bgpd: support TTL-security with iBGP

Traditionally, ttl-security feature has been associated with EBGP
sessions as those identify directly connected external peers. The
GTSM RFC (rfc 5082) does not make any restrictions on type of
peering. In fact, it is beneficial to support ttl-security for both
EBGP and IBGP sessions. Specifically, in data centers, there are
directly connected IBGP peerings that will benefit from the protection
ttl-security provides.

Signed-off-by: Dinesh G Dutt <ddutt@cumulusnetworks.com>
Reviewed-by: Pradosh Mohapatra <pmohapat@cumulusnetworks.com>
[DL: function refactoring split out into previous 2 patches.  changes:
     - bgp_set_socket_ttl(): ret type int -> void
     - is_ebgp_multihop_configured(): stripped peer == NULL check
     - comments/whitespace]
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>

1 files changed, 8 insertions, 0 deletions

diff --git a/doc/bgpd.texi b/doc/bgpd.texi
index 24028d6f..cb9789bd 100644
--- a/doc/bgpd.texi
+++ b/doc/bgpd.texi
@@ -366,6 +366,14 @@ Note that replace-as can only be specified if no-prepend is.
 This command is only allowed for eBGP peers.
 @end deffn
 
+@deffn {BGP} {neighbor @var{peer} ttl-security hops @var{number}} {}
+@deffnx {BGP} {no neighbor @var{peer} ttl-security hops @var{number}} {}
+This command enforces Generalized TTL Security Mechanism (GTSM), as
+specified in RFC 5082. With this command, only neighbors that are the
+specified number of hops away will be allowed to become neighbors. This
+command is mututally exclusive with @command{ebgp-multihop}.
+@end deffn
+
 @node Peer filtering
 @subsection Peer filtering