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| author | Simon Kelley <simon@thekelleys.org.uk> | 2023-03-07 22:07:46 +0000 |
|---|---|---|
| committer | Simon Kelley <simon@thekelleys.org.uk> | 2023-03-07 22:21:21 +0000 |
| commit | eb92fb32b746f2104b0f370b5b295bb8dd4bd5e5 (patch) | |
| tree | cca6c2faa87c7db4c33e2dbbb97352e03e7ea70a | |
| parent | 9a698434dd9cc0f3abbf98f9b266c491d322d20f (diff) | |
| download | dnsmasq-eb92fb32b746f2104b0f370b5b295bb8dd4bd5e5.tar.gz | |
Set the default maximum DNS UDP packet size to 1232.
http://www.dnsflagday.net/2020/ refers.
Thanks to Xiang Li for the prompt.
| -rw-r--r-- | CHANGELOG | 9 | ||||
| -rw-r--r-- | man/dnsmasq.8 | 3 | ||||
| -rw-r--r-- | src/config.h | 2 |
3 files changed, 11 insertions, 3 deletions
@@ -7,8 +7,15 @@ version 2.90 domain are configured, but no server which is not qualified for a particular domain. Thanks to Daniel Danzberger for spotting this bug. - + Set the default maximum DNS UDP packet sice to 1232. This + has been the recommended value since 2020 because it's the + largest value that avoid fragmentation, and fragmentation + is just not reliable on the modern internet, especially + for IPv6. It's still possible to override this with + --edns-packet-max for special circumstances. + + version 2.89 Fix bug introduced in 2.88 (commit fe91134b) which can result in corruption of the DNS cache internal data structures and diff --git a/man/dnsmasq.8 b/man/dnsmasq.8 index 41e2e04..5acb935 100644 --- a/man/dnsmasq.8 +++ b/man/dnsmasq.8 @@ -183,7 +183,8 @@ to zero completely disables DNS function, leaving only DHCP and/or TFTP. .TP .B \-P, --edns-packet-max=<size> Specify the largest EDNS.0 UDP packet which is supported by the DNS -forwarder. Defaults to 4096, which is the RFC5625-recommended size. +forwarder. Defaults to 1232, which is the recommended size following the +DNS flag day in 2020. Only increase if you know what you are doing. .TP .B \-Q, --query-port=<query_port> Send outbound DNS queries from, and listen for their replies on, the diff --git a/src/config.h b/src/config.h index 1e7b30f..37b374e 100644 --- a/src/config.h +++ b/src/config.h @@ -19,7 +19,7 @@ #define CHILD_LIFETIME 150 /* secs 'till terminated (RFC1035 suggests > 120s) */ #define TCP_MAX_QUERIES 100 /* Maximum number of queries per incoming TCP connection */ #define TCP_BACKLOG 32 /* kernel backlog limit for TCP connections */ -#define EDNS_PKTSZ 4096 /* default max EDNS.0 UDP packet from RFC5625 */ +#define EDNS_PKTSZ 1232 /* default max EDNS.0 UDP packet from from /dnsflagday.net/2020 */ #define SAFE_PKTSZ 1232 /* "go anywhere" UDP packet size, see https://dnsflagday.net/2020/ */ #define KEYBLOCK_LEN 40 /* choose to minimise fragmentation when storing DNSSEC keys */ #define DNSSEC_WORK 50 /* Max number of queries to validate one question */ |