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Yael Ben Hur avatar Ubuntu

Can connect from one VM1 to VM2 via ssh but can't connect from VM2 to VM1 via ssh

dz flag
Yael Ben Hur

I have a networking architecture which is built like this:

  1. A virtual machine which is called UbuntuLeft
  2. A virtual machine which is called CentOS
  3. A virtual machine which is called Ubuntu right

All of the VM have an interface which is called enp0s3 which is connected to the device network.

Okay, what is your question or what do you need help with regarding this networking architecture?

Yael Ben Hur I have a networking architecture which is built like this:

  1. A virtual machine which is called Ubuntu_Left
  2. A virtual machine which is called CentOS
  3. A virtual machine which is called Ubuntu_Right

All of the VM have an interface which is called enp0s3 which is connected to the device network.

Ubuntu_Left has an interface which is called enp0s8, which creates an internal network between it and the CentOS. The IP address of that interface is: 193.168.1.1 CentOS has an interface which is called enp0s8, which creates an internal network between it and Ubuntu_Left. The IP address of that interface is: 193.168.1.2

Ubuntu_Right has an interface which is called enp0s8, which creates an internal network between it and the CentOS. The IP address of that interface is: 193.168.2.1 CentOS has an interface which is called enp0s8, which creates an internal network between it and Ubuntu_Left. The IP address of that interface is: 193.168.2.2

So the Ubuntu machines are considered in this architecture as end-devices.

I've tried connecting through ssh from each of the Ubuntus to the CentOS and it has worked. I've tried connecting through ssh from the Ubuntu_Right to the Ubuntu_Left and it worked. However, when trying to connect to Ubuntu_Right from Ubuntu_Left it doesn't work.

I debugged both of the connection and this are the results:

This the result of trying to connect with ssh from Left_Ubuntu to Right_Ubunt (which doesn't work):

OpenSSH_7.6p1 Ubuntu-4ubuntu0.7, OpenSSL 1.0.2n 7 Dec 2017
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: Connecting to 193.168.2.1 [193.168.2.1] port 22.
debug1: Connection established.
debug1: key_load_public: No such file or directory
debug1: identity file /home/username/.ssh/id_rsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/username/.ssh/id_rsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/username/.ssh/id_dsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/username/.ssh/id_dsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/username/.ssh/id_ecdsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/username/.ssh/id_ecdsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/username/.ssh/id_ed25519 type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/username/.ssh/id_ed25519-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_7.6p1 Ubuntu-4ubuntu0.7
debug1: Remote protocol version 2.0, remote software version OpenSSH_7.4
debug1: match: OpenSSH_7.4 pat OpenSSH* compat 0x04000000
debug1: Authenticating to 193.168.2.1:22 as 'username'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: curve25519-sha256
debug1: kex: host key algorithm: ecdsa-sha2-nistp256
debug1: kex: server->client cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none
debug1: kex: client->server cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ecdsa-sha2-nistp256 SHA256:t2vk80BAwRqZsX0J9Rkr3M6LB2sOLrTpNhZlodmH218
debug1: Host '193.168.2.1' is known and matches the ECDSA host key.
debug1: Found key in /home/username/.ssh/known_hosts:1
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_EXT_INFO received
debug1: kex_input_ext_info: server-sig-algs=<rsa-sha2-256,rsa-sha2-512>
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password
debug1: Next authentication method: gssapi-keyex
debug1: No valid Key exchange context
debug1: Next authentication method: gssapi-with-mic
debug1: Unspecified GSS failure. Minor code may provide more information
No Kerberos credentials available (default cache: FILE:/tmp/krb5cc_1000)

debug1: Unspecified GSS failure. Minor code may provide more information
No Kerberos credentials available (default cache: FILE:/tmp/krb5cc_1000)

debug1: Next authentication method: publickey
debug1: Trying private key: /home/username/.ssh/id_rsa
debug1: Trying private key: /home/username/.ssh/id_dsa
debug1: Trying private key: /home/username/.ssh/id_ecdsa
debug1: Trying private key: /home/username/.ssh/id_ed25519
debug1: Next authentication method: password

This the result of trying to connect with ssh from Right_Ubuntu to Left_Ubuntu (which works):

OpenSSH_7.6p1 Ubuntu-4ubuntu0.7, OpenSSL 1.0.2n 7 Dec 2017
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 19: Applying options for *
debug1: Connecting to 193.168.1.1 [193.168.1.1] port 22.
debug1: Connection established.
debug1: key_load_public: No such file or directory
debug1: identity file /home/username/.ssh/id_rsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/username/.ssh/id_rsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/username/.ssh/id_dsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/username/.ssh/id_dsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/username/.ssh/id_ecdsa type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/username/.ssh/id_ecdsa-cert type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/username/.ssh/id_ed25519 type -1
debug1: key_load_public: No such file or directory
debug1: identity file /home/username/.ssh/id_ed25519-cert type -1
debug1: Local version string SSH-2.0-OpenSSH_7.6p1 Ubuntu-4ubuntu0.7
debug1: Remote protocol version 2.0, remote software version OpenSSH_7.6p1 Ubuntu-4ubuntu0.7
debug1: match: OpenSSH_7.6p1 Ubuntu-4ubuntu0.7 pat OpenSSH* compat 0x04000000
debug1: Authenticating to 193.168.1.1:22 as 'username'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: algorithm: curve25519-sha256
debug1: kex: host key algorithm: ecdsa-sha2-nistp256
debug1: kex: server->client cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none
debug1: kex: client->server cipher: chacha20-poly1305@openssh.com MAC: <implicit> compression: none
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ecdsa-sha2-nistp256 SHA256:gGMOCOu0gP1PUAJs87KRgZizeahcpCd3hWedCRXmasU
debug1: Host '193.168.1.1' is known and matches the ECDSA host key.
debug1: Found key in /home/username/.ssh/known_hosts:1
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: rekey after 134217728 blocks
debug1: SSH2_MSG_EXT_INFO received
debug1: kex_input_ext_info: server-sig-algs=<ssh-ed25519,ssh-rsa,rsa-sha2-256,rsa-sha2-512,ssh-dss,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521>
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey,password
debug1: Next authentication method: publickey
debug1: Trying private key: /home/username/.ssh/id_rsa
debug1: Trying private key: /home/username/.ssh/id_dsa
debug1: Trying private key: /home/username/.ssh/id_ecdsa
debug1: Trying private key: /home/username/.ssh/id_ed25519
debug1: Next authentication method: password

I have noticed to major differnces between 2 debugs:

From right to left (which worked):

debug1: kex_input_ext_info: server-sig-algs=<ssh-ed25519,ssh-rsa,rsa-sha2-256,rsa-sha2-512,ssh-dss,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521>

From left to right (which didn't work):

debug1: kex_input_ext_info: server-sig-algs=<rsa-sha2-256,rsa-sha2-512>

How can I fix it?

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Saxtheowl avatar Ubuntu
iq flag
Saxtheowl

You have a ssh configuration issue on Ubuntu_Right to fix that do the following, on Ubuntu_Right open this file like this sudo nano /etc/ssh/sshd_config look for the line with PasswordAuthentication it must be like that PasswordAuthentication yes then restart the ssh server sudo systemctl restart ssh on Ubuntu_Right now it should work.

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Yael Ben Hur avatar
dz flag
Yael Ben Hur
I did it but it is still like this..
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