Thread (14 messages) 14 messages, 2 authors, 2026-01-26
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[PATCH net-next v4 5/7] ipv6: Document defaults for max_{dst|hbh}_opts_number sysctls

From: Tom Herbert <hidden>
Date: 2026-01-21 21:49:59
Subsystem: documentation, networking [general], the rest · Maintainers: Jonathan Corbet, "David S. Miller", Eric Dumazet, Jakub Kicinski, Paolo Abeni, Linus Torvalds

In the descriptions of max_dst_opts_number and max_hbh_opts_number
sysctls add text about how a zero setting means that a packet with
any Destination or Hop-by-Hop options is dropped.

Report the defaults for max_dst_opts_number and max_hbh_opts_number
are 2 which means up to two options may be accepted.

Signed-off-by: Tom Herbert <redacted>
---
 Documentation/networking/ip-sysctl.rst | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)
diff --git a/Documentation/networking/ip-sysctl.rst b/Documentation/networking/ip-sysctl.rst
index bc9a01606daf..5051fe653c96 100644
--- a/Documentation/networking/ip-sysctl.rst
+++ b/Documentation/networking/ip-sysctl.rst
@@ -2474,20 +2474,26 @@ mld_qrv - INTEGER
 	Minimum: 1 (as specified by RFC6636 4.5)
 
 max_dst_opts_number - INTEGER
-	Maximum number of non-padding TLVs allowed in a Destination
-	options extension header. If this value is less than zero
-	then unknown options are disallowed and the number of known
-	TLVs allowed is the absolute value of this number.
+        Maximum number of non-padding TLVs allowed in a Destination
+        options extension header. If this value is zero then receive
+        Destination Options processing is disabled in which case packets
+        with the Destination Options extension header are dropped. If
+        this value is less than zero then unknown options are disallowed
+        and the number of known TLVs allowed is the absolute value of
+        this number.
 
-	Default: 8
+        Default: 2
 
 max_hbh_opts_number - INTEGER
 	Maximum number of non-padding TLVs allowed in a Hop-by-Hop
-	options extension header. If this value is less than zero
-	then unknown options are disallowed and the number of known
-	TLVs allowed is the absolute value of this number.
-
-	Default: 8
+	options extension header. If this value is zero then receive
+        Hop-by-Hop Options processing is disabled in which case packets
+        with the Hop-by-Hop Options extension header are dropped.
+        If this value is less than zero then unknown options are disallowed
+        and the number of known TLVs allowed is the absolute value of this
+        number.
+
+        Default: 2
 
 max_dst_opts_length - INTEGER
 	Maximum length allowed for a Destination options extension
-- 
2.43.0
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