From 2e253a83bebb889b4669081aefc002fb29f37441 Mon Sep 17 00:00:00 2001
From: Marek Vavrusa <marek@vavrusa.com>
Date: Tue, 19 Jul 2016 21:36:20 -0700
Subject: [PATCH] daemon: lower minimum allowed edns bufsize to 512
there are cases where switches or middle-boxes
block DNS/UDP answers >512 octets completely,
this gives user an option to mitigate that.
however, there are authoritatives serving
large answers that don't support TCP, so it's
a compromise as always
---
daemon/README.rst | 6 +++---
daemon/bindings.c | 4 ++--
lib/defines.h | 2 +-
3 files changed, 6 insertions(+), 6 deletions(-)
diff --git a/daemon/README.rst b/daemon/README.rst
index 8f9c8af93..7a892cc04 100644
--- a/daemon/README.rst
+++ b/daemon/README.rst
@@ -542,14 +542,14 @@ For when listening on ``localhost`` just doesn't cut it.
.. function:: net.bufsize([udp_bufsize])
- Get/set maximum EDNS payload available. Default is 1452 (the maximum unfragmented datagram size).
- You cannot set less than 1220 (minimum size for DNSSEC) or more than 65535 octets.
+ Get/set maximum EDNS payload available. Default is 1452, increase it in cases when authoritatives send large payloads over UDP and don't support TCP.
+ You cannot set less than 512 (512 is DNS packet size without EDNS, 1220 is minimum size for DNSSEC) or more than 65535 octets.
Example output:
.. code-block:: lua
- > net.bufsize(4096)
+ > net.bufsize 4096
> net.bufsize()
4096
diff --git a/daemon/bindings.c b/daemon/bindings.c
index 761cc6589..3653f5d39 100644
--- a/daemon/bindings.c
+++ b/daemon/bindings.c
@@ -301,8 +301,8 @@ static int net_bufsize(lua_State *L)
return 1;
}
int bufsize = lua_tointeger(L, 1);
- if (bufsize < KNOT_EDNS_MIN_DNSSEC_PAYLOAD || bufsize > UINT16_MAX) {
- format_error(L, "bufsize must be within <1220, 65535>");
+ if (bufsize < 512 || bufsize > UINT16_MAX) {
+ format_error(L, "bufsize must be within <512, 65535>");
lua_error(L);
}
knot_edns_set_payload(opt_rr, (uint16_t) bufsize);
diff --git a/lib/defines.h b/lib/defines.h
index 0acc273a1..eed0e416c 100644
--- a/lib/defines.h
+++ b/lib/defines.h
@@ -62,7 +62,7 @@ static inline int __attribute__((__cold__)) kr_error(int x) {
*/
#define KR_DNS_PORT 53
#define KR_EDNS_VERSION 0
-#define KR_EDNS_PAYLOAD 4096 /* Default UDP payload (max unfragmented UDP is 1452B) */
+#define KR_EDNS_PAYLOAD 1452 /* Default UDP payload (max unfragmented UDP is 1452B) */
/*
* Address sanitizer hints.
--
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