I am trying to understand why an ssh server keeps dropping the connection when using openssh on Linux straight after a successful authentication, but it works fine with Filezilla in MSWindows.
The connection initially appears to succeed like so: debug2: service_accept: ssh-userauth debug1: SSH2_MSG_SERVICE_ACCEPT received debug3: send packet: type 50 debug3: receive packet: type 51 debug1: Authentications that can continue: password debug3: start over, passed a different list password debug3: preferred publickey,keyboard-interactive,password debug3: authmethod_lookup password debug3: remaining preferred: ,keyboard-interactive,password debug3: authmethod_is_enabled password debug1: Next authentication method: password user_name@server_name.com's password: debug3: send packet: type 50 debug2: we sent a password packet, wait for reply debug3: receive packet: type 52 debug1: Single to Multithread CTR cipher swap - client request debug1: Authentication succeeded (password). Authenticated to server_name.com ([123.456.78.9]:22). Then it starts renegotiating keys and it eventually fails: debug1: Final hpn_buffer_size = 2097152 debug1: HPN Disabled: 0, HPN Buffer Size: 2097152 debug1: channel 0: new [client-session] debug1: Enabled Dynamic Window Scaling debug3: ssh_session2_open: channel_new: 0 debug2: channel 0: send open debug3: ssh_packet_send2: rekex triggered debug1: enqueue packet: 90 debug3: send packet: type 20 debug1: SSH2_MSG_KEXINIT sent debug1: Entering interactive session. debug1: pledge: network debug1: rekeying in progress debug1: rekeying in progress debug3: receive packet: type 20 debug1: SSH2_MSG_KEXINIT received debug1: AUTH STATE IS 1 debug2: local client KEXINIT proposal debug2: KEX algorithms: curve25519-sha...@libssh.org,diffie-hellman-group- exchange-sha256,diffie-hellman-group14-sha1,diffie-hellman-group-exchange-sha1 debug2: host key algorithms: ssh-rsa-cert-...@openssh.com,rsa-sha2-512,rsa- sha2-256,ssh-rsa,ecdsa-sha2-nistp256-cert-...@openssh.com,ecdsa-sha2-nistp384- cert-...@openssh.com,ecdsa-sha2-nistp521-cert-...@openssh.com,ssh-ed25519- cert-...@openssh.com,ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2- nistp521,ssh-ed25519 debug2: ciphers ctos: chacha20-poly1...@openssh.com,aes256- g...@openssh.com,aes128-...@openssh.com,aes256-ctr,aes128-ctr,3des-cbc debug2: ciphers stoc: chacha20-poly1...@openssh.com,aes256- g...@openssh.com,aes128-...@openssh.com,aes256-ctr,aes128-ctr,3des-cbc debug2: MACs ctos: hmac-sha2-512-...@openssh.com,hmac-sha2-256- e...@openssh.com,umac-128-...@openssh.com,hmac-sha2-512,hmac-sha2-256,hmac- ripemd160,hmac-sha1 debug2: MACs stoc: hmac-sha2-512-...@openssh.com,hmac-sha2-256- e...@openssh.com,umac-128-...@openssh.com,hmac-sha2-512,hmac-sha2-256,hmac- ripemd160,hmac-sha1 debug2: compression ctos: none,z...@openssh.com,zlib debug2: compression stoc: none,z...@openssh.com,zlib debug2: languages ctos: debug2: languages stoc: debug2: first_kex_follows 0 debug2: reserved 0 debug2: peer server KEXINIT proposal debug2: KEX algorithms: ecdh-sha2-nistp256,ecdh-sha2-nistp384,ecdh-sha2- nistp521,diffie-hellman-group-exchange-sha256,diffie-hellman-group-exchange- sha1,diffie-hellman-group14-sha1,diffie-hellman-group1-sha1,rsa1024-sha1 debug2: host key algorithms: ssh-rsa debug2: ciphers ctos: aes256-ctr,aes192-ctr,aes128-ctr,aes256-cbc,aes192- cbc,aes128-cbc,blowfish-ctr,blowfish-cbc,cast128- cbc,arcfour256,arcfour128,3des-ctr,3des-cbc debug2: ciphers stoc: aes256-ctr,aes192-ctr,aes128-ctr,aes256-cbc,aes192- cbc,aes128-cbc,blowfish-ctr,blowfish-cbc,cast128- cbc,arcfour256,arcfour128,3des-ctr,3des-cbc debug2: MACs ctos: hmac-sha2-256,hmac-sha2-512,hmac-sha1,hmac-sha1-96,hmac- md5,hmac-md5-96,hmac-ripemd160,umac...@openssh.com debug2: MACs stoc: hmac-sha2-256,hmac-sha2-512,hmac-sha1,hmac-sha1-96,hmac- md5,hmac-md5-96,hmac-ripemd160,umac...@openssh.com debug2: compression ctos: z...@openssh.com,zlib,none debug2: compression stoc: z...@openssh.com,zlib,none debug2: languages ctos: debug2: languages stoc: debug2: first_kex_follows 0 debug2: reserved 0 debug1: kex: algorithm: diffie-hellman-group-exchange-sha256 debug1: kex: host key algorithm: ssh-rsa debug1: REQUESTED ENC.NAME is 'aes256-ctr' debug1: kex: server->client cipher: aes256-ctr MAC: hmac-sha2-512 compression: none debug1: REQUESTED ENC.NAME is 'aes256-ctr' debug1: kex: client->server cipher: aes256-ctr MAC: hmac-sha2-512 compression: none debug3: send packet: type 34 debug1: SSH2_MSG_KEX_DH_GEX_REQUEST(2048<8192<8192) sent debug1: rekeying in progress debug1: rekeying in progress debug3: receive packet: type 31 debug1: got SSH2_MSG_KEX_DH_GEX_GROUP debug2: bits set: 4105/8192 debug3: send packet: type 32 debug1: SSH2_MSG_KEX_DH_GEX_INIT sent debug1: rekeying in progress debug1: rekeying in progress debug3: receive packet: type 33 debug1: got SSH2_MSG_KEX_DH_GEX_REPLY debug1: Server host key: ssh-rsa SHA256:x0KsPBfGU/sP6+Yx1NhCoEDzF5w/IQ/6vxjuVEfPso debug2: verify_host_key: server host key RSA SHA256:x0KsPYqfxsUsP6+Yx1wKoNvRzF5w/IQ/6vxjuVEfPso matches cached key debug2: bits set: 4100/8192 debug3: send packet: type 21 debug2: set_newkeys: mode 1 debug1: set_newkeys: rekeying, input 8080 bytes 255 blocks, output 4472 bytes 0 blocks debug1: spawned a thread debug1: spawned a thread debug1: rekey after 67108864 blocks debug1: dequeue packet: 90 debug3: send packet: type 90 debug1: SSH2_MSG_NEWKEYS sent debug1: expecting SSH2_MSG_NEWKEYS debug1: rekeying in progress debug3: receive packet: type 21 debug1: SSH2_MSG_NEWKEYS received debug2: set_newkeys: mode 0 debug1: set_newkeys: rekeying, input 8096 bytes 0 blocks, output 4520 bytes 3 blocks debug1: spawned a thread debug1: spawned a thread debug1: rekey after 67108864 blocks debug3: send packet: type 1 packet_write_wait: Connection to 123.456.78.9 port 22: Broken pipe I am guessing all this respawning probably triggers some DDoS protection limit on the server and it disconnects the client. Have you observed anything similar and would you know why Linux fails, but MSWindows works as it should? PS. Setting 'RekeyLimit 15G' in ~/.ssh/config as a large enough value to avoid rekeying does not seem to work. -- Regards, Mick
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