Hi, I have a strange issue in a libvirt environment, and I do not know how to solve it. I have two centos hosts: first one is a physical server called server1, that acts as a host for the second one, called centos1. The centos1 is a virtual machine (VM) running in server1. A linux bridge in forwarding mode is used to connect the centos1 VM network interface to the server1 network interface and to the external network. The centos1 VM and the linux bridge are managed with libvirt (well, the bridge itself in this case is created manually). # virsh net-dumpxml br0 <network connections='1'> <name>br0</name> <uuid>5aaf72a5-023d-4b84-9d7c-d68b0918f620</uuid> <forward mode='bridge'/> <bridge name='br0'/> </network> # brctl show bridge name bridge id STP enabled interfaces br0 8000.fc15b4137688 no eno1 vnet0 Both server1 and centos1 have IP addresses in the same subnet, and both are reachable with ping from every other host in my network. In both server1 and centos1, the openssh-server configuration in /etc/ssh/sshd_config is the default one, and has not been changed. When I ssh with Putty to the physical server server1 IP address, everything works as expected: I get a login prompt, I enter my password and I log in. However, when I use Putty to connect to the centos1 VM, I do not get a login prompt whatsoever. So I think there might be some issue in between the server1 physical interface and my centos VM. I used openssh-server in debug mode, so see where the ssh connection hangs, and here is what I get: [...] debug1: Server will not fork when running in debugging mode. debug1: rexec start in 5 out 5 newsock 5 pipe -1 sock 8 debug1: sshd version OpenSSH_7.4, OpenSSL 1.0.2k-fips 26 Jan 2017 debug1: private host key #0: ssh-rsa SHA256:pEuFQsodwK+0PoRzbVRba1ahHLEpwp8DG2KGQmxOGJk debug1: private host key #1: ecdsa-sha2-nistp256 SHA256:F6HrSNWZhYaU7LMweI+RBviqTCHcTYyMBGPDz5OjT4c debug1: private host key #2: ssh-ed25519 SHA256:aG3V6jjPHXUnNeavbxT/xozqrb5q3yWDkkAmXBCdnGk debug1: inetd sockets after dupping: 3, 3 Connection from x.x.x.181 port 49436 on x.x.x.115 port 22 debug1: Client protocol version 2.0; client software version PuTTY_Release_0.70 debug1: no match: PuTTY_Release_0.70 debug1: Local version string SSH-2.0-OpenSSH_7.4 debug1: Enabling compatibility mode for protocol 2.0 debug1: SELinux support enabled [preauth] debug1: permanently_set_uid: 74/74 [preauth] debug1: list_hostkey_types: ssh-rsa,rsa-sha2-512,rsa-sha2-256,ecdsa-sha2-nistp256,ssh-ed25519 [preauth] debug1: SSH2_MSG_KEXINIT sent [preauth] I tried with other windows based ssh clients (MobaXterm) and the same issue happens. I discussed this with people in the openssh mailing list, and they said this issue could most probably be caused by a path MTU/fragmentation problem... Then I moved my centos1 qcow2 image in another physical server called server2, with exactly the same hw specs and network connections, where I have installed an all-in-one OpenStack Pike. The network would be managed with neutron in this case, however I have configured neutron exactly so that the centos1 VM interface connects through a linux bridge (managed by neutron) to the server1 physical network interface, like in the libvirt case. # brctl show bridge name bridge id STP enabled interfaces brqa13eec69-a4 8000.0e7faabad6d4 no eno1 tap8cb53db0-fb tapb24a1cc5-20 Above the tapb24a1cc5-20 is the tap interface towards my centos1 VM. In this case, the Putty issue is gone, and I do not have any issue anymore. If I go back to the libvirt environment in server1, I get the same issue again. So I tend to think that my ssh connection issue is caused by the libvirt and the way networking is configured, however I do not know how to troubleshoot this further anymore. Any help is greatly appreciated. Adrian