Azure and Cisco Router not forming an express route BGP session

Gunther Fembini 0

For some reason my BGP session to Azure through an Express Route connection is not forming. Below is the configuration of the Express Route Circuit: Peer AS: 65000 Subnets: IPv4 Primary IPv4: 10.x.x.0/30 Secondary IPv4 10.x.x.4/30 Vlan ID: XXX Cisco router config: router bgp 65000 neighbor 10.x.x.2 remote-as 65515 address-family ipv4 neighbor 10.x.x.2 activate interface GigabitEthernet0/0/3.XXX encapsulation dot1q XXX ip address 10.x.x.1 255.255.255.252 I can ping from the router to the Azure express-route connection but BGP is not forming and I do not see any BGP messages from Azure when I debug BGP from the Cisco router. What am I not seeing here?

GitaraniSharma-MSFT 49,486 Reputation points Microsoft Employee

2024-02-19T10:51:27.3+00:00
Hello @Gunther Fembini ,

Welcome to Microsoft Q&A Platform. Thank you for reaching out & hope you are doing well.

I understand that you've set up an Azure ExpressRoute connection with private peering but BGP between Azure and Cisco router is not UP. As mentioned in the below Azure ExpressRoute troubleshooting doc,

If the state of an eBGP peering between an MSEE and a CE/PE-MSEE is Active or Idle, check if the assigned primary and secondary peer subnets match the configuration on the linked CE/PE-MSEE. Also check if the correct VlanId, AzureASN, and PeerASN values are used on MSEEs, and if these values map to the ones used on the linked CE/PE-MSEE. If MD5 hashing is chosen, the shared key should be the same on MSEE and CE/PE-MSEE pairs. If you need to change any of these configurations on an MSEE router, see Create and modify routing for an ExpressRoute circuit.

Refer: https://learn.microsoft.com/en-us/azure/expressroute/expressroute-troubleshooting-expressroute-overview#validate-bgp-and-routes-on-the-msee

Did you validate all your configuration?

On the Cisco router, what is the result of show ip bgp summary?

If the BGP state shows idle, then we may need to drill into the logs to find why the BGP peering is down between MSEE and CE.

Could you please also check the below details:

Is BFP (Bidirectional Forwarding Detection) configured properly?

Refer: https://learn.microsoft.com/en-us/azure/expressroute/expressroute-bfd#enabling-bfd

Are the Cisco interfaces configured properly to use eBGP and advertise routes to Microsoft?

Refer: https://learn.microsoft.com/en-us/azure/expressroute/expressroute-config-samples-routing#cisco-ios-xe-based-routers

Do you have shared key/MD5 hashing configured? If yes, the shared key should be the same on MSEE and CE/PE-MSEE pairs.

NOTE: The limit is a maximum of 25 alphanumeric characters. Special characters aren't supported.

Refer: https://learn.microsoft.com/en-us/azure/expressroute/expressroute-howto-routing-portal-resource-manager#private

I've also seen instances where customer configured BGP with the same ASN in local and remote BGP peers. From the customer configuration, the remote peer ASN must be Azure's 12076 ASN. Please validate the ASN configuration again.

Regards,

Gita
GitaraniSharma-MSFT 49,486 Reputation points Microsoft Employee

2024-02-20T11:32:33.0633333+00:00

@Gunther Fembini , could you please provide an update on this post?
Gunther Fembini 0 Reputation points

2024-02-21T16:46:30.9966667+00:00

Still no change. I get no messaging from the Azure side that it is even trying to form a BGP neighborship with my Cisco router. Cisco is trying to form a relationship meanwhile Azure is not even trying.
GitaraniSharma-MSFT 49,486 Reputation points Microsoft Employee

2024-02-22T11:46:28.94+00:00

@Gunther Fembini , is the ARP (Address Resolution Protocol) UP?

Refer: https://learn.microsoft.com/en-us/azure/expressroute/expressroute-troubleshooting-expressroute-overview#validate-arp

https://learn.microsoft.com/en-us/azure/expressroute/expressroute-troubleshooting-arp-resource-manager

If yes, could you please share what is the result of show ip bgp summary on the Cisco router?
GitaraniSharma-MSFT 49,486 Reputation points Microsoft Employee

2024-03-04T12:36:08.4766667+00:00

@Gunther Fembini , could you please provide an update on this issue?
JG 0 Reputation points

2024-09-09T13:07:50.94+00:00

any update on this

1 answer

Gulnaz Mushtaq 410 Reputation points MVP

2024-09-09T13:49:29+00:00

Hi @Gunther Fembini

First of all run the command show ip bgp summary on your Cisco router to check the BGP state. If it shows “Idle,” you may need to look into the logs for more details. Also, you need to verify that the NSGs on your Azure side are not blocking the BGP traffic.

You should also check whether the ARP is functioning correctly on both sides. Sometimes ARP issues can cause BGP sessions to fail.
Please sign in to rate this answer.

0 comments No comments
Sign in to comment

Use comments to ask for clarification, additional information, or improvements to the question.

Share via

Azure and Cisco Router not forming an express route BGP session

1 answer

Your answer