bgp: T3967: add support for conditional advertisement

The BGP conditional advertisement feature uses the non-exist-map or the
exist-map and the advertise-map keywords of the neighbor advertise-map command
in order to track routes by the route prefix.

non-exist-map
=============
* If a route prefix is not present in the output of non-exist-map command, then
  advertise the route specified by the advertise-map command.

* If a route prefix is present in the output of non-exist-map command, then do
  not advertise the route specified by the addvertise-map command.

exist-map
=========
* If a route prefix is present in the output of exist-map command, then
  advertise the route specified by the advertise-map command.

* If a route prefix is not present in the output of exist-map command, then do
  not advertise the route specified by the advertise-map command.

This feature is useful when some prefixes are advertised to one of its peers
only if the information from the other peer is not present (due to failure in
peering session or partial reachability etc).

The conditional BGP announcements are sent in addition to the normal
announcements that a BGP router sends to its peer.

CLI nodes can be found under:
* set protocols bgp neighbor <ip> address-family <afi> conditional-advertisement
* set protocols bgp peer-group <p> address-family <afi> conditional-advertisement

1 files changed, 22 insertions, 0 deletions

diff --git a/src/conf_mode/protocols_bgp.py b/src/conf_mode/protocols_bgp.py
index 03fb17ba7..d8704727c 100755
--- a/src/conf_mode/protocols_bgp.py
+++ b/src/conf_mode/protocols_bgp.py
@@ -183,6 +183,28 @@ def verify(bgp):
                     raise ConfigError(f'Neighbor "{peer}" cannot have both ipv6-unicast and ipv6-labeled-unicast configured at the same time!')
 
                 afi_config = peer_config['address_family'][afi]
+
+                if 'conditionally_advertise' in afi_config:
+                    if 'advertise_map' not in afi_config['conditionally_advertise']:
+                        raise ConfigError('Must speficy advertise-map when conditionally-advertise is in use!')
+                    # Verify advertise-map (which is a route-map) exists
+                    verify_route_map(afi_config['conditionally_advertise']['advertise_map'], bgp)
+
+                    if ('exist_map' not in afi_config['conditionally_advertise'] and
+                        'non_exist_map' not in afi_config['conditionally_advertise']):
+                        raise ConfigError('Must either speficy exist-map or non-exist-map when ' \
+                                          'conditionally-advertise is in use!')
+
+                    if {'exist_map', 'non_exist_map'} <= set(afi_config['conditionally_advertise']):
+                        raise ConfigError('Can not specify both exist-map and non-exist-map for ' \
+                                          'conditionally-advertise!')
+
+                    if 'exist_map' in afi_config['conditionally_advertise']:
+                        verify_route_map(afi_config['conditionally_advertise']['exist_map'], bgp)
+
+                    if 'non_exist_map' in afi_config['conditionally_advertise']:
+                        verify_route_map(afi_config['conditionally_advertise']['non_exist_map'], bgp)
+
                 # Validate if configured Prefix list exists
                 if 'prefix_list' in afi_config:
                     for tmp in ['import', 'export']: