FRR can't seem to find pre-existing vxlan interface in the network namespace

[hujun-open]

Hi,
I am running FRR EVPN (v10.4.1) using network namespace as the VRF backend , and found a strange issue that it seems FRR can't find the per-existing vxlan interface in the NS, for example:

vpc-tunnel1# show vrf
netns-based vrfs
vrf blue id 2 netns /run/netns/blue (configured)
vpc-tunnel1# show vrf vni
VRF                                   VNI        VxLAN IF             L3-SVI               State Rmac
blue                                  101        None                 None                 Down  None

but there is vxlan interface in the NS:

root@vpc-tunnel1:~/vrf# ip netns exec blue ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
6: bluebr: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default qlen 1000
    link/ether 86:73:13:f4:7b:bd brd ff:ff:ff:ff:ff:ff
7: vni101: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue master bluebr state UNKNOWN mode DEFAULT group default qlen 1000
    link/ether 86:73:13:f4:7b:bd brd ff:ff:ff:ff:ff:ff

however if delete and recreate the bluebr and vni101 interface while FRR is running, then it works:

root@vpc-tunnel1:~/vrf# ip netns exec blue ip link del vni101
root@vpc-tunnel1:~/vrf# ip netns exec blue ip link del bluebr
root@vpc-tunnel1:~/vrf# ip netns exec blue ip link add bluebr type bridge
root@vpc-tunnel1:~/vrf# ip netns exec blue ip link add vni101 type vxlan local 192.168.1.100 dstport 4789 id 101 nolearning
root@vpc-tunnel1:~/vrf# ip netns exec blue ip link set vni101 master bluebr addrgenmode none
root@vpc-tunnel1:~/vrf# ip netns exec blue ip link set vni101 type bridge_slave neigh_suppress on learning off
root@vpc-tunnel1:~/vrf# ip netns exec blue ip link set vni101 up
root@vpc-tunnel1:~/vrf# ip netns exec blue ip link set bluebr up

//vtysh
vpc-tunnel1# show vrf vni
VRF                                   VNI        VxLAN IF             L3-SVI               State Rmac
blue                                  101        vni101               bluebr               Up    be:7b:7c:c9:b4:f7

now if I restart FRR, then it goes down again:

root@vpc-tunnel1:~/vrf# systemctl restart frr
//vtysh
vpc-tunnel1# show vrf vni
VRF                                   VNI        VxLAN IF             L3-SVI               State Rmac
blue                                  101        None                 None                 Down  None

I wonder what is the issue here?

following is my FRR config:

vpc-tunnel1# show running-config
Building configuration...

Current configuration:
!
frr version 10.4.1
frr defaults traditional
hostname vpc-tunnel1
log file /var/log/frr/d.log
log syslog
service integrated-vtysh-config
!
debug zebra events
debug zebra kernel
debug zebra vxlan
debug zebra evpn mh nh
debug zebra nexthop detail
!
vrf blue
 vni 101
exit-vrf
!
router bgp 100
 neighbor 192.168.1.1 remote-as internal
 !
 address-family l2vpn evpn
  neighbor 192.168.1.1 activate
  advertise-all-vni
  advertise-svi-ip
 exit-address-family
exit
!
router bgp 100 vrf blue
 !
 address-family ipv4 unicast
  redistribute kernel
 exit-address-family
 !
 address-family l2vpn evpn
  advertise ipv4 unicast
  rd 192.168.1.100:101
 exit-address-family
exit
!
end