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I'm trying to create a configuration of 2 VMs located on the same hypervisor, to each VM I attached virtIO interface from the hypervisor by editing the XML file of each VM. I created the VMs and I got these interfaces after the attachment:

ens7: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
    inet 11.198.133.5  netmask 255.0.0.0  broadcast 11.255.255.255
    ether 00:00:11:22:33:40  txqueuelen 1000  (Ethernet)
    RX packets 147  bytes 13980 (13.6 KiB)
    RX errors 0  dropped 0  overruns 0  frame 0
    TX packets 240  bytes 17952 (17.5 KiB)
    TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

ens7: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
    inet 11.198.133.6  netmask 255.0.0.0  broadcast 11.255.255.255
    ether 00:00:11:22:33:41  txqueuelen 1000  (Ethernet)
    RX packets 57  bytes 8360 (8.1 KiB)
    RX errors 0  dropped 0  overruns 0  frame 0
    TX packets 261  bytes 18666 (18.2 KiB)
    TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

Each interface for each VM While I'm pinging from one VM to another by the IP I get the message : Destination Host Unreachable, but while pinging in one VM and running tcpdump -nei ens7 on the other one, I reciecve messages :

tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on ens7, link-type EN10MB (Ethernet), capture size 262144 bytes
12:24:49.749562 00:00:11:22:33:41 > Broadcast, ethertype ARP (0x0806), length 60: Request who-has 11.198.133.5 tell 11.198.133.6, length 46
12:24:49.749576 00:00:11:22:33:40 > 00:00:11:22:33:41, ethertype ARP (0x0806), length 42: Reply 11.198.133.5 is-at 00:00:11:22:33:40, length 28
12:24:50.773503 00:00:11:22:33:41 > Broadcast, ethertype ARP (0x0806), length 60: Request who-has 11.198.133.5 tell 11.198.133.6, length 46
12:24:50.773514 00:00:11:22:33:40 > 00:00:11:22:33:41, ethertype ARP (0x0806), length 42: Reply 11.198.133.5 is-at 00:00:11:22:33:40, length 28
12:24:51.797660 00:00:11:22:33:41 > Broadcast, ethertype ARP (0x0806), length 60: Request who-has 11.198.133.5 tell 11.198.133.6, length 46
12:24:51.797671 00:00:11:22:33:40 > 00:00:11:22:33:41, ethertype ARP (0x0806), length 42: Reply 11.198.133.5 is-at 00:00:11:22:33:40, length 28
12:24:52.821495 00:00:11:22:33:41 > Broadcast, ethertype ARP (0x0806), length 60: Request who-has 11.198.133.5 tell 11.198.133.6, length 46
12:24:52.821505 00:00:11:22:33:40 > 00:00:11:22:33:41, ethertype ARP (0x0806), length 42: Reply 11.198.133.5 is-at 00:00:11:22:33:40, length 28
12:24:53.845496 00:00:11:22:33:41 > Broadcast, ethertype ARP (0x0806), length 60: Request who-has 11.198.133.5 tell 11.198.133.6, length 46
12:24:53.845507 00:00:11:22:33:40 > 00:00:11:22:33:41, ethertype ARP (0x0806), length 42: Reply 11.198.133.5 is-at 00:00:11:22:33:40, length 28
12:24:54.869559 00:00:11:22:33:41 > Broadcast, ethertype ARP (0x0806), length 60: Request who-has 11.198.133.5 tell 11.198.133.6, length 46
12:24:54.869570 00:00:11:22:33:40 > 00:00:11:22:33:41, ethertype ARP (0x0806), length 42: Reply 11.198.133.5 is-at 00:00:11:22:33:40, length 28
12:24:55.893414 00:00:11:22:33:41 > Broadcast, ethertype ARP (0x0806), length 60: Request who-has 11.198.133.5 tell 11.198.133.6, length 46
12:24:55.893424 00:00:11:22:33:40 > 00:00:11:22:33:41, ethertype ARP (0x0806), length 42: Reply 11.198.133.5 is-at 00:00:11:22:33:40, length 28
12:24:56.917488 00:00:11:22:33:41 > Broadcast, ethertype ARP (0x0806), length 60: Request who-has 11.198.133.5 tell 11.198.133.6, length 46
12:24:56.917499 00:00:11:22:33:40 > 00:00:11:22:33:41, ethertype ARP (0x0806), length 42: Reply 11.198.133.5 is-at 00:00:11:22:33:40, length 28
12:24:57.941588 00:00:11:22:33:41 > Broadcast, ethertype ARP (0x0806), length 60: Request who-has 11.198.133.5 tell 11.198.133.6, length 46
12:24:57.941600 00:00:11:22:33:40 > 00:00:11:22:33:41, ethertype ARP (0x0806), length 42: Reply 11.198.133.5 is-at 00:00:11:22:33:40, length 28

Why doesn't the ping command work while the tcpdump recognizes the packets? I edited the XML in a way that allocates hugepages and the ovs us correct on the hypervisor.

Eran Yermiyahu
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    Are the ARP responses visible to tcpdump on **both** VMs (not just on the sender)? Your VM manager (libvirt) might have L2 packet filtering enabled. – u1686_grawity Jun 23 '22 at 10:05
  • How can I check That? There is any way to disable this? – Eran Yermiyahu Jun 23 '22 at 12:11
  • Run tcpdump on both VMs and see if they report the same packets... The important thing isn't just whether VM2 sends the ARP response, but also whether VM1 receives it. I don't know whether any of libvirt's [network filters](https://libvirt.org/formatnwfilter.html) are active by default, but it wouldn't be entirely unexpected. – u1686_grawity Jun 23 '22 at 12:19

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