Hello,

I have done some trials with Open vSwitch RSTP and BFD features. While the 
features work well independently, I have discovered that the features don't 
work well when enabled on the same switch instance.

It seems to be that when BFD is enabled on interface, RSTP considers that link 
down instantly and blocks all outgoing traffic on that interface.  
Unfortunately this includes also the outgoing BFD messages. This leads to 
situation BFD will never get the link up and RSTP will never be able to use the 
link.

Expected behaviour would be that BFD messages are send and received regardless 
of the RSTP state of a link. Eventually BFD would see link state up and RSTP 
could start to use the link.

Software version details:
CentOS 7.2 Linux
Linux version 3.10.0-327.36.3.el7.x86_64 (buil...@kbuilder.dev.centos.org) (gcc 
version 4.8.5 20150623 (Red Hat 4.8.5-4) (GCC) ) #1 SMP Mon Oct 24 16:09:20 UTC 
O
ovs-vswitchd (Open vSwitch) 2.5.1


How to reproduce problem:
Two (CentOS) hosts connected together with eno51 interface.

# On host_1
service firewalld stop
ifconfig eno51 192.168.0.11/24 up
ovs-vsctl add-br br2 -- set Bridge br2 rstp_enable=true
ifconfig br2 172.16.20.1/24 up
ovs-vsctl add-port br2 gre0 -- set interface gre0 type=gre 
options:remote_ip=192.168.0.12 options:key=1 bfd:enable=true

# On host_2
service firewalld stop
ifconfig eno51 192.168.0.12/24 up
ovs-vsctl add-br br2 -- set Bridge br2 rstp_enable=true
ifconfig br2 172.16.20.2/24 up
ovs-vsctl add-port br2 gre0 -- set interface gre0 type=gre 
options:remote_ip=192.168.0.11 options:key=1 bfd:enable=true


# BFD sees path down.
[root@host_1 ~]# ovs-appctl bfd/show
---- gre0 ----
        Forwarding: false
        Detect Multiplier: 3
        Concatenated Path Down: false
        TX Interval: Approx 1000ms
        RX Interval: Approx 1000ms
        Detect Time: now +5076509ms
        Next TX Time: now -52ms
        Last TX Time: now +728ms

        Local Flags: none
        Local Session State: down
        Local Diagnostic: No Diagnostic
        Local Discriminator: 0xfd19b281
        Local Minimum TX Interval: 1000ms
        Local Minimum RX Interval: 1000ms

        Remote Flags: none
        Remote Session State: down
        Remote Diagnostic: No Diagnostic
        Remote Discriminator: 0x0
        Remote Minimum TX Interval: 0ms
        Remote Minimum RX Interval: 1ms


[root@ host_1 ~]# ovs-dpctl show
system@ovs-system:
        lookups: hit:1739 missed:81 lost:0
        flows: 0
        masks: hit:2570 total:1 hit/pkt:1.41
        port 0: ovs-system (internal)
        port 1: br2 (internal)
        port 2: gre_sys (gre)

# RSTP has disabled the port
[root@ host_1 ~]# ovs-vsctl get Port gre0 rstp_status
{rstp_designated_bridge_id="0.000.000000000000", rstp_designated_path_cost="0", 
rstp_designated_port_id="0000", rstp_port_id="8001", rstp_port_role=Disabled, 
rstp_port_state=Discarding}


# Connectivity between bridges is broken.
[root@host_1 ~]# ping -c 1 172.16.20.2
PING 172.16.20.2 (172.16.20.2) 56(84) bytes of data.
>From 172.16.20.1 icmp_seq=1 Destination Host Unreachable

--- 172.16.20.2 ping statistics ---
1 packets transmitted, 0 received, +1 errors, 100% packet loss, time 0ms

# Nothing is being transmitted on the gre tunnel
[root@host_1 ~]# tcpdump -n -i eno51
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eno51, link-type EN10MB (Ethernet), capture size 65535 bytes
^C0 packets captured
0 packets received by filter
0 packets dropped by kernel



Note: If I disable either RSTP or BFD on the above configuration, everything 
works. Only when they are both enabled things break down.



BR, Mika




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