An ISP may request a customer to advertise eBGP prefixes (routes) with a specific community value.  This community value is then used by the ISP to further apply specific policies to these prefixes.

(192.168.100.1) FW1 (20.1.1.2)--------(20.1.1.1) FW2
                      AS 1111          AS 2222

Conditions:

• FW1 and FW2 are eBGP peers
• FW1 is advertising its directly connected network, 192.168.100.0/24
• FW1 must advertise its directly connected network with Community value of "99"

The following configuration on FW1 will allow this:

1. Configure eBGP

   set vrouter trust-vr
set protocol bgp 1111
set enable
set neighbor 20.1.1.1 remote-as 2222
set neighbor 20.1.1.1 enable
exit

2. Configure BGP on interface
   set interface untrust protocol bgp

3. Create access list
   set vrouter trust-vr
set access-list 1
set access-list 1 permit ip 0.0.0.0/0 1
exit

4.  Create community-list
   set vrouter trust-vr
set protocol bgp 1111
set neighbor 20.1.1.1 send-community         
set community-list 1 permit 1111 99
exit
exit

5. Create route-map
   set vrouter trust-vr
set route-map name "routemap1" permit 1
set match ip 1
set community 1
exit

6. Apply route-map
   set vrouter trust-vr
set protocol bgp 1111
set neighbor 20.1.1.1 route-map "routemap1" out
exit
exit

7. Redistribute connected routes to BGP

   set vrouter trust-vr
set protocol bgp
set redistribute route-map "routemap1" protocol connected
exit     
exit

Here is the output from the eBGP peer (FW2).  Notice the community of 1111:99:

FW_2> get vrouter trust-vr protocol bgp rib 192.168.100.0/24
Prefix: 192.168.100.0/24
Nexthop: 20.1.1.2, Weight: 100, Local Pref: 100, MED: 0, Flags: 0x486 0x88, Orig: INCOMPLETE
AS segment type: AS_SEQ, AS path:1111
Community: 1111:99

2020-09-16: Article reviewed for accuracy. Minor changes made. Updated security products