resolve: change DNS_PACKET_UNICAST_SIZE_LARGE_MAX to 1232 (#27171)

The old common default was 4096, until 2020 on which all DNS servers (verified
on BIND9, NSD, Unbound, dnsmasq) switched to 1232 as an agreed max size [1].

[1] https://www.dnsflagday.net/2020/#message-size-considerations

diff --git a/src/resolve/resolved-dns-packet.h b/src/resolve/resolved-dns-packet.h
index 505e3e7ba940731fb7b4351c8726d9107ad072ed..e4d3e94c68379e6e39da92e1ab43d2a0de71fcae 100644 (file)
--- a/src/resolve/resolved-dns-packet.h
+++ b/src/resolve/resolved-dns-packet.h
@@ -55,8 +55,8 @@ assert_cc(sizeof(DnsPacketHeader) == 12);
 /* RFC 1035 say 512 is the maximum, for classic unicast DNS */
 #define DNS_PACKET_UNICAST_SIZE_MAX 512u
 
-/* With EDNS0 we can use larger packets, default to 4096, which is what is commonly used */
-#define DNS_PACKET_UNICAST_SIZE_LARGE_MAX 4096u
+/* With EDNS0 we can use larger packets, default to 1232, which is what is commonly used */
+#define DNS_PACKET_UNICAST_SIZE_LARGE_MAX 1232u
 
 struct DnsPacket {
         unsigned n_ref;