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This articles explains the difference in syslog messages between Junos 12.3 and 13.3 regarging the generation of BGP notification messages by a device for any unconfigured peer's connection attempt.
Consider the following topology:
Case 1
R1 ----------------------------------------------- R2.
R1's configuration has R2 as BGP peer:
root@R1> show configuration system syslog file messages
any any;
root@R1> show interfaces terse fxp0
Interface Admin Link Proto Local Remote
fxp0 up up
fxp0.0 up up inet 10.219.37.219/26
root@R1> show configuration protocols bgp
group kb {
type internal;
local-address 10.219.37.219;
neighbor 10.219.22.222;
}
root@R1> show configuration routing-options autonomous-system
65015;
R2 running on Junos 12.3R4.6, where R1 is not configured as its neighbor:
root@R2> show version
Hostname: R2
Model: mx80
JUNOS Base OS boot [12.3R6]
root@R2> show configuration system syslog file messages
any any;
root@R2> show interfaces terse fxp0
Interface Admin Link Proto Local Remote
fxp0 up up
fxp0.0 up up inet 10.219.22.222/26
root@R2> show configuration routing-options autonomous-system
65015;
root@R2> show configuration protocols bgp
group kb {
type internal;
local-address 10.219.22.222;
}
When R1 tries to establish BGP with R2 as per the above configuration, BGP will be stuck in active state as below:
root@R1> show bgp summary
Groups: 1 Peers: 1 Down peers: 1
Table Tot Paths Act Paths Suppressed History Damp State Pending
inet.0
0 0 0 0 0 0
Peer AS InPkt OutPkt OutQ Flaps Last Up/Dwn State|#Active/Received/Accepted/Damped...
10.219.22.222 65015 0 1 0 0 24 Active
Further the R1 log message will show BGP connection is not getting established. However the reason is unclear.
Sep 7 23:29:13.683 R1 rpd[5551]: bgp_recv: peer 10.219.22.222 (Internal AS 65015): received unexpected EOF
From the log messages of R2, a message is logged which will indicates why the configuration is rejected. However, a notification message is not generated by R2 to be sent to R1:
Sep 7 23:29:13.678 2017 R2 rpd[1380]: bgp_listen_accept: Connection attempt from unconfigured neighbor: 10.219.37.219+61487
Starting with Junos 13.3, enhancements to log messages have been added for R2 to send a notification message that will provide the exact reason why BGP is not getting established.
Considering the same topology:
R1 ----------------------------------------------- R2
root@R1> show configuration system syslog file messages
any any;
root@R1> show interfaces terse fxp0
Interface Admin Link Proto Local Remote
fxp0 up up
fxp0.0 up up inet 10.219.37.219/26
root@R1> show configuration protocols bgp
group kb {
type internal;
local-address 10.219.37.219;
neighbor 10.219.22.222;
}
root@R1> show configuration routing-options autonomous-system
65015
R2 is running on Junos 13.3 (or above) and R1 is not configured as BGP peer/neighbor under BGP configuration of R2:
root@R2> show version
Hostname: R2
Model: mx80
JUNOS Base OS boot [13.3R6.5]
root@R2> show configuration system syslog file messages
any any;
root@R2> show interfaces terse fxp0
Interface Admin Link Proto Local Remote
fxp0 up up
fxp0.0 up up inet 10.219.22.222/26
root@R2> show configuration routing-options autonomous-system
65015
root@R2> show configuration protocols bgp
group kb {
type internal;
local-address 10.219.22.222;
}
root@R2> show bgp summary
Groups: 1 Peers: 1 Down peers: 1
Table Tot Paths Act Paths Suppressed History Damp State Pending
inet.0
0 0 0 0 0 0
Peer AS InPkt OutPkt OutQ Flaps Last Up/Dwn State|#Active/Received/Accepted/Damped...
10.219.22.222 65015 0 2 0 0 19:12 Active
Log messages in R2 clearly shows a notification message being generated and sent as unicast to R1:
Sep 7 23:52:29 R2 rpd[1380]: bgp_listen_accept: Connection attempt from unconfigured neighbor: 10.219.37.219+52956
Sep 7 23:52:29 R2 rpd[1380]: bgp_listen_accept:4572: NOTIFICATION sent to 10.219.37.219+52956 (proto): code 6 (Cease) subcode 5 (Connection Rejected), Reason: Connection attempt from unconfigured neighbor: 10.219.37.219+52956
Log messages in R1 indicate that BGP connection is rejected by the peer device:
Sep 7 23:52:29 R1 rpd[5551]: bgp_recv_open: peer 10.219.22.222 (Internal AS 65015): received NOTIFICATION code 6 (Cease) subcode 5 (Connection Rejected)
2020-10-23: Article reviewed for accuracy, no changes required; article accurate and valid