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Add dnsmasq cache dump documentation
Signed-off-by: DL6ER <dl6er@dl6er.de>
This commit is contained in:
DL6ER
@@ -14,7 +14,6 @@
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.md-typeset code,
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198
docs/ftldns/cache_dump.md
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198
docs/ftldns/cache_dump.md
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## Cache dump interpretation
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The `dnsmasq` core embedded into `pihole-FTL` prints a dump of the current cache content into the mail log file (default location `/var/log/pihole.log`) when receiving `SIGUSR1`, e.g. by
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``` bash
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sudo killall -USR1 pihole-FTL
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```
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Such a crash dump looks like
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``` plain
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cache size 10000, 0/20984 cache insertions re-used unexpired cache entries.
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queries forwarded 10247, queries answered locally 14713
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queries for authoritative zones 0
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pool memory in use 22272, max 24048, allocated 480000
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server 127.0.0.1#5353: queries sent 10801, retried or failed 69
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server 192.168.2.1#53: queries sent 388, retried or failed 3
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Host Address Flags Expires
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imap.strato.de 2a01:238:20a:202:54f0::1103 6F Wed Dec 15 20:51:59 2021
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imap.strato.de 81.169.145.103 4F Wed Dec 15 20:51:59 2021
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api.github.com 6F N Wed Dec 15 20:36:02 2021
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www.googleapis.com 2a00:1450:4001:831::200a 6F Wed Dec 15 20:34:35 2021
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www.googleapis.com 2a00:1450:4001:801::200a 6F Wed Dec 15 20:34:35 2021
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www.googleapis.com 2a00:1450:4001:80e::200a 6F Wed Dec 15 20:34:35 2021
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www.googleapis.com 2a00:1450:4001:80f::200a 6F Wed Dec 15 20:34:35 2021
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www.googleapis.com 142.250.185.170 4F Wed Dec 15 20:34:35 2021
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www.googleapis.com 142.250.185.202 4F Wed Dec 15 20:34:35 2021
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www.googleapis.com 142.250.185.234 4F Wed Dec 15 20:34:35 2021
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www.googleapis.com 142.250.181.234 4F Wed Dec 15 20:34:35 2021
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www.googleapis.com 172.217.16.138 4F Wed Dec 15 20:34:35 2021
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www.googleapis.com 142.250.186.42 4F Wed Dec 15 20:34:35 2021
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www.googleapis.com 142.250.186.74 4F Wed Dec 15 20:34:35 2021
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www.googleapis.com 142.250.186.106 4F Wed Dec 15 20:34:35 2021
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www.googleapis.com 142.250.186.138 4F Wed Dec 15 20:34:35 2021
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www.googleapis.com 142.250.186.170 4F Wed Dec 15 20:34:35 2021
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www.googleapis.com 172.217.18.106 4F Wed Dec 15 20:34:35 2021
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www.googleapis.com 142.250.184.202 4F Wed Dec 15 20:34:35 2021
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www.googleapis.com 142.250.184.234 4F Wed Dec 15 20:34:35 2021
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www.googleapis.com 216.58.212.138 4F Wed Dec 15 20:34:35 2021
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www.googleapis.com 142.250.185.74 4F Wed Dec 15 20:34:35 2021
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www.googleapis.com 142.250.185.106 4F Wed Dec 15 20:34:35 2021
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KLA 192.168.2.246 4F D Thu Dec 16 12:49:00 2021
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dominik-desktop 192.168.2.224 4F D Thu Dec 16 18:03:49 2021
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fritz.repeater 192.168.2.3 4FRI H
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lan F D Thu Dec 16 20:08:29 2021
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dominik-laptop.lan 192.168.2.206 4FR D Thu Dec 16 20:07:45 2021
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dominik-laptop.lan 2a02:b30:f0c:cf00::1ac 6FR D Wed Dec 15 21:07:44 2021
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dominik-laptop.lan fd00::1ac 6FR D Wed Dec 15 21:07:44 2021
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Internet-Radio 192.168.2.239 4F D Thu Dec 16 12:54:33 2021
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Internet-Radio.lan 192.168.2.239 4FR D Thu Dec 16 12:54:33 2021
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textsecure-service.whispersyst 13.248.212.111 4F Wed Dec 15 20:32:00 2021
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textsecure-service.whispersyst 76.223.92.165 4F Wed Dec 15 20:32:00 2021
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textsecure-service.whispersyst 6F N Wed Dec 15 20:42:00 2021
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arduino.hosted-by-discourse.co 184.104.202.141 4F Wed Dec 15 20:35:40 2021
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arduino.hosted-by-discourse.co 2001:470:1:9a5::141 6F Wed Dec 15 20:35:40 2021
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posteo.de 185.67.36.168 4F V Wed Dec 15 20:32:59 2021
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posteo.de 2a05:bc0:1000::168:1 6F V Wed Dec 15 20:32:59 2021
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posteo.de 23244 8 256 KF V Wed Dec 15 20:32:59 2021
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posteo.de 53881 8 257 KF V Wed Dec 15 20:32:59 2021
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posteo.de 53881 8 2 SF V Wed Dec 15 20:46:13 2021
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strato.de SF N V Wed Dec 15 20:51:59 2021
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ip6-allnodes ff02::1 6FRI H
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ubuntu.com SF N V Thu Dec 16 08:31:26 2021
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fritz.2400 192.168.2.3 4F I H
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de 57564 8 256 KF V Wed Dec 15 20:32:59 2021
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de 26755 8 257 KF V Wed Dec 15 20:32:59 2021
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de 63015 8 256 KF V Wed Dec 15 20:32:59 2021
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de 26755 8 2 SF V Thu Dec 16 16:38:18 2021
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<Root> 20326 8 257 KF V Thu Dec 16 17:46:14 2021
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<Root> 14748 8 256 KF V Thu Dec 16 17:46:14 2021
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<Root> 20326 8 2 SF I
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i.stack.imgur.com ipv4.imgur.map.fastly.net CF Fri Dec 17 22:10:29 2021
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[...]
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```
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where we stripped lines like `Dec 15 20:32:02 dnsmasq[4177892]:` for the sake of readability. The format is pretty self-explanatory.
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### Cache metrics
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``` plain
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cache size 10000, 0/20984 cache insertions re-used unexpired cache entries.
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```
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tells us that the cache size is 10000 (Pi-hole's default value). None of the 20984 cache insertions had to overwrite still valid cache lines. If this number is zero, your cache was sufficiently large at any time. If this number is notably larger than zero, you should consider increasing the cache size.
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### Query statistics
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``` plain
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queries forwarded 10247, queries answered locally 14713
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queries for authoritative zones 0
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```
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Mostly self-explanatory. Queries answered locally can both be from local configuration, HOSTS files, DHCP leases, or from the local cache. Queries for authoritative zones can only appear when defining an authoritative zone (`dnsmasq` option `auth-server`).
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### Blockdata statistics
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``` plain
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pool memory in use 22272, max 24048, allocated 480000
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```
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Blockdata is used to cache records that do not fit in normal cache records. These are `SRV` targets, and `DNSKEY` and `DS` key data objects. Negative (empty) entries do not occupy blockdata space. Blocks are preallocated to reduce heap fragmentation.
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### Server statistics
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```
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server 127.0.0.1#5353: queries sent 10801, retried or failed 69
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server 192.168.2.1#53: queries sent 388, retried or failed 3
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```
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Self-explanatory: Queries sent, retried, and failed to the individual upstream servers.
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### Cache content
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The first character of the flags describes the query type:
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Character | Record type
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----------|------------
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`4` | `A` (IPv4 address)
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`6` | `AAAA` (IPv6 address)
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`C` | `CNAME`
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`V` | `SRV`
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`S` | `DS`
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`K` | `DNSKEY`
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`(empty)` | something else
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The rest of the flags can be almost any combination of the following bits:
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Bit | Interpretation
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-------|---------------
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`F` | Forward entry (domain-to-address record)
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`R` | Reverse entry (address-to-domain, typically combined with `D` or `H`)
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`I` | Immortal cache entry (no expiry, typically from local configuration)
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`D` | DHCP-provided record
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`N` | Negative record (This record does not exist)
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`X` | NXDOMAIN (No record exists at all for this domain)
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`H` | From HOSTS file (always combined with `I`)
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`V` | DNSSEC verified
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The `V` flag in negative DS records has a different meaning. Only validated `DS` records are every cached, and the `V` bit is used to store information about the presence of an `NS` record for the domain, i.e., if there's a zone cut at that point.
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### Examples
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#### `A` (`DHCP` provided)
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``` plain
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Host Address Flags Expires
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Internet-Radio 192.168.2.239 4F D Thu Dec 16 12:54:33 2021
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Internet-Radio.lan 192.168.2.239 4FR D Thu Dec 16 12:54:33 2021
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```
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Both cache entries describe an IPv4 cache record for a device in the local network. The `Internet-Radio.lan` has an `R` as it is the name to be served for a reverse lookup as it includes the local network domain `lan`.
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#### `DNSKEY/DS`
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``` plain
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Host Address Flags Expires
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de 57564 8 256 KF V Wed Dec 15 20:32:59 2021
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de 26755 8 257 KF V Wed Dec 15 20:32:59 2021
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de 63015 8 256 KF V Wed Dec 15 20:32:59 2021
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de 26755 8 2 SF V Thu Dec 16 16:38:18 2021
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<Root> 20326 8 257 KF V Thu Dec 16 17:46:14 2021
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<Root> 14748 8 256 KF V Thu Dec 16 17:46:14 2021
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<Root> 20326 8 2 SF I
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```
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The first three cache records are `DNSKEY` records (type `K`) of the `de` domain, the fifth and sixth cache records are `DNSKEY` records of the root zone.
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The three numbers in the `address` field correspond to the key tag, the algorithm ID, and the key flags. The fourth and seventh entry corresponds to a `DS` record (type `S`) where the three numbers are the key tag, the used algorithm ID, and the digest.
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Note that `DS` records may have an empty `address` field when they are `NODATA` (flag `N`) like
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```
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Host Address Flags Expires
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hosted-by-discourse.com SF N V Sat Dec 18 11:06:03 2021
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```
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The `DS` of the root zone is marked *immortal* as it is given by the locally defined `trust-anchor`.
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#### `CNAME`
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``` plain
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Host Address Flags Expires
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i.stack.imgur.com ipv4.imgur.map.fastly.net CF Fri Dec 17 22:10:29 2021
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```
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The `address` field corresponds to the `CNAME` target record.
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#### `SRV`
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``` plain
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Host Address Flags Expires
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_sip._tcp.pcscf2.ims.telekom.d 100 10 5062 pspcscfhost2.ims.telekom.de VF Sat Dec 18 13:33:37 2021
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```
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The `address` field lists the priority (`100` in the example), the weight (`10`), and the SRV port (`5062`), followed by the target (`pspcscfhost2.ims.telekom.de`).
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{!abbreviations.md!}
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@@ -112,6 +112,7 @@ nav:
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- 'Compatibility': ftldns/compatibility.md
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- 'Install from source': ftldns/compile.md
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- 'dnsmasq warnings': ftldns/dnsmasq_warn.md
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- 'Cache dump': ftldns/cache_dump.md
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- 'Debugging FTLDNS':
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- 'gdb': ftldns/debugging.md
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- 'valgrind': ftldns/valgrind.md
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