From eb92fb32b746f2104b0f370b5b295bb8dd4bd5e5 Mon Sep 17 00:00:00 2001 From: Simon Kelley Date: Tue, 7 Mar 2023 22:07:46 +0000 Subject: [PATCH] Set the default maximum DNS UDP packet size to 1232. Upstream: https://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=commit;h=eb92fb32b746f2104b0f370b5b295bb8dd4bd5e5 http://www.dnsflagday.net/2020/ refers. Thanks to Xiang Li for the prompt. [dalang@gmx.at: backport from upstream] Signed-off-by: Daniel Lang --- CHANGELOG | 9 ++++++++ man/dnsmasq.8 | 3 ++- src/config.h | 2 +- 3 files changed, 12 insertions(+), 2 deletions(-) diff --git a/CHANGELOG b/CHANGELOG index 3af20cf..52d8678 100644 --- a/CHANGELOG +++ b/CHANGELOG @@ -1,3 +1,12 @@ version 2.90 +version 2.90 + 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= 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= 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 */ -- 2.20.1