现象
在局域网内，能ping通目标机器，并且时延是微秒级。
用ssh连局域网内其他linux机器，会等待10-30秒才有提示输入密码。严重影响工作效率。
原因
使用ssh –v，打开调试信息：
zhouhh@zhhofs:~$ ssh -v 192.168.12.16
on data /etc/ssh/ssh_config
debug1: applying options for *
debug1: connecting to 192.168.12.16 [192.168.12.16] port 22.
debug1: connection established.
debug1: identity file /home/zhouhh/.ssh/identity type -1
debug1: identity file /home/zhouhh/.ssh/id_rsa type -1
debug1: identity file /home/zhouhh/.ssh/id_dsa type -1
debug1: remote protocol version 2.0, remote software version openssh_4.3
debug1: match: openssh_4.3 pat openssh_4*
debug1: enabling compatibility mode for protocol 2.0
debug1: local version string ssh-2.0-openssh_5.1p1 debian-6ubuntu2
debug1: ssh2_msg_kexinit sent
debug1: ssh2_msg_kexinit received
debug1: kex: server->client aes128-cbc hmac-md5 none
debug1: kex: client->server aes128-cbc hmac-md5 none
debug1: ssh2_msg_kex_dh_gex_request(1024<1024<8192) sent
debug1: expecting ssh2_msg_kex_dh_gex_group
debug1: ssh2_msg_kex_dh_gex_init sent
debug1: expecting ssh2_msg_kex_dh_gex_reply
debug1: host '192.168.12.16' is known and matches the rsa host key.
debug1: found key in /home/zhouhh/.ssh/known_hosts:1
debug1: ssh_rsa_verify: signature correct
debug1: ssh2_msg_newkeys sent
debug1: expecting ssh2_msg_newkeys
debug1: ssh2_msg_newkeys received
debug1: ssh2_msg_service_request sent
debug1: ssh2_msg_service_accept received
debug1: authentications that can continue: publickey,gssapi-with-mic,password
debug1: next authentication method: gssapi-with-mic
debug1: an invalid name was supplied
cannot determine realm for numeric host address
debug1: an invalid name was supplied
cannot determine realm for numeric host address
debug1: an invalid name was supplied
debug1: next authentication method: publickey
debug1: trying private key: /home/zhouhh/.ssh/identity
debug1: trying private key: /home/zhouhh/.ssh/id_rsa
debug1: trying private key: /home/zhouhh/.ssh/id_dsa
debug1: next authentication method: password
zhouhh@192.168.12.16's password:
debug1: authentication succeeded (password).
debug1: channel 0: new [client-session]
debug1: entering interactive session.
debug1: sending environment.
debug1: sending env lang = zh_cn.utf-8
last login: fri dec 25 13:35:04 2009 from 192.168.11.146
可以看到如下的错误信息：
debug1: next authentication method: gssapi-with-mic
debug1: an invalid name was supplied
cannot determine realm for numeric host address
事实上，正是从gssapi-with-mic这一行开始，开始耗时间。
解决方法
1.修改本地机器的hosts文件，将目标机器的ip和域名加上去。或者让本机的dns 服务器能解析目标地址。
vi /etc/hosts
2.修改本机的客户端配置文件ssh_conf，注意，不是sshd_conf
vi /etc/ssh/ssh_conf
找到 gssapiauthentication yes
改为 gssapiauthentication no
保存。
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