Hi,

I have seen this issue consistently.

I freshly install Ubuntu 14.04 onto Cisco UCS and use devstack to deploy 
OpenStack (stable Juno) to make it a Compute node.

For the very first VM launched at this node, it won’t respond to ARP request (I 
ping from the router namespace).

The Linux bridge tap interface shows it’s sending packets to the VM, and 
tcpdump confirms it.


qbr8a29c673-4f Link encap:Ethernet  HWaddr b2:76:d7:47:c2:fe

          inet6 addr: fe80::98ac:73ff:fea8:8be1/64 Scope:Link

          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

          RX packets:1137 errors:0 dropped:0 overruns:0 frame:0

          TX packets:8 errors:0 dropped:0 overruns:0 carrier:0

          collisions:0 txqueuelen:0

          RX bytes:49528 (49.5 KB)  TX bytes:648 (648.0 B)


qvb8a29c673-4f Link encap:Ethernet  HWaddr b2:76:d7:47:c2:fe

          inet6 addr: fe80::b076:d7ff:fe47:c2fe/64 Scope:Link

          UP BROADCAST RUNNING PROMISC MULTICAST  MTU:1500  Metric:1

          RX packets:1132 errors:0 dropped:0 overruns:0 frame:0

          TX packets:22 errors:0 dropped:0 overruns:0 carrier:0

          collisions:0 txqueuelen:1000

          RX bytes:63592 (63.5 KB)  TX bytes:3228 (3.2 KB)


qvo8a29c673-4f Link encap:Ethernet  HWaddr 9a:2b:5e:e4:22:f9

          inet6 addr: fe80::982b:5eff:fee4:22f9/64 Scope:Link

          UP BROADCAST RUNNING PROMISC MULTICAST  MTU:1500  Metric:1

          RX packets:22 errors:0 dropped:0 overruns:0 frame:0

          TX packets:1132 errors:0 dropped:0 overruns:0 carrier:0

          collisions:0 txqueuelen:1000

          RX bytes:3228 (3.2 KB)  TX bytes:63592 (63.5 KB)


tap8a29c673-4f Link encap:Ethernet  HWaddr fe:16:3e:12:49:10

          inet6 addr: fe80::fc16:3eff:fe12:4910/64 Scope:Link

          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

          RX packets:7 errors:0 dropped:0 overruns:0 frame:0

          TX packets:1143 errors:0 dropped:0 overruns:0 carrier:0

          collisions:0 txqueuelen:500

          RX bytes:2022 (2.0 KB)  TX bytes:64490 (64.4 KB)



localadmin@qa6:~/devstack$ ifconfig tap8a29c673-4f

tap8a29c673-4f Link encap:Ethernet  HWaddr fe:16:3e:12:49:10

          inet6 addr: fe80::fc16:3eff:fe12:4910/64 Scope:Link

          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

          RX packets:7 errors:0 dropped:0 overruns:0 frame:0

          TX packets:1236 errors:0 dropped:0 overruns:0 carrier:0

          collisions:0 txqueuelen:500

          RX bytes:2022 (2.0 KB)  TX bytes:69698 (69.6 KB)


localadmin@qa6:~/devstack$ ifconfig tap8a29c673-4f

tap8a29c673-4f Link encap:Ethernet  HWaddr fe:16:3e:12:49:10

          inet6 addr: fe80::fc16:3eff:fe12:4910/64 Scope:Link

          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

          RX packets:7 errors:0 dropped:0 overruns:0 frame:0

          TX packets:1239 errors:0 dropped:0 overruns:0 carrier:0

          collisions:0 txqueuelen:500

          RX bytes:2022 (2.0 KB)  TX bytes:69866 (69.8 KB)


localadmin@qa6:~/devstack$ sudo tcpdump -i tap8a29c673-4f

tcpdump: WARNING: tap8a29c673-4f: no IPv4 address assigned

tcpdump: verbose output suppressed, use -v or -vv for full protocol decode

listening on tap8a29c673-4f, link-type EN10MB (Ethernet), capture size 65535 
bytes

13:07:31.678751 ARP, Request who-has 10.0.0.14 tell 10.0.0.1, length 42

13:07:32.678813 ARP, Request who-has 10.0.0.14 tell 10.0.0.1, length 42

13:07:32.678838 ARP, Request who-has 10.0.0.14 tell 10.0.0.1, length 42

13:07:33.678778 ARP, Request who-has 10.0.0.14 tell 10.0.0.1, length 42

13:07:34.678840 ARP, Request who-has 10.0.0.14 tell 10.0.0.1, length 42



Usually I would reboot the VM and the ping works fine afterwards.


localadmin@qa6:~/devstack$ sudo tcpdump -i tap8a29c673-4f

tcpdump: WARNING: tap8a29c673-4f: no IPv4 address assigned

tcpdump: verbose output suppressed, use -v or -vv for full protocol decode

listening on tap8a29c673-4f, link-type EN10MB (Ethernet), capture size 65535 
bytes

13:13:18.154711 IP 10.0.0.1 > 10.0.0.14: ICMP echo request, id 25711, seq 32, 
length 64

13:13:18.154996 IP 10.0.0.14 > 10.0.0.1: ICMP echo reply, id 25711, seq 32, 
length 64

13:13:19.156244 IP 10.0.0.1 > 10.0.0.14: ICMP echo request, id 25711, seq 33, 
length 64

13:13:19.156502 IP 10.0.0.14 > 10.0.0.1: ICMP echo reply, id 25711, seq 33, 
length 64


Looking for suggestions on how to debug this issue?


Thanks,

Danny
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