Hi, I have a strange issue with a linux bridge and a openssh server running in a VM connected to that bridge. Basically when I ssh with Putty or any other windows based ssh client to an openssh server running in a centos VM connected to the external network through a linux bridge, the ssh connection hangs before the login prompt is shown. What I have learned is that when an Ethernet frame that is less then 60 bytes in size goes through the network, it is padded with 0x00 bytes until it has 60 bytes in length (64 with the frame check sequence). When this kind of padded Ethernet frame goes from the openssh server in my VM through the linux bridge to a windows host where the Putty ssh client is, the IP and TCP headers in those frames wrongly consider the 0x00 padded bytes as part of the IP / TCP user data, therefore the upstream protocol (SSH in my case) tries to interpret them, and the ssh session hangs. My understanding is that those 0x00 padded bytes are at the layer2 Ethernet frame level, and should not be considered in the user data of the higher level protocols. About the padding bytes I have found some info here: https://wiki.wireshark.org/Ethernet#Allowed_Packet_Lengths So I suspect this behavior is caused by the linux bridge, because without the linux bridge, the ssh connection works without any issue. What I mean is that if I ssh to the host operating system, the ssh connection works without any issue, however if I ssh to the centos VM that is running in that host operating system and that uses the linux bridge for external network access, then I have this behavior that I describe above. With other words, only when the linux bridge is in the path of the ssh packets, this issue happens. Now, my centos VM where I have this ssh issue is managed by libvirt, and the bridge is in forwarding mode and created by hand. If the same centos VM is migrated into an all-in-one OpenStack Pike host, where the bridge is managed by neutron, the ssh connection works again without any issue. In all cases I am talking about the latest centos openssh server, and the default ssh server configuration file. So, what do you think? Where should I look further to understand what exactly causes this behavior? Many thanks, Adrian
