ON THIS PAGE
Example: Configuring a Routing Policy Based on the Number of BGP Communities
This example shows how to create a policy that accepts BGP routes based on the number of BGP communities.
Requirements
No special configuration beyond device initialization is required before you configure this example.
Overview
This example shows two routing devices with an external BGP (EBGP) connection between them. Device R2 uses the BGP session to send two static routes to Device R1. On Device R1, an import policy specifies that the BGP-received routes can contain up to five communities to be considered a match. For example, if a route contains three communities, it is considered a match and is accepted. If a route contains six or more communities, it is considered a nonmatch and is rejected.
It is important to remember that the default policy for EBGP
is to accept all routes. To ensure that the nonmatching routes are
rejected, you must include a then reject action at the
end of the policy definition.
Topology
Figure 1 shows the sample network.
Configuration
CLI Quick Configuration
To quickly
configure this example, copy the following commands, paste them into
a text file, remove any line breaks, change any details necessary
to match your network configuration, and then copy and paste the commands
into the CLI at the [edit] hierarchy level.
Device R1
set interfaces fe-1/1/0 unit 0 description to-R2 set interfaces fe-1/1/0 unit 0 family inet address 10.0.0.1/30 set interfaces lo0 unit 0 family inet address 192.168.0.1/32 set protocols bgp group external-peers type external set protocols bgp group external-peers peer-as 2 set protocols bgp group external-peers neighbor 10.0.0.2 import import-communities set policy-options policy-statement import-communities term 1 from protocol bgp set policy-options policy-statement import-communities term 1 from community-count 5 orlower set policy-options policy-statement import-communities term 1 then accept set policy-options policy-statement import-communities term 2 then reject set routing-options router-id 192.168.0.1 set routing-options autonomous-system 1
Device R2
set interfaces fe-1/1/0 unit 0 description to-R1 set interfaces fe-1/1/0 unit 0 family inet address 10.0.0.2/30 set interfaces lo0 unit 0 family inet address 192.168.0.2/32 set protocols bgp group external-peers type external set protocols bgp group external-peers export statics set protocols bgp group external-peers peer-as 1 set protocols bgp group external-peers neighbor 10.0.0.1 set policy-options policy-statement statics from protocol static set policy-options policy-statement statics then community add 1 set policy-options policy-statement statics then accept set policy-options community 1 members 2:1 set policy-options community 1 members 2:2 set policy-options community 1 members 2:3 set policy-options community 1 members 2:4 set policy-options community 1 members 2:5 set policy-options community 1 members 2:6 set policy-options community 1 members 2:7 set policy-options community 1 members 2:8 set policy-options community 1 members 2:9 set policy-options community 1 members 2:10 set routing-options static route 10.2.0.0/16 reject set routing-options static route 10.2.0.0/16 install set routing-options static route 10.3.0.0/16 reject set routing-options static route 10.3.0.0/16 install set routing-options router-id 192.168.0.3 set routing-options autonomous-system 2
Procedure
Step-by-Step Procedure
The following example requires that you navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Using the CLI Editor in Configuration Mode in the Junos OS CLI User Guide.
To configure Device R1:
Configure the interfaces.
[edit interfaces] user@R1# set fe-1/1/0 unit 0 description to-R2 user@R1# set fe-1/1/0 unit 0 family inet address 10.0.0.1/30 user@R1# set lo0 unit 0 family inet address 192.168.0.1/32
Configure BGP.
Apply the import policy to the BGP peering session with Device R2.
[edit protocols bgp group external-peers] user@R1# set type external user@R1# set peer-as 2 user@R1# set neighbor 10.0.0.2 import import-communities
Configure the routing policy that sends direct routes.
[edit policy-options policy-statement import-communities] user@R1# set term 1 from protocol bgp user@R1# set term 1 from community-count 5 orlower user@R1# set term 1 then accept user@R1# set term 2 then reject
Configure the autonomous system (AS) number and the router ID.
[edit routing-options ] user@R1# set router-id 192.168.0.1 user@R1# set autonomous-system 1
Step-by-Step Procedure
The following example requires that you navigate various levels in the configuration hierarchy. For information about navigating the CLI, see Using the CLI Editor in Configuration Mode in the Junos OS CLI User Guide.
To configure Device R2:
Configure the interfaces.
[edit interfaces] user@R2# set fe-1/1/0 unit 0 description to-R1 user@R2# set fe-1/1/0 unit 0 family inet address 10.0.0.2/30 user@R2# set lo0 unit 0 family inet address 192.168.0.2/32
Configure the router ID and the autonomous system (AS) number.
[edit routing-options] user@R2# set router-id 192.168.0.3 user@R2# set autonomous-system 2
Configure BGP.
[edit protocols bgp group external-peers] user@R2# set type external user@R2# set peer-as 1 user@R2# set neighbor 10.0.0.1
Configure multiple communities, or configure a single community with multiple members.
[edit policy-options community 1] user@R2# set members 2:1 user@R2# set members 2:2 user@R2# set members 2:3 user@R2# set members 2:4 user@R2# set members 2:5 user@R2# set members 2:6 user@R2# set members 2:7 user@R2# set members 2:8 user@R2# set members 2:9 user@R2# set members 2:10
Configure the static routes.
[edit routing-options static] user@R2# set route 10.2.0.0/16 reject user@R2# set route 10.2.0.0/16 install user@R2# set route 10.3.0.0/16 reject user@R2# set route 10.3.0.0/16 install
Configure a routing policy that advertises static routes into BGP and adds the BGP community to the routes.
[edit policy-options policy-statement statics] user@R2# set from protocol static user@R2# set then community add 1 user@R2# set then accept
Apply the export policy.
[edit protocols bgp group external-peers] user@R2# set export statics
Results
From configuration mode, confirm your configuration
by entering the show interfaces, show protocols, show policy-options, and show routing-options commands. If the output does not display the intended configuration,
repeat the instructions in this example to correct the configuration.
Device R1
user@R1# show interfaces
fe-1/1/0 {
unit 0{
description to-R2;
family inet {
address 10.0.0.1/30;
}
}
}
lo0 {
unit 0 {
family inet {
address 192.168.0.1/32;
}
}
}
}
user@R1# show protocols
bgp {
group external-peers {
type external;
peer-as 2;
neighbor 10.0.0.2 {
import import-communities;
}
}
}
user@R1# show policy-options
policy-statement import-communities {
term 1 {
from {
protocol bgp;
community-count 5 orlower;
}
then accept;
}
term 2 {
then reject;
}
}
user@R1# show routing-options router-id 192.168.0.1; autonomous-system 1;
Device R2
user@R2# show interfaces
fe-1/1/0 {
unit 0 {
description to-R1;
family inet {
address 10.0.0.2/30;
}
}
}
lo0 {
unit 0 {
family inet {
address 192.168.0.2/32;
}
}
}
user@R2# show protocols
bgp {
group external-peers {
type external;
export statics;
peer-as 1;
neighbor 10.0.0.1;
}
}
user@R2# show policy-options
policy-statement statics {
from protocol static;
then {
community add 1;
accept;
}
}
community 1 members [ 2:1 2:2 2:3 2:4 2:5 2:6 2:7 2:8 2:9 2:10 ];
user@R2# show routing-options
static {
route 10.2.0.0/16 {
reject;
install;
}
route 10.3.0.0/16 {
reject;
install;
}
}
router-id 192.168.0.3;
autonomous-system 2;
If you are done configuring the devices, enter commit from configuration mode.
Verification
Confirm that the configuration is working properly.
Verifying the BGP Routes
Purpose
Make sure that the routing table on Device R1 contains the expected BGP routes.
Action
On Device R1, run the
show route protocols bgpcommand.user@R1> show route protocols bgp inet.0: 5 destinations, 5 routes (3 active, 0 holddown, 2 hidden)
On Device R1, change the
community-countconfiguration in the import policy.[edit policy-options policy-statement import-communities term 1] user@R1# set from community-count 5 orhigher user@R1# commit
On Device R1, run the
show route protocols bgpcommand.user@R1> show route protocols bgp inet.0: 5 destinations, 5 routes (5 active, 0 holddown, 0 hidden) + = Active Route, - = Last Active, * = Both 10.2.0.0/16 *[BGP/170] 18:29:53, localpref 100 AS path: 2 I, validation-state: unverified > to 10.0.0.2 via fe-1/1/0.0 10.3.0.0/16 *[BGP/170] 18:29:53, localpref 100 AS path: 2 I, validation-state: unverified > to 10.0.0.2 via fe-1/1/0.0On Device R1, run the
show route protocols bgp extensivecommand to view the advertised communities.user@R1> show route protocols bgp extensive inet.0: 5 destinations, 5 routes (5 active, 0 holddown, 0 hidden) 10.2.0.0/16 (1 entry, 1 announced) TSI: KRT in-kernel 10.2.0.0/16 -> {10.0.0.2} *BGP Preference: 170/-101 Next hop type: Router, Next hop index: 671 Address: 0x9458270 Next-hop reference count: 4 Source: 10.0.0.2 Next hop: 10.0.0.2 via fe-1/1/0.0, selected Session Id: 0x100001 State: <Active Ext> Local AS: 1 Peer AS: 2 Age: 18:56:10 Validation State: unverified Task: BGP_2.10.0.0.2+179 Announcement bits (1): 0-KRT AS path: 2 I Communities: 2:1 2:2 2:3 2:4 2:5 2:6 2:7 2:8 2:9 2:10 Accepted Localpref: 100 Router ID: 192.168.0.3 10.3.0.0/16 (1 entry, 1 announced) TSI: KRT in-kernel 10.3.0.0/16 -> {10.0.0.2} *BGP Preference: 170/-101 Next hop type: Router, Next hop index: 671 Address: 0x9458270 Next-hop reference count: 4 Source: 10.0.0.2 Next hop: 10.0.0.2 via fe-1/1/0.0, selected Session Id: 0x100001 State: <Active Ext> Local AS: 1 Peer AS: 2 Age: 18:56:10 Validation State: unverified Task: BGP_2.10.0.0.2+179 Announcement bits (1): 0-KRT AS path: 2 I Communities: 2:1 2:2 2:3 2:4 2:5 2:6 2:7 2:8 2:9 2:10 Accepted Localpref: 100 Router ID: 192.168.0.3
Meaning
The output shows that in Device R1’s routing
table, the BGP routes sent from Device R2 are hidden. When the community-count setting in Device R1’s import policy
is modified, the BGP routes are no longer hidden.