我有一个跳转盒，其中 SSH 登录到其他服务器开始出现严重延迟（长达 20 多秒）。从此跳转盒到任何目的地都会出现此问题，从不同来源登录到同一目的地不会出现相同的延迟。
下面是来自 SSH 客户端的详细输出，调试输出的延迟始终为debug1: Miscellaneous failure：
# ssh -vvv x.x.x.x
OpenSSH_5.9p1 (CentrifyDC build 4.5.3-557) (CentrifyDC build 4.5.3-557),OpenSSL 0.9.8k (CentrifyDC build 4.5.3-557) 25 Mar 2009
debug1: Reading configuration data /root/.ssh/config
debug1: /root/.ssh/config line 1: Applying options for *
debug1: Reading configuration data /etc/centrifydc/ssh/ssh_config
debug1: /etc/centrifydc/ssh/ssh_config line 52: Applying options for *
debug2: ssh_connect: needpriv 0
debug1: Connecting to x.x.x.x [x.x.x.x] port 22.
debug1: Connection established.
debug3: permantently_set_uid getpwnam(root)
debug3: getpwnam returned 0, uid = 0
debug1: permanently_set_uid: 0/0
debug3: Incorrect RSA1 identifier
debug3: Could not load "/root/.ssh/id_rsa" as a RSA1 public key
debug1: identity file /root/.ssh/id_rsa type 1
debug1: identity file /root/.ssh/id_rsa-cert type -1
debug1: Remote protocol version 2.0, remote software version OpenSSH_6.2
debug1: match: OpenSSH_6.2 pat OpenSSH*
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_5.9
debug2: fd 3 setting O_NONBLOCK
#######DELAY#######
debug1: Miscellaneous failure
No credentials cache found
#######DELAY#######
debug1: Miscellaneous failure
No credentials cache found
debug3: load_hostkeys: loading entries for host "x.x.x.x" from file "/root/.ssh/known_hosts"
debug3: load_hostkeys: found key type ECDSA in file /root/.ssh/known_hosts:36
debug3: load_hostkeys: loaded 1 keys
debug3: order_hostkeyalgs: prefer hostkeyalgs: [email protected],[email protected],[email protected],ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug2: kex_parse_kexinit: 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
debug2: kex_parse_kexinit: [email protected],[email protected],[email protected],ecdsa-sha2-nistp256,ecdsa-sha2-nistp384,ecdsa-sha2-nistp521,[email protected],[email protected],[email protected],[email protected],ssh-rsa,ssh-dss
debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,[email protected]
debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,[email protected]
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[email protected],hmac-sha2-256,hmac-sha2-256-96,hmac-sha2-512,hmac-sha2-512-96,hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: hmac-md5,hmac-sha1,[email protected],hmac-sha2-256,hmac-sha2-256-96,hmac-sha2-512,hmac-sha2-512-96,hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: none,[email protected],zlib
debug2: kex_parse_kexinit: none,[email protected],zlib
debug2: kex_parse_kexinit:
debug2: kex_parse_kexinit:
debug2: kex_parse_kexinit: first_kex_follows 0
debug2: kex_parse_kexinit: reserved 0
debug2: kex_parse_kexinit: gss-gex-sha1-toWM5Slw5Ew8Mqkay+al2g==,gss-group1-sha1-toWM5Slw5Ew8Mqkay+al2g==,gss-group14-sha1-toWM5Slw5Ew8Mqkay+al2g==,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
debug2: kex_parse_kexinit: ssh-rsa,ssh-dss,ecdsa-sha2-nistp256
debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,[email protected],[email protected],aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,[email protected]
debug2: kex_parse_kexinit: aes128-ctr,aes192-ctr,aes256-ctr,arcfour256,arcfour128,[email protected],[email protected],aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,aes192-cbc,aes256-cbc,arcfour,[email protected]
debug2: kex_parse_kexinit: [email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],hmac-md5,hmac-sha1,[email protected],[email protected],hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: [email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],[email protected],hmac-md5,hmac-sha1,[email protected],[email protected],hmac-sha2-256,hmac-sha2-512,hmac-ripemd160,[email protected],hmac-sha1-96,hmac-md5-96
debug2: kex_parse_kexinit: none,[email protected]
debug2: kex_parse_kexinit: none,[email protected]
debug2: kex_parse_kexinit:
debug2: kex_parse_kexinit:
debug2: kex_parse_kexinit: first_kex_follows 0
debug2: kex_parse_kexinit: reserved 0
debug2: mac_setup: found hmac-md5
debug1: kex: server->client aes128-ctr hmac-md5 none
debug2: mac_setup: found hmac-md5
debug1: kex: client->server aes128-ctr hmac-md5 none
debug1: sending SSH2_MSG_KEX_ECDH_INIT
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ECDSA 47:4f:f2:cb:0a:f3:47:f7:77:a4:12:d6:a8:81:21:d8
debug3: load_hostkeys: loading entries for host "x.x.x.x" from file "/root/.ssh/known_hosts"
debug3: load_hostkeys: found key type ECDSA in file /root/.ssh/known_hosts:36
debug3: load_hostkeys: loaded 1 keys
debug1: Host 'x.x.x.x' is known and matches the ECDSA host key.
debug1: Found key in /root/.ssh/known_hosts:36
debug1: ssh_ecdsa_verify: signature correct
debug2: kex_derive_keys
debug2: set_newkeys: mode 1
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug2: set_newkeys: mode 0
debug1: SSH2_MSG_NEWKEYS received
debug1: Roaming not allowed by server
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug2: service_accept: ssh-userauth
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug2: key: /root/.ssh/id_rsa (0x959db0)
debug3: input_userauth_banner
S
Kernel 3.10.0-327.10.1.el7.x86_64 on an x86_64
debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password,keyboard-interactive
debug3: start over, passed a different list publickey,gssapi-keyex,gssapi-with-mic,password,keyboard-interactive
debug3: preferred gssapi-keyex,gssapi-with-mic,publickey,keyboard-interactive,password
debug3: authmethod_lookup gssapi-keyex
debug3: remaining preferred: gssapi-with-mic,publickey,keyboard-interactive,password
debug3: authmethod_is_enabled gssapi-keyex
debug1: Next authentication method: gssapi-keyex
debug1: No valid Key exchange context
debug2: we did not send a packet, disable method
debug3: authmethod_lookup gssapi-with-mic
debug3: remaining preferred: publickey,keyboard-interactive,password
debug3: authmethod_is_enabled gssapi-with-mic
debug1: Next authentication method: gssapi-with-mic
#######DELAY#######
debug1: Miscellaneous failure
No credentials cache found
#######DELAY#######
debug1: Miscellaneous failure
No credentials cache found
debug2: we did not send a packet, disable method
debug3: authmethod_lookup publickey
debug3: remaining preferred: keyboard-interactive,password
debug3: authmethod_is_enabled publickey
debug1: Next authentication method: publickey
debug1: Offering RSA public key: /root/.ssh/id_rsa
debug3: send_pubkey_test
debug2: we sent a publickey packet, wait for reply
debug1: Server accepts key: pkalg ssh-rsa blen 279
debug2: input_userauth_pk_ok: fp 89:18:67:ee:6a:09:90:f4:9a:9e:3f:1e:b3:1f:dc:41
debug3: sign_and_send_pubkey: RSA 89:18:67:ee:6a:09:90:f4:9a:9e:3f:1e:b3:1f:dc:41
debug1: read PEM private key done: type RSA
debug1: Authentication succeeded (publickey).
Authenticated to x.x.x.x ([x.x.x.x]:22).
debug1: channel 0: new [client-session]
debug3: ssh_session2_open: channel_new: 0
debug2: channel 0: send open
debug1: Requesting [email protected]
debug1: Entering interactive session.
debug2: callback start
debug2: client_session2_setup: id 0
debug2: fd 3 setting TCP_NODELAY
debug2: channel 0: request pty-req confirm 1
debug2: channel 0: request shell confirm 1
debug2: callback done
debug2: channel 0: open confirm rwindow 0 rmax 32768
debug2: channel_input_status_confirm: type 99 id 0
debug2: PTY allocation request accepted on channel 0
debug2: channel 0: rcvd adjust 2097152
debug2: channel_input_status_confirm: type 99 id 0
debug2: shell request accepted on channel 0
Last login: Thu Nov 9 02:30:14 2017 from y.y.y.y
[[email protected] ~]#
答案1
错误消息来自 Kerberos 身份验证机制，尽管我只能猜测延迟的确切原因。
您的客户端和服务器都支持通过 GSSAPI 进行 Kerberos 身份验证。
您实际上没有 Kerberos 凭据（kinit），但客户端实际上并不知道这一点，只有 GSSAPI 机制（Kerberos）知道。因此，只要启用了 GSSAPI，客户端就会尝试使用它。
传统上，客户端的 Kerberos 依赖于反向 DNS用于确定服务器的完整域名。有时，内部 IP 地址的 rDNS 会出问题，以至于它不会简单地返回成功或失败；它根本不会返回响应，客户端被迫等待整个查询超时。（例如，ISP 或公司的 DNS 服务器可能有“保护措施”，可以完全阻止回复。）
Kerberos 可能需要知道域名才能找到正确的凭据，因此它将执行 rDNS 检查前甚至查看您是否有凭证缓存。
建议：
运行
time host x.x.x.x（其中 xxxx 是服务器的 IP 地址）并检查 DNS 解析需要多长时间。立即失败是可以的；长时间延迟是不可以的。GSSAPIAuthentication通过GSSAPIKeyExchange命令行或ssh_配置（5），暂时禁用 Kerberos。如果你知道你的网络不支持 Kerberos，请在 SSH 中禁用相同的选项服务器配置就可以完全跳过该过程。
（没有必要在双方都禁用它。如果服务器不提供它，客户端就不会尝试。）
尽管你实际上已安装我猜你会选择 Centrify SSH 而不是通常的 OpenSSH做有一个有效的 Kerberos 设置 (或者至少在某个时候有过它)，并且不是禁用它，而是考虑修复它会更好一些。