain.com. 60 IN A 127.0.0.153 size.yourdomain.com. 60 IN A 127.0.0.22 size.yourdomain.com. 60 IN A 127.0.0.150 size.yourdomain.com. 60 IN A 127.0.0.217 size.yourdomain.com. 60 IN A 127.0.0.238 size.yourdomain.com. 60 IN A 127.0.0.161 size.yourdomain.com. 60 IN A 127.0.0.234 size.yourdomain.com. 60 IN A 127.0.0.171 size.yourdomain.com. 60 IN A 127.0.0.132 size.yourdomain.com. 60 IN A 127.0.0.241 size.yourdomain.com. 60 IN A 127.0.0.216 size.yourdomain.com. 60 IN A 127.0.0.197 size.yourdomain.com. 60 IN A 127.0.0.153 size.yourdomain.com. 60 IN A 127.0.0.221 size.yourdomain.com. 60 IN A 127.0.0.70 size.yourdomain.com. 60 IN A 127.0.0.233 size.yourdomain.com. 60 IN A 127.0.0.119 size.yourdomain.com. 60 IN A 127.0.0.193 size.yourdomain.com. 60 IN A 127.0.0.208 size.yourdomain.com. 60 IN A 127.0.0.241 size.yourdomain.com. 60 IN A 127.0.0.15 size.yourdomain.com. 60 IN A 127.0.0.143 size.yourdomain.com. 60 IN A 127.0.0.197 ;; Query time: 7 msec ;; SERVER: 127.0.0.1#53(127.0.0.1) (UDP) ;; WHEN: Thu Jan 16 10:27:35 +04 2025 ;; MSG SIZE rcvd: 501
We can see that 29 (twenty-nine) A records can fit within this size limit. The response size was exactly 501 bytes.
In this example, we request a DNS response that is limited to 256 bytes in size. We also use the nc modifier to instruct PolarDNS to disable DNS compression for this response:
# dig size.256.nc.yourdomain.com @127.0.0.1 ; <<>> DiG 9.18.10-2-Debian <<>> size.256.nc.yourdomain.com @127.0.0.1 ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 16453 ;; flags: qr aa; QUERY: 1, ANSWER: 5, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;size.256.nc.yourdomain.com. IN A ;; ANSWER SECTION: size.256.nc.yourdomain.com. 60 IN A 127.0.0.88 size.256.nc.yourdomain.com. 60 IN A 127.0.0.42 size.256.nc.yourdomain.com. 60 IN A 127.0.0.230 size.256.nc.yourdomain.com. 60 IN A 127.0.0.191 size.256.nc.yourdomain.com. 60 IN A 127.0.0.250 ;; Query time: 3 msec ;; SERVER: 127.0.0.1#53(127.0.0.1) (UDP) ;; WHEN: Thu Jan 16 10:27:36 +04 2025 ;; MSG SIZE rcvd: 254
We can see that with compression disabled, it’s possible to fit 5 (five) A records within the 256-byte limit.
Now, we enable DNS compression (using the fc modifier) and use the same 256-bytes size limit:
# dig size.256.fc.yourdomain.com @127.0.0.1 ; <<>> DiG 9.18.10-2-Debian <<>> size.256.fc.yourdomain.com @127.0.0.1 ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 38113 ;; flags: qr aa; QUERY: 1, ANSWER: 13, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;size.256.fc.yourdomain.com. IN A ;; ANSWER SECTION: size.256.fc.yourdomain.com. 60 IN A 127.0.0.110 size.256.fc.yourdomain.com. 60 IN A 127.0.0.75 size.256.fc.yourdomain.com. 60 IN A 127.0.0.0 size.256.fc.yourdomain.com. 60 IN A 127.0.0.235 size.256.fc.yourdomain.com. 60 IN A 127.0.0.223 size.256.fc.yourdomain.com. 60 IN A 127.0.0.57 size.256.fc.yourdomain.com. 60 IN A 127.0.0.109 size.256.fc.yourdomain.com. 60 IN A 127.0.0.134 size.256.fc.yourdomain.com. 60 IN A 127.0.0.183 size.256.fc.yourdomain.com. 60 IN A 127.0.0.102 size.256.fc.yourdomain.com. 60 IN A 127.0.0.178 size.256.fc.yourdomain.com. 60 IN A 127.0.0.39 size.256.fc.yourdomain.com. 60 IN A 127.0.0.82 ;; Query time: 3 msec ;; SERVER: 127.0.0.1#53(127.0.0.1) (UDP) ;; WHEN: Thu Jan 16 10:27:38 +04 2025 ;; MSG SIZE rcvd: 252
With compression enabled, we can accomodate 13 (thirteen) A records within the same 256-byte limit.
In this example, we query for the AAAA record and specify size limit of 256 bytes:
# dig AAAA size.256.yourdomain.com @127.0.0.1 ; <<>> DiG 9.18.10-2-Debian <<>> AAAA size.256.yourdomain.com @127.0.0.1 ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 50394 ;; flags: qr aa; QUERY: 1, ANSWER: 7, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;size.256.yourdomain.com. IN AAAA ;; ANSWER SECTION: size.256.yourdomain.com. 60 IN AAAA ::cb47 size.256.yourdomain.com. 60 IN AAAA ::635f size.256.yourdomain.com. 60 IN AAAA ::b655 size.256.yourdomain.com. 60 IN AAAA ::b7e6 size.256.yourdomain.com. 60 IN AAAA ::6a5f size.256.yourdomain.com. 60 IN AAAA ::1845 size.256.yourdomain.com. 60 IN AAAA ::8354 ;; Query time: 11 msec ;; SERVER: 127.0.0.1#53(127.0.0.1) (UDP) ;; WHEN: Thu Jan 16 10:31:18 +04 2025 ;; MSG SIZE rcvd: 237
We can see that 7 (seven) AAAA records can fit within this 256-byte limit. This is with compression enabled (default).