周海漢 /文

ablozhou # gmail.com

http://blog.csdn.net/ablo_zhou

2009.12.25 聖誕快樂！

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現象：

在區域網內，能ping通目標機器，並且時延是微秒級。

用ssh連區域網內其他linux機器，會等待10-30秒才有提示輸入密碼。嚴重影響工作效率。

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客戶端作業系統版本：

[email protected]:~$ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=9.10
DISTRIB_CODENAME=karmic
DISTRIB_DESCRIPTION="Ubuntu 9.10"

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除錯資訊：

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

可以看到如下的錯誤資訊：

debug1: Next authentication method: gssapi-with-mic
debug1: An invalid name was supplied
Cannot determine realm for numeric host address

事實上，正是從gssapi-with-mic這一行開始，開始耗時間。

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失敗的嘗試：

有人說是在目標機器中修改/etc/ssh/sshd_conf檔案

將UseDNS 的預設值由yes修改為no，並重啟sshd。我試了，對這種情況不管用。但不排除對別的延遲情況管用。

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有效的解決辦法：

1. 修改本地機器的hosts檔案，將目標機器的IP和域名加上去。或者讓本機的DNS 伺服器能解析目標地址。

vi /etc/hosts

192.168.12.16  ourdev

其格式是“目標機器IP 目標機器名稱”這種方法促效。沒有延遲就連上了。不過如果給每臺都加一個域名解析，挺辛苦的。但在windows下用putty或secure-crt時可以採用這種方法。

2.修改本機的客戶端配置檔案ssh_conf，注意，不是sshd_conf

vi /etc/ssh/ssh_conf

找到

GSSAPIAuthentication yes

改為

GSSAPIAuthentication no

儲存。

再連目標機器，速度就飛快了。

GSSAPI ( Generic Security Services Application Programming Interface) 是一套類似Kerberos 5 的通用網路安全系統介面。該介面是對各種不同的客戶端伺服器安全機制的封裝，以消除安全介面的不同，降低程式設計難度。但該介面在目標機器無域名解析時會有問題。我看到有人給ubuntu提交了相關bug， 說要將GSSAPIAuthentication的預設值設為no，不知為何，ubuntu9.10的預設值還是yes。

修改完畢，此時的連線除錯資料變為了：

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: