Can the disappearance of a connected route or the LAN port link being down trigger iBGP to perform r

[Bruce7x2]

I wanted to achieve fast route updates in iBGP when the LAN link goes down, but I failed. I couldn't figure out when the route updates actually happen. Additionally, I would like to know if it is feasible in my environment to have immediate route updates when the LAN link goes down.

To be precise, at what point in time does iBGP initiate the update when the LAN port (Connected Route) of Remote-LAN disappears? Based on my testing, it is evident that the routes are not updated immediately; in other words, the withdrawn message does not appear immediately.

Moreover, is the triggering of iBGP route updates by the disappearance of connected routes related to information such as "[RIB] Scanning BGP Network Routes" and "[RIB] Scanning BGP RIB"?

Topology:

(BGP over VPN)(LAN)FGHG(WAN)----(VPN)---(WAN)Remote-FG(LAN)(BGP over VPN)

Here are the downtime durations I observed in the terminal device ping tests after performing a link down in Remote-FG.

TEST	downtime of ping test
1	5s
2	12s
3	5s

<TEST1>

○Femote-FG LAN Port Link Down

2023-06-27 15:25:17 BGP:  Message type: Link Down (30)

...

2023-06-27 15:25:17 BGP: 11.25.100.6-Outgoing [FSM] State: Established Event: 34

2023-06-27 15:25:17 BGP: 11.25.100.6-Outgoing [ENCODE] Msg-Hdr: Type 2

2023-06-27 15:25:17 BGP: 11.25.100.6-Outgoing [ENCODE] Update Withdrawn: Prefix 172.124.1000.0/24

2023-06-27 15:25:17 BGP: 11.25.100.6-Outgoing [ENCODE] Update: Msg #35 Size 27

...

2023-06-27 15:25:18 BGP: [RIB] Scanning BGP Network Routes...

2023-06-27 15:25:19 BGP: NSM Message Header

...

2023-06-27 15:25:31 BGP: 12.25.100.14-Outgoing [ENCODE] Msg-Hdr: Type 2

2023-06-27 15:25:31 BGP: 12.25.100.14-Outgoing [ENCODE] Update Withdrawn: Prefix 172.124.1000.0/24

2023-06-27 15:25:31 BGP: 12.25.100.14-Outgoing [ENCODE] Update: Msg #36 Size 27

...

2023-06-27 15:25:33 BGP: [RIB] Scanning BGP Network Routes...

diag ip router bgp level none

○FGHG

2023-06-27 15:25:17 BGP: 11.25.100.22-Outgoing [ENCODE] Msg-Hdr: Type 4

2023-06-27 15:25:17 BGP: 11.25.100.22-Outgoing [ENCODE] Keepalive: 21264 KAlive msg(s) sent

2023-06-27 15:25:17 BGP: 11.25.100.22-Outgoing [DECODE] Msg-Hdr: type 2, length 27

2023-06-27 15:25:17 BGP: 11.25.100.22-Outgoing [DECODE] Update: Starting UPDATE decoding... Bytes To Read (8), msg_size (8)

2023-06-27 15:25:17 BGP: 11.25.100.22-Outgoing [DECODE] Update: Withdrawn Len(4)

2023-06-27 15:25:17 BGP: 11.25.100.22-Outgoing [FSM] State: Established Event: 27

2023-06-27 15:25:17 BGP: 11.25.100.22-Outgoing [RIB] Withdraw: Prefix 172.124.100.0/24 path_id 0

2023-06-27 15:25:17 BGP: [DAMP] bgp_rfd_rt_withdraw(): Non EBGP Peer, no dampening reqd

2023-06-27 15:25:17 BGP: [DAMP] bgp_rfd_rt_withdraw(): Route State: NONE, ret=0

2023-06-27 15:25:17 BGP: BGP VRF 0 leaking 172.124.100.0/24 afi 1, safi 1

2023-06-27 15:25:17 BGP: VRF 0 NSM withdraw: 172.124.100.0/24

2023-06-27 15:25:17 BGP: 11.25.100.22-Outgoing [DECODE] Msg-Hdr: type 4, length 19

2023-06-27 15:25:17 BGP: 11.25.100.22-Outgoing [DECODE] KAlive: Received!

2023-06-27 15:25:17 BGP: 11.25.100.22-Outgoing [FSM] State: Established Event: 26

<TEST2>

○Remote-FG LAN Port Link Down

2023-06-27 15:33:14 BGP:  Message type: Link Down (30)

...

2023-06-27 15:33:17 BGP: 12.25.100.14-Outgoing [ENCODE] Msg-Hdr: Type 2

2023-06-27 15:33:17 BGP: 12.25.100.14-Outgoing [ENCODE] Update Withdrawn: Prefix 172.124.100.0/24

2023-06-27 15:33:17 BGP: 12.25.100.14-Outgoing [ENCODE] Update: Msg #38 Size 27

...

2023-06-27 15:33:18 BGP: [RIB] Scanning BGP Network Routes...

...

2023-06-27 15:33:24 BGP: 11.25.100.6-Outgoing [ENCODE] Msg-Hdr: Type 2

2023-06-27 15:33:24 BGP: 11.25.100.6-Outgoing [ENCODE] Update Withdrawn: Prefix 172.124.100.0/24

2023-06-27 15:33:24 BGP: 11.25.100.6-Outgoing [ENCODE] Update: Msg #37 Size 27

...

2023-06-27 15:33:33 BGP: [RIB] Scanning BGP Network Routes...

..

○FGHG

2023-06-27 15:33:24 BGP: 11.250.1.22-Outgoing [DECODE] Msg-Hdr: type 2, length 27

2023-06-27 15:33:24 BGP: 11.250.1.22-Outgoing [DECODE] Update: Starting UPDATE decoding... Bytes To Read (8), msg_size (8)

2023-06-27 15:33:24 BGP: 11.250.1.22-Outgoing [DECODE] Update: Withdrawn Len(4)

2023-06-27 15:33:24 BGP: 11.250.1.22-Outgoing [FSM] State: Established Event: 27

2023-06-27 15:33:24 BGP: 11.250.1.22-Outgoing [RIB] Withdraw: Prefix 172.124.100.0/24 path_id 0

2023-06-27 15:33:24 BGP: [DAMP] bgp_rfd_rt_withdraw(): Non EBGP Peer, no dampening reqd

2023-06-27 15:33:24 BGP: [DAMP] bgp_rfd_rt_withdraw(): Route State: NONE, ret=0

2023-06-27 15:33:24 BGP: BGP VRF 0 leaking 172.124.100.0/24 afi 1, safi 1

2023-06-27 15:33:24 BGP: VRF 0 NSM withdraw: 172.124.100.0/24

....

2023-06-27 15:33:26 BGP: [RIB] Scanning BGP Network Routes...

...

2023-06-27 15:33:33 BGP: [RIB] Scanning BGP RIB...

...

diag ip router bgp level none

FGHQ1 # diag debug reset

<TEST3>

○Remote-FG LAN Port Link Down

2023-06-27 15:53:00 BGP:  Message type: Link Down (30)

...

2023-06-27 15:53:03 BGP: [RIB] Scanning BGP Network Routes...

...

2023-06-27 15:53:04 BGP: 11.25.100.6-Outgoing [ENCODE] Msg-Hdr: Type 2

2023-06-27 15:53:04 BGP: 11.25.100.6-Outgoing [ENCODE] Update Withdrawn: Prefix 172.124.100.0/24

2023-06-27 15:53:04 BGP: 11.25.100.6-Outgoing [ENCODE] Update: Msg #39 Size 27

...

2023-06-27 15:53:05 BGP: [RIB] Scanning BGP RIB...

2023-06-27 15:53:05 BGP: [NSM] Verified NH 11.25.100.6 with NSM

2023-06-27 15:53:05 BGP: [NSM] Verified NH 12.25.100.14 with NSM

○FGHG
 

2023-06-27 15:53:04 BGP: 11.25.100.22-Outgoing [DECODE] Msg-Hdr: type 2, length 27

2023-06-27 15:53:04 BGP: 11.25.100.22-Outgoing [DECODE] Update: Starting UPDATE decoding... Bytes To Read (8), msg_size (8)

2023-06-27 15:53:04 BGP: 11.25.100.22-Outgoing [DECODE] Update: Withdrawn Len(4)

2023-06-27 15:53:04 BGP: 11.25.100.22-Outgoing [FSM] State: Established Event: 27

2023-06-27 15:53:04 BGP: 11.25.100.22-Outgoing [RIB] Withdraw: Prefix 172.124.100.0/24 path_id 0

2023-06-27 15:53:04 BGP: [DAMP] bgp_rfd_rt_withdraw(): Non EBGP Peer, no dampening reqd

2023-06-27 15:53:04 BGP: [DAMP] bgp_rfd_rt_withdraw(): Route State: NONE, ret=0

2023-06-27 15:53:04 BGP: BGP VRF 0 leaking 172.124.100.0/24 afi 1, safi 1

2023-06-27 15:53:04 BGP: VRF 0 NSM withdraw: 172.124.100.0/24

...

2023-06-27 15:53:11 BGP: [RIB] Scanning BGP Network Routes...

...

2023-06-27 15:53:13 BGP: [RIB] Scanning BGP RIB...

[Jean-Philippe_P]

Hello Bruce7x2, 

Thank you for using the Community Forum. I will seek to get you an answer or help. We will reply to this thread with an update as soon as possible. 

Thanks, 

[Jean-Philippe_P]

Hello,

We are still looking for an answer to your question.

We will come back to you ASAP.

Thanks,

[saneeshpv_FTNT]

Hi,

Please try to adjust the timers (advertisement-interval) mentioned in the below article and perform your test again and see if it makes any difference.

https://community.fortinet.com/t5/FortiGate/Technical-Tip-Facilitating-the-fastest-BGP-route-failove...

This is applied on a per neighbor basis.

Best Regards,

San