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Just to make it easier to understand the topology:

http://imgur.com/GNWrMoc

Just to make it easier to understand I did some more tests today running tcpdump on the topology: compute node looking for traffic from the instance IP address. I can see traffic on all the q* and tap* interfaces:

root@stack-compute:~# ip link
...
4: ovs-system: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default
    link/ether 3a:2d:31:c4:e4:51 brd ff:ff:ff:ff:ff:ff
5: br-int: <BROADCAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN mode DEFAULT group default
    link/ether 66:e0:43:78:a2:40 brd ff:ff:ff:ff:ff:ff
7: virbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN mode DEFAULT group default
    link/ether 02:dc:94:0f:50:22 brd ff:ff:ff:ff:ff:ff
8: br-tun: <BROADCAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN mode DEFAULT group default
    link/ether ce:56:ba:46:56:47 brd ff:ff:ff:ff:ff:ff
9: qbr3c316791-b1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default
    link/ether a6:82:a3:db:9d:3e brd ff:ff:ff:ff:ff:ff
10: qvo3c316791-b1: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master ovs-system state UP mode DEFAULT group default qlen 1000
    link/ether d6:97:be:63:9c:7b brd ff:ff:ff:ff:ff:ff
11: qvb3c316791-b1: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master qbr3c316791-b1 state UP mode DEFAULT group default qlen 1000
    link/ether a6:82:a3:db:9d:3e brd ff:ff:ff:ff:ff:ff
12: tap3c316791-b1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master qbr3c316791-b1 state UNKNOWN mode DEFAULT group default qlen 500
    link/ether fe:16:3e:86:31:01 brd ff:ff:ff:ff:ff:ff

root@stack-compute:~# tcpdump -i  qbr3c316791-b1 host 172.21.21.2
tcpdump: WARNING: qbr3c316791-b1: no IPv4 address assigned
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on qbr3c316791-b1, link-type EN10MB (Ethernet), capture size 65535 bytes
15:03:01.522804 IP 172.21.21.2 > stack-compute: ICMP echo request, id 10241, seq 554, length 64
15:03:02.518428 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92
15:03:02.518436 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92
15:03:02.518442 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92
15:03:02.523860 IP 172.21.21.2 > stack-compute: ICMP echo request, id 10241, seq 555, length 64
15:03:03.525019 IP 172.21.21.2 > stack-compute: ICMP echo request, id 10241, seq 556, length 64
^C
6 packets captured
6 packets received by filter
0 packets dropped by kernel

root@stack-compute:~# tcpdump -i qvo3c316791-b1  host 172.21.21.2
tcpdump: WARNING: qvo3c316791-b1: no IPv4 address assigned
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on qvo3c316791-b1, link-type EN10MB (Ethernet), capture size 65535 bytes
15:03:35.551152 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92
15:03:35.551175 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92
15:03:35.551185 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92
15:03:35.555637 IP 172.21.21.2 > stack-compute: ICMP echo request, id 10241, seq 588, length 64
15:03:36.556769 IP 172.21.21.2 > stack-compute: ICMP echo request, id 10241, seq 589, length 64
^C
5 packets captured
6 packets received by filter
0 packets dropped by kernel

root@stack-compute:~# tcpdump -i qvb3c316791-b1  host 172.21.21.2
tcpdump: WARNING: qvb3c316791-b1: no IPv4 address assigned
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on qvb3c316791-b1, link-type EN10MB (Ethernet), capture size 65535 bytes
15:04:40.622447 IP 172.21.21.2 > stack-compute: ICMP echo request, id 10241, seq 653, length 64
15:04:41.616355 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92
15:04:41.616361 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92
15:04:41.616365 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92
15:04:41.623160 IP 172.21.21.2 > stack-compute: ICMP echo request, id 10241, seq 654, length 64
15:04:42.624099 IP 172.21.21.2 > stack-compute: ICMP echo request, id 10241, seq 655, length 64
^C
6 packets captured
6 packets received by filter
0 packets dropped by kernel

root@stack-compute:~# tcpdump -i tap3c316791-b1  host 172.21.21.2
tcpdump: WARNING: tap3c316791-b1: no IPv4 address assigned
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on tap3c316791-b1, link-type EN10MB (Ethernet), capture size 65535 bytes
15:05:22.661326 IP 172.21.21.2 > stack-compute: ICMP echo request, id 10241, seq 695, length 64
15:05:22.665548 ARP, Request who-has 172.21.21.2 tell 172.21.21.1, length 28
15:05:22.665978 ARP, Reply 172.21.21.2 is-at fa:16:3e:86:31:01 (oui Unknown), length 28
15:05:23.656582 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92
15:05:23.656601 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92
15:05:23.656609 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92
15:05:23.662462 IP 172.21.21.2 > stack-compute: ICMP echo request, id 10241, seq 696, length 64
^C
7 packets captured
8 packets received by filter
0 packets dropped by kernel

http://imgur.com/GNWrMocHowever nothing on br-int:

root@stack-compute:~# tcpdump -i br-int
tcpdump: WARNING: br-int: no IPv4 address assigned
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on br-int, link-type EN10MB (Ethernet), capture size 65535 bytes
^C
0 packets captured
0 packets received by filter
0 packets dropped by kernel

The same tests on the network node:

root@stack-network:~# ip link
...
5: ovs-system: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default
    link/ether d6:90:4c:a1:e3:d7 brd ff:ff:ff:ff:ff:ff
6: br-ex: <BROADCAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN mode DEFAULT group default
    link/ether 08:00:27:53:1c:c1 brd ff:ff:ff:ff:ff:ff
7: br-int: <BROADCAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN mode DEFAULT group default
    link/ether 96:7d:f0:b7:9d:4a brd ff:ff:ff:ff:ff:ff
9: br-tun: <BROADCAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN mode DEFAULT group default
    link/ether a6:04:a8:c5:c8:49 brd ff:ff:ff:ff:ff:ff
10: tap79ea3f6c-ec: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master ovs-system state UP mode DEFAULT group default qlen 1000
    link/ether 92:ea:69:fa:86:6d brd ff:ff:ff:ff:ff:ff
11: tap1e1f3961-b5: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master ovs-system state UP mode DEFAULT group default qlen 1000
    link/ether 2a:96:81:20:dc:66 brd ff:ff:ff:ff:ff:ff
12: tap2c8d29c1-50: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master ovs-system state UP mode DEFAULT group default qlen 1000
    link/ether 52:eb:93:36:10:b7 brd ff:ff:ff:ff:ff:ff
13: tap44a9a2ba-eb: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master ovs-system state UP mode DEFAULT group default qlen 1000
    link/ether 26:71:e6:f5:f7:60 brd ff:ff:ff:ff:ff:ff 

root@stack-network:~# tcpdump -i tap79ea3f6c-ec host 172.21.21.2
tcpdump: WARNING: tap79ea3f6c-ec: no IPv4 address assigned
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on tap79ea3f6c-ec, link-type EN10MB (Ethernet), capture size 65535 bytes
15:14:15.169006 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92
15:14:15.169025 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92
15:14:15.169032 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92
15:14:15.173283 IP 172.21.21.2 > stack-compute: ICMP echo request, id 10241, seq 1227, length 64
15:14:16.175125 IP 172.21.21.2 > stack-compute: ICMP echo request, id 10241, seq 1228, length 64
^C
5 packets captured
6 packets received by filter
0 packets dropped by kernel

root@stack-network:~# tcpdump -i tap1e1f3961-b5 host 172.21.21.2
tcpdump: WARNING: tap1e1f3961-b5: no IPv4 address assigned
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on tap1e1f3961-b5, link-type EN10MB (Ethernet), capture size 65535 bytes
^C
0 packets captured
0 packets received by filter
0 packets dropped by kernel

root@stack-network:~# tcpdump -i  tap2c8d29c1-50 host 172.21.21.2
tcpdump: WARNING: tap2c8d29c1-50: no IPv4 address assigned
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on tap2c8d29c1-50, link-type EN10MB (Ethernet), capture size 65535 bytes
^C
0 packets captured
0 packets received by filter
0 packets dropped by kernel

root@stack-network:~# tcpdump -i tap44a9a2ba-eb host 172.21.21.2
tcpdump: WARNING: tap44a9a2ba-eb: no IPv4 address assigned
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on tap44a9a2ba-eb, link-type EN10MB (Ethernet), capture size 65535 bytes
^C
0 packets captured
0 packets received by filter
0 packets dropped by kernel

root@stack-network:~# tcpdump -i br-int host 172.21.21.2
tcpdump: WARNING: br-int: no IPv4 address assigned
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on br-int, link-type EN10MB (Ethernet), capture size 65535 bytes
^C
0 packets captured
0 packets received by filter
0 packets dropped by kernel

root@stack-network:~# tcpdump -i br-ex host 172.21.21.2
tcpdump: WARNING: br-ex: no IPv4 address assigned
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on br-ex, link-type EN10MB (Ethernet), capture size 65535 bytes
^C
0 packets captured
0 packets received by filter
0 packets dropped by kernel

root@stack-network:~# tcpdump -i br-tun host 172.21.21.2
tcpdump: WARNING: br-tun: no IPv4 address assigned
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on br-tun, link-type EN10MB (Ethernet), capture size 65535 bytes
^C
0 packets captured
0 packets received by filter
0 packets dropped by kernel

Only 1 tap* interface can see any traffic.

I did some more tests today running tcpdump on just managed to fix it. The problem was caused because I was using the compute node looking same subnet for traffic from the instance IP address. I can see traffic on all the q* mgmt and tap* interfaces:br-ext external 192.168.x.x) and a separate subnet for br-tun tunneling (10.x.x.x).

root@stack-compute:~# ip link
...
4: ovs-system: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default
    link/ether 3a:2d:31:c4:e4:51 brd ff:ff:ff:ff:ff:ff
5: br-int: <BROADCAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN mode DEFAULT group default
    link/ether 66:e0:43:78:a2:40 brd ff:ff:ff:ff:ff:ff
7: virbr0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN mode DEFAULT group default
    link/ether 02:dc:94:0f:50:22 brd ff:ff:ff:ff:ff:ff
8: br-tun: <BROADCAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN mode DEFAULT group default
    link/ether ce:56:ba:46:56:47 brd ff:ff:ff:ff:ff:ff
9: qbr3c316791-b1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP mode DEFAULT group default
    link/ether a6:82:a3:db:9d:3e brd ff:ff:ff:ff:ff:ff
10: qvo3c316791-b1: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master ovs-system state UP mode DEFAULT group default qlen 1000
    link/ether d6:97:be:63:9c:7b brd ff:ff:ff:ff:ff:ff
11: qvb3c316791-b1: <BROADCAST,MULTICAST,PROMISC,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master qbr3c316791-b1 state UP mode DEFAULT group default qlen 1000
    link/ether a6:82:a3:db:9d:3e brd ff:ff:ff:ff:ff:ff
12: tap3c316791-b1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master qbr3c316791-b1 state UNKNOWN mode DEFAULT group default qlen 500
    link/ether fe:16:3e:86:31:01 brd ff:ff:ff:ff:ff:ff

root@stack-compute:~# tcpdump -i  qbr3c316791-b1 host 172.21.21.2
tcpdump: WARNING: qbr3c316791-b1: 

It seems there are no IPv4 address assigned tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on qbr3c316791-b1, link-type EN10MB (Ethernet), capture size 65535 bytes 15:03:01.522804 IP 172.21.21.2 > stack-compute: ICMP echo request, id 10241, seq 554, length 64 15:03:02.518428 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92 15:03:02.518436 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92 15:03:02.518442 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92 15:03:02.523860 IP 172.21.21.2 > stack-compute: ICMP echo request, id 10241, seq 555, length 64 15:03:03.525019 IP 172.21.21.2 > stack-compute: ICMP echo request, id 10241, seq 556, length 64 ^C 6 packets captured 6 packets received by filter 0 packets dropped by kernel root@stack-compute:~# tcpdump -i qvo3c316791-b1 host 172.21.21.2 tcpdump: WARNING: qvo3c316791-b1: no IPv4 address assigned tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on qvo3c316791-b1, link-type EN10MB (Ethernet), capture size 65535 bytes 15:03:35.551152 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92 15:03:35.551175 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92 15:03:35.551185 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92 15:03:35.555637 IP 172.21.21.2 > stack-compute: ICMP echo request, id 10241, seq 588, length 64 15:03:36.556769 IP 172.21.21.2 > stack-compute: ICMP echo request, id 10241, seq 589, length 64 ^C 5 packets captured 6 packets received by filter 0 packets dropped by kernel root@stack-compute:~# tcpdump -i qvb3c316791-b1 host 172.21.21.2 tcpdump: WARNING: qvb3c316791-b1: no IPv4 address assigned tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on qvb3c316791-b1, link-type EN10MB (Ethernet), capture size 65535 bytes 15:04:40.622447 IP 172.21.21.2 > stack-compute: ICMP echo request, id 10241, seq 653, length 64 15:04:41.616355 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92 15:04:41.616361 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92 15:04:41.616365 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92 15:04:41.623160 IP 172.21.21.2 > stack-compute: ICMP echo request, id 10241, seq 654, length 64 15:04:42.624099 IP 172.21.21.2 > stack-compute: ICMP echo request, id 10241, seq 655, length 64 ^C 6 packets captured 6 packets received by filter 0 packets dropped by kernel root@stack-compute:~# tcpdump -i tap3c316791-b1 host 172.21.21.2 tcpdump: WARNING: tap3c316791-b1: no IPv4 address assigned tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on tap3c316791-b1, link-type EN10MB (Ethernet), capture size 65535 bytes 15:05:22.661326 IP 172.21.21.2 > stack-compute: ICMP echo request, id 10241, seq 695, length 64 15:05:22.665548 ARP, Request who-has 172.21.21.2 tell 172.21.21.1, length 28 15:05:22.665978 ARP, Reply 172.21.21.2 is-at fa:16:3e:86:31:01 (oui Unknown), length 28 15:05:23.656582 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92 15:05:23.656601 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92 15:05:23.656609 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92 15:05:23.662462 IP 172.21.21.2 > stack-compute: ICMP echo request, id 10241, seq 696, length 64 ^C 7 packets captured 8 packets received by filter 0 packets dropped by kernel

However nothing on br-int:

root@stack-compute:~# tcpdump -i br-int
tcpdump: WARNING: br-int: no IPv4 address assigned
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on br-int, link-type EN10MB (Ethernet), capture size 65535 bytes
^C
0 packets captured
0 packets received by filter
0 packets dropped by kernel

The same tests way around the 3 different subnets requirement. I had to add an additional VM to act as a switch between br-ext on the network node:node and my actual router which is also on my mgmt subnet. I created a separate subnet beween them and set it up on br-ext. After that I got the instances to access the internet.

root@stack-network:~# ip link
...
5: ovs-system: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default
    link/ether d6:90:4c:a1:e3:d7 brd ff:ff:ff:ff:ff:ff
6: br-ex: <BROADCAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN mode DEFAULT group default
    link/ether 08:00:27:53:1c:c1 brd ff:ff:ff:ff:ff:ff
7: br-int: <BROADCAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN mode DEFAULT group default
    link/ether 96:7d:f0:b7:9d:4a brd ff:ff:ff:ff:ff:ff
9: br-tun: <BROADCAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UNKNOWN mode DEFAULT group default
    link/ether a6:04:a8:c5:c8:49 brd ff:ff:ff:ff:ff:ff
10: tap79ea3f6c-ec: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master ovs-system state UP mode DEFAULT group default qlen 1000
    link/ether 92:ea:69:fa:86:6d brd ff:ff:ff:ff:ff:ff
11: tap1e1f3961-b5: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master ovs-system state UP mode DEFAULT group default qlen 1000
    link/ether 2a:96:81:20:dc:66 brd ff:ff:ff:ff:ff:ff
12: tap2c8d29c1-50: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master ovs-system state UP mode DEFAULT group default qlen 1000
    link/ether 52:eb:93:36:10:b7 brd ff:ff:ff:ff:ff:ff
13: tap44a9a2ba-eb: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast master ovs-system state UP mode DEFAULT group default qlen 1000
    link/ether 26:71:e6:f5:f7:60 brd ff:ff:ff:ff:ff:ff 

root@stack-network:~# tcpdump -i tap79ea3f6c-ec host 172.21.21.2
tcpdump: WARNING: tap79ea3f6c-ec: no IPv4 address assigned
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on tap79ea3f6c-ec, link-type EN10MB (Ethernet), capture size 65535 bytes
15:14:15.169006 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92
15:14:15.169025 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92
15:14:15.169032 IP 192.168.1.201 > 172.21.21.2: ICMP host stack-compute unreachable, length 92
15:14:15.173283 IP 172.21.21.2 > stack-compute: ICMP echo request, id 10241, seq 1227, length 64
15:14:16.175125 IP 172.21.21.2 > stack-compute: ICMP echo request, id 10241, seq 1228, length 64
^C
5 packets captured
6 packets received by filter
0 packets dropped by kernel

root@stack-network:~# tcpdump -i tap1e1f3961-b5 host 172.21.21.2
tcpdump: WARNING: tap1e1f3961-b5: no IPv4 address assigned
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on tap1e1f3961-b5, link-type EN10MB (Ethernet), capture size 65535 bytes
^C
0 packets captured
0 packets received by filter
0 packets dropped by kernel

root@stack-network:~# tcpdump -i  tap2c8d29c1-50 host 172.21.21.2
tcpdump: WARNING: tap2c8d29c1-50: no IPv4 address assigned
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on tap2c8d29c1-50, link-type EN10MB (Ethernet), capture size 65535 bytes
^C
0 packets captured
0 packets received by filter
0 packets dropped by kernel

root@stack-network:~# tcpdump -i tap44a9a2ba-eb host 172.21.21.2
tcpdump: WARNING: tap44a9a2ba-eb: no IPv4 address assigned
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on tap44a9a2ba-eb, link-type EN10MB (Ethernet), capture size 65535 bytes
^C
0 packets captured
0 packets received by filter
0 packets dropped by kernel

root@stack-network:~# tcpdump -i br-int host 172.21.21.2
tcpdump: WARNING: br-int: no IPv4 address assigned
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on br-int, link-type EN10MB (Ethernet), capture size 65535 bytes
^C
0 packets captured
0 packets received by filter
0 packets dropped by kernel

root@stack-network:~# tcpdump -i br-ex host 172.21.21.2
tcpdump: WARNING: br-ex: no IPv4 address assigned
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on br-ex, link-type EN10MB (Ethernet), capture size 65535 bytes
^C
0 packets captured
0 packets received by filter
0 packets dropped by kernel

root@stack-network:~# tcpdump -i br-tun host 172.21.21.2
tcpdump: WARNING: br-tun: no IPv4 address assigned
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on br-tun, link-type EN10MB (Ethernet), capture size 65535 bytes
^C
0 packets captured
0 packets received by filter
0 packets dropped by kernel

Only 1 tap* interface can see any traffic.