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Set the default maximum DNS UDP packet size to 1232.

Browse Source 
http://www.dnsflagday.net/2020/ refers.

Thanks to Xiang Li for the prompt.
This commit is contained in:
Simon Kelley
2023-03-07 22:07:46 +00:00
parent 9a698434dd
commit eb92fb32b7
3 changed files with 11 additions and 3 deletions
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9
CHANGELOG
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@@ -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

3
man/dnsmasq.8
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@@ -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

2
src/config.h
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@@ -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 */