BGP peering flapping between Azure Route Server & NVA(Cisco 8000v router)

Question

BGP peering flapping between Azure Route Server & NVA(Cisco 8000v router).

Logs from router VM

*Sep 22 13:20:23.119: %BGP-5-ADJCHANGE: neighbor 10.0.2.4 Up
*Sep 22 13:20:42.081: %BGP-5-NBR_RESET: Neighbor 10.0.2.4 reset (Peer closed the session)
*Sep 22 13:20:42.082: %BGP-5-ADJCHANGE: neighbor 10.0.2.4 Down Peer closed the session
*Sep 22 13:20:42.082: %BGP_SESSION-5-ADJCHANGE: neighbor 10.0.2.4 IPv4 Unicast topology base removed from session Peer closed the session
*Sep 22 13:20:44.857: %BGP-5-ADJCHANGE: neighbor 10.0.2.5 Up
*Sep 22 13:21:03.802: %BGP-5-NBR_RESET: Neighbor 10.0.2.5 reset (Peer closed the session)
*Sep 22 13:21:03.803: %BGP-5-ADJCHANGE: neighbor 10.0.2.5 Down Peer closed the session
*Sep 22 13:21:03.803: %BGP_SESSION-5-ADJCHANGE: neighbor 10.0.2.5 IPv4 Unicast topology base removed from session Peer closed the session
*Sep 22 13:21:04.742: %BGP-5-ADJCHANGE: neighbor 10.0.2.4 Up
*Sep 22 13:21:23.671: %BGP-5-NBR_RESET: Neighbor 10.0.2.4 reset (Peer closed the session)
*Sep 22 13:21:23.671: %BGP-5-ADJCHANGE: neighbor 10.0.2.4 Down Peer closed the session
*Sep 22 13:21:23.671: %BGP_SESSION-5-ADJCHANGE: neighbor 10.0.2.4 IPv4 Unicast topology base removed from session Peer

Answer 1

BGP config on virtual router as below

router bgp 65501
bgp log-neighbor-changes
neighbor 10.0.2.4 remote-as 65515
neighbor 10.0.2.4 ebgp-multihop 255
neighbor 10.0.2.5 remote-as 65515
neighbor 10.0.2.5 ebgp-multihop 255
!
address-family ipv4
neighbor 10.0.2.4 activate
neighbor 10.0.2.5 activate
exit-address-family

Answer 2

@Kannan Thank you for reaching out to Microsoft Q&A. I understand that you are having issues with BGP flapping between the ASR and your NVA.

The cause of the flapping could be because of the BGP timer setting. By default, the Keep-alive timer on Azure Route Server is set to 60 seconds and the Hold-down timer is 180 seconds.
Could you please verify these settings on the NVA and try to change it to these values and see if this helps? Please let us know. Thank you!

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Answer 3

@SaiKishor-MSFT Timers are set to 60/180 but still the session is flapping

R1#sh ip bgp neighbors 10.0.2.4
BGP neighbor is 10.0.2.4, remote AS 65515, external link
BGP version 4, remote router ID 10.0.2.4
BGP state = Established, up for 00:00:17
Last read 00:00:17, last write 00:00:17, hold time is 180, keepalive interval is 60 seconds
Last update received: 00:00:17
Neighbor sessions:
1 active, is not multisession capable (disabled)
Neighbor capabilities:
Route refresh: advertised and received(new)
Four-octets ASN Capability: advertised and received
Address family IPv4 Unicast: advertised and received
Address family IPv6 Unicast: received
Enhanced Refresh Capability: advertised
Multisession Capability:
Stateful switchover support enabled: NO for session 1
Message statistics:

Answer 4

@Kannan Can you confirm if you have a static route added as mentioned below:

In some NVA, you need to add a static route for the Azure Route Server subnet. For example, if Azure Route Server is in 10.0.255.0/27 and your NVA is in 10.0.1.0/24, you need to add the following route to the routing table in the NVA:

Route Next Hop
10.0.255.0/27 10.0.1.1

10.0.1.1 is the default gateway IP in the subnet where your NVA (or more precisely, one of the NICs) is hosted.

Please let me know if this helps. Thank you!