Verify BGP Peers

Purpose

Assuming that all the routers are correctly configured for BGP, you can verify if IBGP and EBGP sessions are properly established, external routes are advertised and received correctly, and the BGP path selection process is working properly.

Figure 15 illustrates an example BGP network topology used in this topic.

Figure 15: BGP Network Topology

The network consists of two directly connected ASs consisting of external and internal peers. The external peers are directly connected through a shared interface and are running EBGP. The internal peers are connected through their loopback (lo0) interfaces through IBGP. AS 65001 is running OSPF and AS 65002 is running IS-IS as its underlying IGP. IBGP routers do not have to be directly connected, the underlying IGP allows neighbors to reach one another.

The two routers in AS 65001 each contain one EBGP link to AS 65002 (R2 and R4) over which they announce aggregated prefixes: 100.100.1.0, 100.100.2.0, 100.100.3.0, and 100.100.4.0. Also, R1 and R5 are injecting multiple exit discriminator (MED) values of 5 and 10, respectively, for some routes.

The internal routers in both ASs are using a full mesh IBGP topology. A full mesh is required because the networks are not using confederations or route reflectors, so any routes learned through IBGP are not distributed to other internal neighbors. For example, when R3 learns a route from R2, R3 does not distribute that route to R6 because the route is learned through IBGP, so R6 must have a direct BGP connection to R2 to learn the route.

In a full mesh topology, only the border router receiving external BGP information distributes that information to other routers within its AS. The receiving router does not redistribute that information to other IBGP routers in its own AS.

From the point of view of AS 65002, the following sessions should be up:

• The four routers in AS 65002 should have IBGP sessions established with each other.
• R2 should have an EBGP session established with R1.
• R4 should have an EBGP session established with R5.

To verify BGP peers, follow these steps:

1. Check That BGP Sessions Are Up
2. Verify That a Neighbor is Advertising a Particular Route
3. Verify That a Particular BGP Route Is Received on Your Router

Check That BGP Sessions Are Up

Purpose

To check that all IBGP and EBGP sessions are properly established.

Action

To check that all IBGP and EBGP sessions are properly established, enter the following JUNOS CLI operational mode command:

The following sample output from R2 shows four peers that are not established:

Sample Output

user@R2> show bgp summary  
Groups: 2 Peers: 4  Down peers: 1
Table          Tot Paths  Act Paths Suppressed    History Damp State    Pending
inet.0                 6          4          0          0          0          0
Peer               AS      InPkt     OutPkt    OutQ   Flaps Last Up/Dwn State|#Active/Received/Damped...
10.0.0.3        65002         86         90       0       2       42:54 0/0/0                0/0/0
10.0.0.4        65002         90         91       0       1       42:54 0/2/0                0/0/0
10.0.0.6        65002         87         90       0       3           3 Active
10.1.12.1       65001         89         89       0       1       42:54 4/4/0                 0/0/0

The following sample output shows that all peers are established:

Sample Output

user@R2> show bgp summary 
Groups: 2 Peers: 4 Down peers: 0
Table          Tot Paths  Act Paths Suppressed    History Damp State    Pending
inet.0                 6          4          0          0          0          0
Peer               AS      InPkt     OutPkt    OutQ   Flaps Last Up/Dwn State|#Active/Received/Damped..
10.0.0.3        65002      54440      54457       0       1     2w4d21h 0/0/0                0/0/0
10.0.0.4        65002      51505      51507       0       0     2w3d21h 0/2/0                 0/0/0
10.0.0.6        65002      14066      14070       0       1 4d 21:15:14 0/0/0                0/0/0
10.1.12.1       65001      88580      88587       0       0     4w2d18h 4/4/0                0/0/0

user@R3>  show bgp summary 
Groups: 1 Peers: 3 Down peers: 0
Table          Tot Paths  Act Paths Suppressed    History Damp State    Pending
inet.0                 6          4          0          0          0          0
Peer               AS      InPkt     OutPkt    OutQ   Flaps Last Up/Dwn State|#Active/Received/Damped..
10.0.0.2        65002      54476      54460       0       1        7:17 4/4/0                0/0/0
10.0.0.4        65002      51527      51511       0       0     2w3d21h 0/2/0                0/0/0
10.0.0.6        65002      54459      54459       0       0     2w4d21h 0/0/0                0/0/0 

user@R4> show bgp summary 
Groups: 2 Peers: 4 Down peers: 0
Table          Tot Paths  Act Paths Suppressed    History Damp State    Pending
inet.0                 8          4          0          0          0          0
Peer               AS      InPkt     OutPkt    OutQ   Flaps Last Up/Dwn State|#Active/Received/Damped...
10.0.0.2        65002      51530      51532       0       1         8:59 2/4/0                0/0/0
10.0.0.3        65002      51512      51531       0       0     2w3d21h 0/0/0                0/0/0
10.0.0.6        65002      51515      51530       0       0     2w3d21h 0/0/0                0/0/0
10.1.45.2       65001      51520      51530       0       0      2w3d21h 2/4/0                 0/0/0

user@R6> show bgp summary  
Groups: 1 Peers: 3  Down peers: 0
Table          Tot Paths  Act Paths Suppressed    History Damp State    Pending
inet.0                 6          4          0          0          0          0
Peer               AS      InPkt     OutPkt    OutQ   Flaps Last Up/Dwn State|#Active/Received/Damped..
10.0.0.2        65002      88610      88587       0       2       10:30 2/4/0                0/0/0
10.0.0.3        65002      54464      54468       0       1     2w4d22h 0/0/0                0/0/0
10.0.0.4        65002      51532      51520       0       0     2w3d21h 2/2/0 

Meaning

Sample output 1 shows a peer that is not established, while sample output 2 shows that all IBGP and EBGP sessions shown in the network diagram in Figure 15 are established.

Sample output 1 shows one peer (10.0.0.6) is not established, as indicated by the Down Peers: 1 field. The State|#Active/Received/Damped column also displays Active, indicating that the peer is in the Active state and not yet established.

The State|#Active/Received/Damped) column is a dual purpose field, as indicated by the pipe (|). When a peer is not established (as in our example), the field indicates the state of the peering session, such as active, connect, or idle. When the peer is in the Established state, the field displays the number of active, received, or damped routes received from the neighbor. For example, peer 10.0.0.6 is an example of the last column displaying the Active state, and peer 10.1.12.1 is an example of the last column showing the number of active, received, and damped routes (4/4/0). For more detailed information on the show bgp summary command, see the JUNOS Routing Protocols and Policies Command Reference.

If the BGP neighbor session is not established, use the ping and show route commands to verify network connectivity to the BGP neighbor. Also, use the show log messages command to look for any errors pertaining to the peer in question.

Sample output 2 shows that all IBGP and EBGP sessions shown in the network diagram in Figure 15 are established, as indicated by the Down Peers: 0 field and the last column that shows the number of routes.

Following is a description of the output for all established BGP peers, R2, R3, R4, and R6.

The route information for border router R2 shows the following:

• 0/0/0 for internal peers 10.0.0.3 and 10.0.0.6, indicating that no BGP routes are received or active in the routing table from those peers. No BGP routes are damped.
• 0/2/0 for internal peer 10.0.0.4, indicating that two received BGP routes are not active in the routing table. No BGP routes are damped.
• 4/4/0 for external peer 10.1.12.1, indicating that four received BGP routes are active in the routing table. No BGP routes are damped.

The route information for internal router R3 shows the following:

• 0/0/0 for internal peer 10.0.0.6, indicating that no BGP routes are received or active in the routing table from that peer. No BGP routes are damped.
• 0/2/0 for internal peer 10.0.0.4, indicating that two received BGP routes are not active in the routing table. No BGP routes are damped.
• 4/4/0 for internal peer 10.0.0.2, indicating that four received BGP routes are active in the routing table. No BGP routes are damped.

The route information for border router R4 shows the following:

• 0/0/0 for internal peers 10.0.0.3 and 10.0.0.6, indicating that no BGP routes are received or active in the routing table from those peers. No BGP routes are damped.
• 2/4/0 for internal peer 10.0.0.2 and external peer 10.1.45.1, indicating that two BGP routes are active in the routing table, but four are received. No BGP routes are damped.

The route information for internal router R6 shows the following:

• 0/0/0 for internal peer 10.0.0.3, indicating that no BGP routes are received or active in the routing table from that peer. No BGP routes are damped.
• 2/4/0 for internal peers 10.0.0.2,and 10.0.0.4,indicating that of the four received BGP routes, two are active in the routing table. No BGP routes are damped.

Other information in the sample output includes the following:

• Number of configured BGP groups: R2 has two groups configured (internal and toR1), and R4 also has two BGP groups configured (internal and toR5).
• Number of BGP peers to which the router is linked: R2 and R4 have four (one EBGP and three IBGP), and R3 and R6 have three IBGP. One peer is down (R6) in sample output 1.
• The name of the routing table storing the BGP routes, all routers are using inet.0.
• The total number of BGP paths, for example, R4 has a total of eight BGP paths from all of its peers.
• The number of active BGP routes, for example, R4 has a total of four active BGP routes from all of its peers.
• The second column of values (0/0/0) in the State|#Active/Received/Damped field indicates the number of multiprotocol BGP (MBGP) routes. All routers do not have any received, active, or damped MBGP routes.

Verify That a Neighbor is Advertising a Particular Route

Purpose

You can determine if a particular route that you have configured is being advertised by a neighbor.

Action

To verify that a neighbor is advertising a particular route, enter the following JUNOS CLI operational mode command:

Sample Output

inet.0: 20 destinations, 22 routes (20 active, 0 holddown, 0 hidden)
  Prefix                  Nexthop              MED     Lclpref    AS path
* 100.100.1.0/24          Self                 5       200        65001 I
* 100.100.2.0/24          Self                 5       100        65001 I
* 100.100.3.0/24          Self                         100        65001 I
* 100.100.4.0/24          Self                         100        65001 I

Meaning

The sample output shows the BGP routes advertised from R2 to its neighbor, 10.0.0.4 (R4). Out of 22 total routes in the inet.0 routing table, 20 are active destinations . No routes are hidden or in the hold-down state. Routes reside in the hold-down state prior to being declared active, and routes rejected by a routing policy can be placed into the hidden state. The information displayed reflects the routes that the routing table exported to the BGP routing protocol.

Verify That a Particular BGP Route Is Received on Your Router

Purpose

Display the routing information as it is received through a particular BGP neighbor and advertised by the local router to the neighbor.

Action

To verify that a particular BGP route is received on your router, enter the following JUNOS CLI operational mode command:

Sample Output

inet.0: 18 destinations, 20 routes (18 active, 0 holddown, 0 hidden)
  Prefix                  Nexthop              MED     Lclpref    AS path
* 100.100.1.0/24          10.0.0.2             5       200        65001 I
* 100.100.2.0/24          10.0.0.2             5       100        65001 I
  100.100.3.0/24          10.0.0.2                     100        65001 I
  100.100.4.0/24          10.0.0.2                     100        65001 I
iso.0: 1 destinations, 1 routes (1 active, 0 holddown, 0 hidden)

user@R6> show route receive-protocol bgp 10.0.0.4  
inet.0: 18 destinations, 20 routes (18 active, 0 holddown, 0 hidden)
  Prefix                  Nexthop              MED     Lclpref    AS path
* 100.100.3.0/24           10.0.0.4                     100        65001 I
* 100.100.4.0/24          10.0.0.4                     100        65001 I
iso.0: 1 destinations, 1 routes (1 active, 0 holddown, 0 hidden)

Meaning

The sample output shows four BGP routes from R2 and two from R4. Of the four routes from R2, only two are active in the routing table, as indicated by the asterisk (*), while both routes received from R4 are active in the routing table. All BGP routes came through AS 65001.