doc: document ldpd's "ttl-security" commands

Signed-off-by: Renato Westphal <renato@opensourcerouting.org>

diff --git a/doc/user/ldpd.rst b/doc/user/ldpd.rst
index 149e851891be8d4728c14ed3e3eb6e39b9bf4c05..682443a456676469a723934e97811dc60984d6d1 100644 (file)
--- a/doc/user/ldpd.rst
+++ b/doc/user/ldpd.rst
@@ -128,6 +128,21 @@ LDP Configuration
    the IPv4 or IPv6 transport-address used by the LDP protocol to talk on this
    interface.
 
+.. clicmd:: ttl-security disable
+
+   Located under the LDP address-family node, use this command to disable the
+   GTSM procedures described in RFC 6720 (for the IPv4 address-family) and
+   RFC 7552 (for the IPv6 address-family).
+
+   Since GTSM is mandatory for LDPv6, the only effect of disabling GTSM for the
+   IPv6 address-family is that *ldpd* will not discard packets with a hop limit
+   below 255. This may be necessary to interoperate with older implementations.
+   Outgoing packets will still be sent using a hop limit of 255 for maximum
+   compatibility.
+
+   If GTSM is enabled, multi-hop neighbors should have either GTSM disabled
+   individually or configured with an appropriate ttl-security hops distance.
+
 .. clicmd:: neighbor A.B.C.D password PASSWORD
 
    The following command located under MPLS router node configures the router
@@ -143,6 +158,19 @@ LDP Configuration
    this time of non response, the LDP established session will be considered as
    set to down. By default, no holdtime is configured for the LDP devices.
 
+.. clicmd:: neighbor A.B.C.D ttl-security disable
+
+   Located under the MPLS LDP node, use this command to override the global
+   configuration and enable/disable GTSM for the specified neighbor.
+
+.. clicmd:: neighbor A.B.C.D ttl-security hops (1-254)
+
+   Located under the MPLS LDP node, use this command to set the maximum number
+   of hops the specified neighbor may be away. When GTSM is enabled for this
+   neighbor, incoming packets are required to have a TTL/hop limit of 256
+   minus this value, ensuring they have not passed through more than the
+   expected number of hops. The default value is 1.
+
 .. clicmd:: discovery hello holdtime HOLDTIME
 
 .. clicmd:: discovery hello interval INTERVAL