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BFD session down between NE20 and NE40

Publication Date:  2017-09-25 Views:  80 Downloads:  0
Issue Description

Customer is facing problem with BFD.

He configured BFD between devices.

 

R-PS (NE20E-S2F) - R1-main_US-TEST (NE40E-X3)

R-PS_VS1 (NE20E-S2F) - R2-backup_US-TEST (NE20E-S2F)

R-PS (NE20E-S2F) - R-PS_VS1 (NE20E-S2F)

 

Dynamic BFD between same platforms (NE20 – NE20) works normal, but between NE20 – NE40 BFD session can’t be established.

He tried to configure static BFD for 4 VPN-Instances between R1-main_US-TEST (NE40E-X3) to  R-PS (NE20E-S2F). On NE20 BFD status is up, on NE40 is still DOWN.

Alarm Information


Handling Process

In the configuration on NE20E-S2F, we found customer configured the ebgp-max-hop and the device has patched the V800R008SPH016. It is a known problem that listed in the patch description like below.


V800R008SPH016

17

DTS2017060113154

In a BFD for BGP scenario, the local device uses a loopback interface's IP address to establish a confederation EBGP peer relationship with the IP address of a directly-connected remote interface. In this case, the BFD session goes Down.

The BFD session goes Down.

The problem occurs if the following conditions are met:
1. BFD for BGP is configured.
2. The local device uses a loopback interface's IP address to establish a confederation EBGP peer relationship with the IP address of a directly-connected remote interface.

In the preceding scenario, the local device tries to establish a single-hop BFD session, whereas the peer device tries to establish a multi-hop BFD session. The BFD session type inconsistency causes the problem.

The type of the BFD session between the directly connected EBGP peers has been changed from single-hop to multi-hop in the preceding situation.

None

Minor

BGP

If the problem has occurred, install the patch, and reconfigurethe peer { group-name | ipv4-address | ipv6-address } ebgp-max-hop [ hop-count ] or peer {group-name | ipv4-address | ipv6-address }valid-ttl-hops [hops ] to change the type of the BFD session between the directly connected EBGP peers from single-hop to multi-hop.

N/A

Perform reconfiguration.



Root Cause

FirstPeer ebgp max-hop is configured for the peerswhich are not connected directly. Under your scenario, both NE40E and NE20E arewith the same IP network. So you don’t have to configure such command. 

Second, the patch installed on all NE20E is V800R008SPH016.This patch has a mechanism highlighted as below. 

If the problem has occurred, install the patch, and reconfigurethe peer { group-name | ipv4-address | ipv6-address } ebgp-max-hop [ hop-count ] or peer {group-name | ipv4-address | ipv6-address }valid-ttl-hops [hops ] to change the type of the BFD session between the directly connected EBGP peers from single-hop to multi-hop.


Solution

If thers is a configuration on NE20E - "peer { group-name| ipv4-address | ipv6-address } ebgp-max-hop ", bfd will be multi-hop , but on NE40E it still be one-hop bfd ;

Customer can delete this configuration to solve this issue if needing normal ebgp.

END