有两种方法：

1、在拨号前将默认路由删除（如果已经存在默认路由，pppd拨号是不会修改这个的，具体解释见How to hook up PPP in Linux的no default route）。

2、将ppp0设置为默认路由。

先删除原来路由，route del default

再将ppp0设置为默认路由，route add default dev ppp0

4.得到ip和dns后，关掉eth0,添加dns到/etc/resolv.conf,再用route命令添加默认网关为远端ip。

route add default gw xx.xx.xx.xx

https://blog.csdn.net/sy/column/info/yocto

https://blog.csdn.net/lqxandroid2012/article/details/

ping -I ppp0 www.baidu.com

讯享网

(1)a.ping IP:
出现 “ping: sendto: Network is unreachable”（内心崩溃。。。。。。。。）
解决方法：
[ping 不通ip解决] (http://www.cnblogs.com/embedded-linux/p/5258388.html)
测试是否ping通baidu的IP地址。如果ping不通，需要给本机加条路由，使用如下指令：

#route add default gw 10.212.18.13 route add default gw 10.212.18.13 

https://blog.csdn.net/vesamount/article/details/

ip-up脚本

之前的脚本如果没有问题，正常的话运行 pppd call gprs 就可以拨号成功，并且ifconfig后可以查看到ppp0这个网卡。但是如果你在拨号之前已经启用了以太网eth0，此时指定使用ppp0网卡ping指定ip或域名ping -I ppp0 www.baidu.com 并不能成功，原因有两个，一个是路由表中的默认网关是之前eth0生成的，一个是默认的dns服务器地址有问题。

解决默认网关问题

在pppd脚本中使能了defaultroute后，pppd会在拨号成功后向路由表中添加一条默认网关信息，但是因为之前已经有一条默认网关了，于是添加失败，默认网关依然是之前eth设置的，因此在pppd call gprs之前我们应该先route del default来删除默认路由（最好写个脚本来实现删除默认路由–拨号等一系列操作）。

讯享网ip-up脚本： #!/bin/bash #ip-up dns_file="/etc/resolv.conf" rm "$dns_file" ln /etc/ppp/resolv.conf "$dns_file" ip-down脚本 

按照ppp拨号过程中打印信息可以发现，在退出pppd进程时，会调用/etc/ppp/ip-down。因此删除默认网关，恢复dns就交由ip-down脚本做了。

#!/bin/bash #ip-down #set -vx dns_file="/etc/resolv.conf" rm $dns_file cat > "$dns_file" <<EOF # auto create by ip-down nameserver 114.114.114.114 nameserver 8.8.8.8 EOF chmod 755 "$dns_file" /etc/init.d/networking restart 

讯享网Good bay Script /usr/sbin/chat -s -v -f /etc/ppp/peers/wcdma-chat-disconnect finished (pid 759), status = 0x0 Serial link disconnected. Modem hangup # pppd call wcdma pppd options in effect: debug # (from /etc/ppp/peers/wcdma) nodetach # (from /etc/ppp/peers/wcdma) dump # (from /etc/ppp/peers/wcdma) noauth # (from /etc/ppp/peers/wcdma) user password # (from /etc/ppp/peers/wcdma) remotename 3gppp # (from /etc/ppp/peers/wcdma) /dev/ttyS5 # (from /etc/ppp/peers/wcdma) 9600 # (from /etc/ppp/peers/wcdma) lock # (from /etc/ppp/peers/wcdma) connect /usr/sbin/chat -s -v -f /etc/ppp/peers/wcdma-chat-connect # (from /etc/ppp/peers/wcdma) disconnect /usr/sbin/chat -s -v -f /etc/ppp/peers/wcdma-chat-disconnect # (from /etc/ppp/peers/wcdma) nocrtscts # (from /etc/ppp/peers/wcdma) local # (from /etc/ppp/peers/wcdma) hide-password # (from /etc/ppp/peers/wcdma) novj # (from /etc/ppp/peers/wcdma) novjccomp # (from /etc/ppp/peers/wcdma) ipcp-accept-local # (from /etc/ppp/peers/wcdma) ipcp-accept-remote # (from /etc/ppp/peers/wcdma) ipparam 3gppp # (from /etc/ppp/peers/wcdma) noipdefault # (from /etc/ppp/peers/wcdma) defaultroute # (from /etc/ppp/peers/wcdma) usepeerdns # (from /etc/ppp/peers/wcdma) noccp # (from /etc/ppp/peers/wcdma) abort on (BUSY) abort on (NO CARRIER) abort on (NO DIALTONE) abort on (ERROR) abort on (NO ANSWER) timeout set to 120 seconds send (AT^M) expect (OK) AT^M^M OK -- got it send (^MATZ^M) expect (OK) ^M ^MATZ^M^M OK -- got it send (^MAT+CGDCONT=1,"IP","3gnet",,0,0^M) expect (OK) ^M ^MAT+CGDCONT=1,"IP","3gnet",,0,0^M^M OK -- got it send (ATDT*99#^M) expect (CONNECT) ^M ATDT*99#^M^M CONNECT -- got it send (\d) Script /usr/sbin/chat -s -v -f /etc/ppp/peers/wcdma-chat-connect finished (pid 764), status = 0x0 Serial connection established. using channel 2 Using interface ppp0 Connect: ppp0 <--> /dev/ttyS5 sent [LCP ConfReq id=0x1 <asyncmap 0x0> <magic 0x6af2dcc> <pcomp> <accomp>] rcvd [LCP ConfReq id=0x1 <accomp> <pcomp> <asyncmap 0x0> <mru 1500> <magic 0x547> <auth chap MD5>] No auth is possible sent [LCP ConfRej id=0x1 <auth chap MD5>] rcvd [LCP ConfAck id=0x1 <asyncmap 0x0> <magic 0x6af2dcc> <pcomp> <accomp>] rcvd [LCP ConfReq id=0x2 <accomp> <pcomp> <asyncmap 0x0> <mru 1500> <magic 0x547>] sent [LCP ConfAck id=0x2 <accomp> <pcomp> <asyncmap 0x0> <mru 1500> <magic 0x547>] sent [IPCP ConfReq id=0x1 <addr 0.0.0.0> <ms-dns1 0.0.0.0> <ms-dns2 0.0.0.0>] rcvd [IPCP ConfNak id=0x1] sent [IPCP ConfReq id=0x2 <addr 0.0.0.0> <ms-dns1 0.0.0.0> <ms-dns2 0.0.0.0>] rcvd [IPCP ConfReq id=0x1] sent [IPCP ConfNak id=0x1 <addr 0.0.0.0>] rcvd [IPCP ConfReq id=0x2] sent [IPCP ConfAck id=0x2] rcvd [IPCP ConfNak id=0x2 <addr 10.14.221.186> <ms-dns1 219.146.1.66> <ms-dns2 219.147.1.66>] sent [IPCP ConfReq id=0x3 <addr 10.14.221.186> <ms-dns1 219.146.1.66> <ms-dns2 219.147.1.66>] rcvd [IPCP ConfAck id=0x3 <addr 10.14.221.186> <ms-dns1 219.146.1.66> <ms-dns2 219.147.1.66>] Could not determine remote IP address: defaulting to 10.64.64.64 not replacing existing default route via 192.168.99.1 local IP address 10.14.221.186 remote IP address 10.64.64.64 primary DNS address 219.146.1.66 secondary DNS address 219.147.1.66 Script /etc/ppp/ip-up started (pid 768) Script /etc/ppp/ip-up finished (pid 768), status = 0x63 

cat 4g.txt

pppd call wcdma &