BGP conditional advertisement

BGP conditional advertisement allows the router to advertise a route only when certain conditions are met. Multiple conditions can be used together, with conditional route map entries treated as an AND operator, and IPv6 is supported.

Multiple conditions example

In this example, the FortiGate only advertises routes to its neighbor 2.2.2.2 if it learns multiple BGP routes defined in its conditional route map entry. All conditionals must be met.

To configure multiple conditions in BGP conditional advertisements:

1. Configure the IPv4 prefix list:

   config router prefix-list
       edit "281"
           config rule
               edit 1
                   set prefix 172.28.1.0 255.255.255.0
                   unset ge
                   unset le
               next
           end
       next
       edit "282"
           config rule
               edit 1
                   set prefix 172.28.2.0 255.255.255.0
                   unset ge
                   unset le
               next
           end
       next
       edit "222"
           config rule
               edit 1
                   set prefix 172.22.2.0 255.255.255.0
                   unset ge
                   unset le
               next
           end
       next
   end

2. Configure the IPv4 route maps:

   config router route-map
       edit "2814"
           config rule
               edit 1
                   set match-ip-address "281"
               next
           end
       next
       edit "2224"
           config rule
               edit 1
                   set match-ip-address "222"
               next
           end
       next
       edit "2824"
           config rule
               edit 1
                   set match-ip-address "282"
               next
           end
       next
   end

3. Configure the IPv6 prefix list:

   config router prefix-list6
       edit "adv-2226"
           config rule
               edit 1
                   set prefix6 2003:172:22:1::/64
                   unset ge
                   unset le
               next
           end
       next
       edit "list6-1"
           config rule
               edit 1
                   set prefix6 2003:172:28:1::/64
                   unset ge
                   unset le
               next
           end
       next
       edit "list6-2"
           config rule
               edit 1
                   set prefix6 2003:172:28:2::/64
                   unset ge
                   unset le
               next
           end
       next
   end

4. Configure the IPv6 route maps:

   config router route-map
       edit "map-2226"
           config rule
               edit 1
                   set match-ip6-address "adv-2226"
               next
           end
       next
       edit "map-2816"
           config rule
               edit 1
                   set match-ip6-address "list6-1"
               next
           end
       next
       edit "map-2826"
           config rule
               edit 1
                   set match-ip6-address "list6-2"
               next
           end
       next
   end

5. Configure the BGP settings:

   config router bgp
       config neighbor
           edit "2.2.2.2"
               config conditional-advertise
                   edit "2224"
                       set condition-routemap "2814" "2824"
                       set condition-type non-exist
                   next
               end
           next
           edit "2003::2:2:2:2"
               config conditional-advertise6
                   edit "map-2226"
                       set condition-routemap "map-2816" "map-2826"
                   next
               end
               set route-reflector-client6 enable
           next
       end
   end

To verify the IPv4 conditional advertisements:

# get router info bgp neighbors 2.2.2.2
...
  Conditional advertise-map:
        Adv-map 2224root 2814root, cond-state 0-1
                         2824root, cond-state 0-1
...

In this output, the condition is that the routes in route maps 2814 and 2824 do not exist. However, routes for 2814 and 2224 exist, so the conditions are not met.

To verify the IPv6 conditional advertisements:

# get router info6 bgp neighbors 2003::2:2:2:2
...
  Conditional advertise-map:
        Adv-map map-2226root map-2816root, cond-state 1-1
                            map-2826root, cond-state 1-0
...

In this output, the condition is that the routes in route maps map-2816 and map-2826 exist. However, routes for map-2816 exist, but map-2826 does not, so the conditions are not met.

To view the conditional route maps:

# diagnose ip router command show-vrf root show running router bgp
...
 neighbor 2.2.2.2 advertise-map 2224root exist-map 2814root
 neighbor 2.2.2.2 advertise-map 2224root exist-map 2824root
... ...
 !
 address-family ipv6
 neighbor 2003::2:2:2:2 advertise-map map-2226root non-exist-map map-2816root
 neighbor 2003::2:2:2:2 advertise-map map-2226root non-exist-map map-2826root
!

IPv6 example 1

In this example, the FortiGate advertises its local network to the secondary router when the primary router is down. The FortiGate detects the primary router is down in the absence of a learned route.

• When the FortiGate learns route 2003:172:28:1::/64 from the primary router, it does not advertise its local route (2003:172:22:1::/64) to the secondary router.

• When the FortiGate does not learn route 2003:17:28:1::/64 from the primary router, advertises its local route (2003:172:22:1::/64) to the secondary router.

• The BGP conditional advertisement condition is set to be true if the condition route map (2003:172:28:1::/64) is not matched (non-exist).

To configure BGP conditional advertisement with IPv6:

1. Configure the IPv6 prefix lists:

   config router prefix-list6
       edit "adv-222"
           config rule
               edit 1
                   set prefix6 2003:172:22:1::/64
                   unset ge
                   unset le
               next
           end
       next
       edit "lrn-281"
           config rule
               edit 1
                   set prefix6 2003:172:28:1::/64
                   unset ge
                   unset le
               next
           end
       next
   end

2. Configure the route maps:

   config router route-map
       edit "map-221"
           config rule
               edit 1
                   set match-ip6-address "adv-222"
               next
           end
       next
       edit "map-281"
           config rule
               edit 1
                   set match-ip6-address "lrn-281"
               next
           end
       next
   end

3. Configure BGP:

   config router bgp
       set as 65412
       set router-id 1.1.1.1
       set ibgp-multipath enable
       set network-import-check disable
       set graceful-restart enable
       config neighbor
           edit "2003::2:2:2:2"
               set soft-reconfiguration6 enable
               set remote-as 65412
               set update-source "loopback1"
               config conditional-advertise6
                   edit "map-221"
                       set condition-routemap "map-281"
                       set condition-type non-exist
                   next
               end
           next
           edit "2003::3:3:3:3"
               set soft-reconfiguration6 enable
               set remote-as 65412
               set update-source "loopback1"
           next
       end
   end

   In this configuration, if route map map-281 does not exist, then the FortiGate advertises route map map-221 to neighbor 2003::2:2:2:2.

4. Verify the routing table:

   # get router info6 routing-table bgp
   B       2003:172:28:1::/64 [200/0] via 2003::3:3:3:3 (recursive via ****::***:***:****:****, port9), 01:23:45
   B       2003:172:28:2::/64 [200/0] via 2003::3:3:3:3 (recursive via ****::***:***:****:****, port9), 23:09:22

When the FortiGate learns 2003:172:28:1::/64, it will not advertise its local route 2003:172:22:1::/64 to neighbor 2003::2:2:2:2. If the FortiGate has not learned 2003:172:28:1::/64, it will advertise its local route 2003:172:22:1::/64 to neighbor 2003::2:2:2:2.

IPv6 example 2

With the same IPv6 prefix lists and route maps, when the FortiGate does learn 2003:172:28:1::/64, it advertises local route 2003:172:22:1::/64 to the secondary router. The BGP conditional advertisement condition is set to be true if the condition route map is matched (exist).

To configure BGP conditional advertisement with IPv6:

1. Configure BGP:

   config router bgp
       config neighbor
           edit "2003::2:2:2:2"
               config conditional-advertise6
                   edit "map-221"
                       set condition-routemap "map-281"
                       set condition-type exist
                   next
               end
           next
       end
   end

2. Verify the routing table:

   # get router info6 routing-table bgp
   B       2003:172:28:1::/64 [200/0] via 2003::3:3:3:3 (recursive via ****::***:***:****:****, port9), 01:23:45
   B       2003:172:28:2::/64 [200/0] via 2003::3:3:3:3 (recursive via ****::***:***:****:****, port9), 23:09:22

When the FortiGate learns 2003:172:28:1::/64, it will advertise its local route 2003:172:22:1::/64 to neighbor 2003::2:2:2:2. If the FortiGate has not learned route 2003:172:28:1::/64, it will not advertise its local route 2003:172:22:1::/64 to neighbor 2003::2:2:2:2.

BGP conditional advertisements for IPv6 prefix when IPv4 prefix conditions are met and vice-versa

The FortiGate supports conditional advertisement of IPv4 and IPv6 route maps with edit <advertise-routemap> under config conditional-advertise, and supports configuring IPv4 and IPv6 route maps as conditions with the condition-routemap setting.

The FortiGate can cross-check conditions involving IPv4 and IPv6 route maps and perform conditional advertisements accordingly when those conditions are met. The global option, cross-family-conditional-adv in the BGP configuration settings allows this cross-checking to occur.

config router bgp
    set cross-family-conditional-adv {enable | disable}
    config conditional-advertise
        edit <advertise-routemap>
            set advertise-routemap <string>
            set condition-routemap <name1>, <name2>, ...
            set condition-type {exist | non-exist}
        next
    end
end

By default, the cross-family-conditional-adv setting is disabled. When disabled, the FortiGate will only check conditional route maps against the routing information base (RIB) of the IP address family (IPv4 or IPv6) that corresponds to the IP address family of the route map to be advertised conditionally.

For example, for an IPv6 conditional advertisement, if IPv4 conditional route maps have been configured, then the FortiGate will not meet any of these conditions because IPv4 routes will not exist in the IPv6 RIB. The same behavior applies for an IPv4 conditional advertisement, namely, that the FortiGate will not meet any configured IPv6 conditions since these routes will not exist in the IPv4 RIB. If routes do not match a conditional route map, then the condition is considered non-existent.

IPv4 and IPv6 BGP conditional advertisements using advertising and conditional route maps of the same IP address family are already supported in previous versions of FortiOS.

DS-Lite example

In this example, the FortiGate acts as a Dual-Stack Lite (DS-Lite) address family transition router (AFTR) where the customer equipment (CE) network via Router1 uses IPv6 and where Router2 is the internet gateway using IPv4.

The administrator of the AFTR has the following requirements:

• The FortiGate needs to announce IPv4 pools for NAT translation towards the internet gateway only if the IPv6 B4 prefix exists in the routing table.

• The FortiGate needs to advertise the DS-Lite termination IPv6 address towards the CE network only if the IPv4 default route exists on the FortiGate.

The prefixes defined in IPv4 route map 2814 and IPv6 route map map-281 both exist, so the FortiGate advertises the route map prefix in route-map 2224 (172.22.2.0/255.255.255.0) to its BGP neighbor 2.2.2.2.

For IPv6 neighbor 2003::2:2:2:2, the prefixes defined in IPv4 route map 2874 and IPv6 route map map-38 both do not exist, and the condition-type is set to non-exist, so the FortiGate advertises the route map prefix in route map map-222 (2003:172:22:1::/64) to its BGP neighbor 2003::2:2:2:2.

When the global cross-family-conditional-adv enabled, this is the only time the FortiGate will cross-check the address family; otherwise, it only checks the corresponding conditional map and treats the cross-family addresses as non-existent.

To configure the conditional advertisement to BGP neighbor 2.2.2.2 and its conditional route maps:

1. Configure the IPv4 prefix lists:

   config router prefix-list
       edit "281"
           config rule
               edit 1
                   set prefix 172.28.1.0 255.255.255.0
                   unset ge
                   unset le
               next
           end
       next
       edit "222"
           config rule
               edit 1
                   set prefix 172.22.2.0 255.255.255.0
                   unset ge
                   unset le
               next
           end
       next
   end

2. Configure the IPv6 prefix list:

   config router prefix-list6
       edit "list6-1"
           config rule
               edit 1
                   set prefix6 2003:172:28:1::/64
                   unset ge
                   unset le
               next
           end
       next
   end

3. Configure the route maps:

   config router route-map
       edit "2814"
           config rule
               edit 1
                   set match-ip-address "281"
               next
           end
       next
       edit "map-281"
           config rule
               edit 1
                   set match-ip6-address "list6-1"
               next
           end
       next
       edit "2224"
           config rule
               edit 1
                   set match-ip-address "222"
               next
           end
       next
   end

To configure the conditional advertisement to BGP neighbor 2003::2.2.2.2 and its conditional route maps:

1. Configure the IPv4 prefix list:

   config router prefix-list
       edit "287"
           config rule
               edit 1
                   set prefix 172.28.7.0 255.255.255.0
                   unset ge
                   unset le
               next
           end
       next
   end

2. Configure the IPv6 prefix lists:

   config router prefix-list6
       edit "list6-38"
           config rule
               edit 1
                   set prefix6 2003:172:38:1::/64
                   unset ge
                   unset le
               next
           end
       next
       edit "adv-222"
           config rule
               edit 1
                   set prefix6 2003:172:22:1::/64
                   unset ge
                   unset le
               next
           end
       next
   end

3. Configure the route maps:

   config router route-map
       edit "2874"
           config rule
               edit 1
                   set match-ip-address “287”
               next
           end
       next
       edit "map-38"
           config rule
               edit 1
                   set match-ip6-address "list6-38"
               next
           end
       next
       edit "map-222"
           config rule
               edit 1
                   set match-ip6-address "adv-222"
               next
           end
       next
   end

To configure the BGP settings with address family cross-checking:

config router bgp
    set as 65412
    set router-id 1.1.1.1
    set ibgp-multipath enable
    set network-import-check disable
    set cluster-id 1.1.1.1
    set graceful-restart enable
    set cross-family-conditional-adv enable
    config neighbor
        edit "3.3.3.3"
            set activate6 disable
            set capability-graceful-restart enable
            set soft-reconfiguration enable
            set prefix-list-out "local-out"
            set remote-as 65412
            set route-map-out "as-prepend"
            set keep-alive-timer 30
            set holdtime-timer 90
            set update-source "loopback1"
            set route-reflector-client enable
        next
        edit "2.2.2.2"
            set advertisement-interval 5
            set activate6 disable
            set capability-graceful-restart enable
            set soft-reconfiguration enable
            set remote-as 65412
            set keep-alive-timer 34
            set holdtime-timer 90
            set update-source "loopback1"
            config conditional-advertise
                edit "2224"
                    set condition-routemap "2814" "map-281"
                next
            end
            set route-reflector-client enable
        next
        edit "2003::2:2:2:2"
            set advertisement-interval 5
            set activate disable
            set capability-graceful-restart6 enable
            set soft-reconfiguration enable
            set soft-reconfiguration6 enable
            set remote-as 65412
            set keep-alive-timer 30
            set holdtime-timer 90
            set update-source "loopback1"
            config conditional-advertise6
                edit "map-222"
                    set condition-routemap "map-38" "2874"
                    set condition-type non-exist
                next
            end
            set route-reflector-client6 enable
        next
        edit "2003::3:3:3:3"
            set advertisement-interval 5
            set activate disable
            set capability-graceful-restart6 enable
            set soft-reconfiguration6 enable
            set remote-as 65412
            set route-map-in6 "community-del777"
            set keep-alive-timer 30
            set holdtime-timer 90
            set update-source "loopback1"
        next
    end
    config network
        edit 1
            set prefix 172.27.1.0 255.255.255.0
        next
        edit 2
            set prefix 172.27.2.0 255.255.255.0
        next
        edit 3
            set prefix 172.22.2.0 255.255.255.0
        next
    end
    config network6
        edit 1
            set prefix6 2003:172:22:1::/64
        next
    end
end

To verify the BGP status and the BGP routing table for IPv4:

# get router info bgp summary
VRF 0 BGP router identifier 1.1.1.1, local AS number 65412
BGP table version is 2
6 BGP AS-PATH entries
2 BGP community entries

Neighbor   V         AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
2.2.2.2    4      65412     100     148        2    0    0 00:42:22        3
3.3.3.3    4      65412      99      99        2    0    0 00:42:05        6
6.6.6.6    4         20       0       0        0    0    0    never Idle (Admin)
10.100.1.1 4         20     100     107        2    0    0 00:43:43        2
10.100.1.5 4         20      53      57        2    0    0 00:43:42        0

Total number of neighbors 5

Condition route map:
  2814, state 1, use 3
  map-281, state 1, use 3

To verify the BGP status and the BGP routing table for IPv6:

# get router info6 bgp summary
VRF 0 BGP router identifier 1.1.1.1, local AS number 65412
BGP table version is 3
6 BGP AS-PATH entries
2 BGP community entries

Neighbor      V         AS MsgRcvd MsgSent   TblVer  InQ OutQ Up/Down  State/PfxRcd
6.6.6.6       4         20       0       0        0    0    0    never Idle (Admin)
10.100.1.1    4         20     100     108        3    0    0 00:43:51        0
10.100.1.5    4         20      53      57        3    0    0 00:43:50        0
2003::2:2:2:2 4      65412      98     118        3    0    0 00:42:25        1
2003::3:3:3:3 4      65412     102     100        2    0    0 00:42:20        3

Total number of neighbors 5

Condition route map:
  map-38, state 0, use 3
  2874, state 0, use 3

To verify the BGP routing table for IPv4 and confirm the conditional advertisement occurred:

# get router info routing-table bgp
Routing table for VRF=0
B       172.22.2.0/24 [200/0] via 1.1.1.1 (recursive via 172.16.203.1, agg2), 00:00:03, [1/0]
B       172.27.1.0/24 [200/0] via 1.1.1.1 (recursive via 172.16.203.1, agg2), 00:37:30, [1/0]
B       172.27.2.0/24 [200/0] via 1.1.1.1 (recursive via 172.16.203.1, agg2), 00:37:30, [1/0]
B       172.27.5.0/24 [200/0] via 1.1.1.1 (recursive via 172.16.203.1, agg2), 00:37:30, [1/0]
B       172.27.6.0/24 [200/0] via 1.1.1.1 (recursive via 172.16.203.1, agg2), 00:37:30, [1/0]
B       172.27.7.0/24 [200/0] via 1.1.1.1 (recursive via 172.16.203.1, agg2), 00:37:30, [1/0]
B       172.27.8.0/24 [200/0] via 1.1.1.1 (recursive via 172.16.203.1, agg2), 00:37:30, [1/0]
B       172.29.1.0/24 [200/0] via 1.1.1.1 (recursive via 172.16.203.1, agg2), 00:37:30, [1/0]
B       172.29.2.0/24 [200/0] via 1.1.1.1 (recursive via 172.16.203.1, agg2), 00:37:30, [1/0]

To verify the BGP routing table for IPv6 and confirm the conditional advertisement occurred:

# get router info6 routing-table bgp
Routing table for VRF=0
B       2003:172:22:1::/64 [200/0] via 2003::1:1:1:1 (recursive via 2003:172:16:203::1, agg2), 00:00:01, [1024/0]
B       2003:172:28:1::/64 [200/0] via 2003::3:3:3:3 (recursive via fe80::a5b:eff:feeb:ca45, port1), 00:37:59, [1024/0]
B       2003:172:28:2::/64 [200/0] via 2003::3:3:3:3 (recursive via fe80::a5b:eff:feeb:ca45, port1), 00:37:59, [1024/0]

Behavior when address family cross-checking is disabled

Using a similar BGP configuration with cross-family-conditional-adv disabled, note the following behavior based on the condition type.

When the condition type is set to exist:

config router bgp
	set cross-family-conditional-adv disable
	config neighbor
        edit "2.2.2.2"
            config conditional-advertise
                edit "222v4"
                    set condition-routemap "4-281" "6-281"
                    set condition-type exist
                next
            end
        next
    end
end

The FortiGate will only check the IPv4 RIB table to see if there is a matching IP address for each route map. Any IPv6 address under the route map will not get checked in the corresponding IPv6 RIB table, and the condition result will be non-existent. The 222v4 route map will not advertise to its neighbor because the result is non-existent, while the condition type is existent.

When the condition type is set to non-exist:

config router bgp
	set cross-family-conditional-adv disable
	config neighbor
        edit "2003::2:2:2:2"
            config conditional-advertise6
                edit "v6-222"
                    set condition-routemap "v6-238" "v4-287"
                    set condition-type non-exist
                next
            end
        next
    end
end

If the v6-238 IPv6 prefix does not exist in the IPv6 RIB table, then the FortiGate will only check v4-287 in the IPv6 RIB table. The FortiGate will not find it because it is an IPv4 address. Since the condition type is also non-exist, route v6-222 will be advertised to its neighbor.