ssh 连接很慢的解决办法

周海汉
/文

ablozhou # gmail.com
http://blog.csdn.net/ablo_zhou
2009.12.25 圣诞快乐！



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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。



========================

客户端操作系统版本：

zhouhh@zhhofs:~$ cat /etc/lsb-release

DISTRIB_ID=Ubuntu

DISTRIB_RELEASE=9.10

DISTRIB_CODENAME=karmic

DISTRIB_DESCRIPTION="Ubuntu 9.10"



========================

调试信息：

zhouhh@zhhofs:~$ ssh -v 192.168.12.16
OpenSSH_5.1p1 Debian-6ubuntu2, OpenSSL 0.9.8g 19 Oct 2007
debug1: Reading configuration 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。



====================

失败的尝试：

有人说是在目标机器中修改/etc/ssh/sshd_conf文件

将UseDNS 的缺省值由yes修改为no，并重启sshd。我试了，对这种情况不管用。但不排除对别的延迟情况管用。



====================

有效的解决办法：

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



192.168.12.16 ourdev



其格式是“目标机器IP 目标机器名称”这种方法促效。没有延迟就连上了。不过如果给每台都加一个域名解析，挺辛苦的。但在windows下用putty或secure-crt时可以采用这种方法。



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。



再连目标机器，速度就飞快了。

GSSAPI (
Generic Security Services Application Programming Interface)
是一套类似Kerberos 5 的通用网络安全系统接口。该接口是对各种不同的客户端服务器安全机制的封装，以消除安全接口的不同，降低编程难度。但该接口在目标机器无域名解析时会有问题。我看到有人给ubuntu提交了相关bug，
说要将GSSAPIAuthentication的缺省值设为no，不知为何，ubuntu9.10的缺省值还是yes。



修改完毕，此时的连接调试数据变为了：

zhouhh@zhhofs:~$ ssh -v 192.168.12.16
OpenSSH_5.1p1 Debian-6ubuntu2, OpenSSL 0.9.8g 19 Oct 2007
debug1: Reading configuration 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: 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: