在Internet上,用戶的域名和IP地址是一一對應的。但以虛擬撥號的方式上網,則產生了動態IP地址。這對於沒有太多錢申請域名的電腦愛好者造成了麻煩。前一段日子,由於筆者所在地區的ADSL改為虛擬撥號方式,這麻煩也困擾了筆者好一陣。經多次調試,終於實現了在Linux下動態IP地址?br>撓蛎遠趕颉O紙浼鍬枷呂矗氪蠹夜蠶恚? 之前,筆者在http://www.deerfield.com/download/dns2go/linux/index.htm為自設的服務器申請了免費域名,把dns2go放在/etc/rc.d/rc.local裡,開機即可啟動固定的免費域名。但ADSL改為虛擬撥號的方式後,沒有固定IP地址,啟動dns2go很麻煩,先用ifconfig指令查出ppp0得到的IP,再在/etc/dns2go.conf下修改IP,然後才能啟動dns2go。每次的啟動都要使用手工操作,很不方便。在沒有人的干預情況下,不能自動啟動它。寫了個C程序來解決問題,例中所有程序都假設安裝在/usr/local/bin/下,編寫個shell程序來調用C程序,目錄含有xnbh(shell程序),trans(C程序編譯後執行程序),outfile(中間臨時文件),pppoe.txt(中間文件),dns2go.conf(典型的配置文件?br>? xnbh的shell程序如下: adsl-start#啟動adls的虛擬撥號程序,ifconfig ppp0 grep -v "Link">/usr/local/bin/pppoe.txt#在目錄中產生pppoe.txt文件/usr/local/bin/trans#調用C程序提取文件pppoe.txt中的IP值,然後替換dns2go.conf中的IP值,產生中間文件outfilecp /etc/dns2go.conf /etc/dns2go.confold #備份原來的dns2go.conf文件cp /usr/local/bin/outfile /etc/dns2go.conf #替換後的dns2go.conf文件nohup /usr/local/bin/dns2go >/var/tmp/dns2go.log 2>&1 啟動固定域名 在xnbh執行第二句後產生的pppoe.txt如下: inet addr:218.65.217.109 P-t-P:172.0.0.1 Mask:255.255.255.255 UP POINTOPOINT RUNNING NOARP MULTICAST MTU:1492 Metric:1 RX packets:26 errors:0 dropped:0 overruns:0 frame:0 TX packets:27 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:3 RX bytes:1400 (1.3 Kb) TX bytes:1358 (1.3 Kb) trans.c原程序如下: #include <stdio.h> #include <ctype.h> main() { FILE *fp ,*bp,*out; int i=0; int j; char ip[16]; char dip[16]; char na[]="address="; char inip[24]; char readln [255]; char readlnn [255]; fp=fopen("/usr/local/bin/pppoe.txt","r"); if(fgets(readln,255,fp)!=NULL) {for (i=0;i<16;i++) ip=readln[20+i]; } i=0; for (i=0;i<16;i++) { if(ip!=' ') {dip=ip; printf("ip%d=%c\n",i,ip);} else{j=i; printf("j=%d",j); }} for (i=0; i<=j;i++) dip=ip; dip[j]='\0'; printf("a=%s\n",dip); fclose(fp); strcpy(inip,na); printf("inip=%s\n",inip); strcat(inip,dip); printf("inip=%s\n",inip); fp=fopen("/usr/local/bin/dns2go.conf","r"); out=fopen("/usr/local/outfile","w"); while (!feof(fp)){ if(fgets(readlnn,255,fp)!=NULL) if (strncmp("address=aaa.bbb.ccc.ddd",readlnn,15)) fputs(readlnn,out); else fputs(inip,out);} fclose(fp); fclose(out); } 在linux下用gcc –o trans trans.c編譯通過產生文件trans, dns2go.conf的配置如下: # # Simple configuration file for DNS2Go linux client # # For more information refer to the dns2go.conf manual page # # GLOBAL DIRECTIVES # # DNS2Go Server server = discovery.dns2go.com # Key (required, case-sensitive) key =aaaaaa-bbbbbb-ccccccc-ddddd(此項為申請的激活碼) # log file (optional, default: syslog) #log = /var/log/dns2go.txt # Send debug output to stdout debug # number of connection attempts (optional, default: 8) #retries = 8 # rate to send heartbeats (in minutes) (optional, default: 0=automatic) #heartbeat-rate = 0 # # DOMAIN DIRECTIVES # # Fully qualified domain name (required) domain =XXXXX.dnsgo.com(此項填寫固定免費域名) # static IP address (optional, default: external IP address) address=aaa.bbb.ccc.ddd(此項為假設IP) # online www alias redirection: choose one of the following: # (optional, default: www alias resolves to domain IP) #www-redirect-url = http://... #www-redirect-port = 8080 # offline redirect option: choose one of the following # (optional, default: offline status page) #offline-url = http://... #offline-ip = 0.0.0.0 以上xnbh程序若加入/etc/rc.d/rc.local/中則可以啟動時自動啟動固定免費域名,此時你可以啟動的apache,FTP,telnet等都可以用此免費域名了,出門在外的朋友可以很方便找到自己的服務器,熟悉shell的朋友也可以用shell完成C程序的功能,以上的程序在redhat7.2上順利通過。