1 files changed, 18 insertions, 0 deletions

diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index fbe427a6580c..a0e134dd2523 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -1086,6 +1086,24 @@ accept_dad - INTEGER
         2: Enable DAD, and disable IPv6 operation if MAC-based duplicate
            link-local address has been found.
 
+force_tllao - BOOLEAN
+        Enable sending the target link-layer address option even when
+        responding to a unicast neighbor solicitation.
+        Default: FALSE
+
+        Quoting from RFC 2461, section 4.4, Target link-layer address:
+
+        "The option MUST be included for multicast solicitations in order to
+        avoid infinite Neighbor Solicitation "recursion" when the peer node
+        does not have a cache entry to return a Neighbor Advertisements
+        message.  When responding to unicast solicitations, the option can be
+        omitted since the sender of the solicitation has the correct link-
+        layer address; otherwise it would not have be able to send the unicast
+        solicitation in the first place. However, including the link-layer
+        address in this case adds little overhead and eliminates a potential
+        race condition where the sender deletes the cached link-layer address
+        prior to receiving a response to a previous solicitation."
+
 icmp/*:
 ratelimit - INTEGER
         Limit the maximal rates for sending ICMPv6 packets.