# cat /etc/npppd/npppd.conf

/etc/npppd/npppd.conf 
tunnel PPPOE protocol pppoe {
  listen on interface cpsw0
  lcp-keepalive yes
  lcp-keepalive-interval 60
  lcp-keepalive-retry-interval 30
  lcp-keepalive-max-retries 40
  lcp-timeout 3
  debug-dump-pktin lcp

  authentication-method pap
}
authentication LOCAL type local {
    users-file "/etc/npppd/npppd-users"
}
ipcp IPCP {
    dns-servers 8.8.8.8
}

bind tunnel from PPPOE authenticated by LOCAL to pppx0

# cat /etc/hostname.cpsw0
up

# cat /etc/sysctl.conf
net.pipex.enable=1

inet 0.0.0.0 255.255.255.255 NONE \
  pppoedev cpsw0 authproto pap \
  authname '12345678@isp.net' authkey 'abcd1234' up
dest 0.0.0.1
#inet6 eui64
!/sbin/route add default -ifp pppoe0 0.0.0.1
#!/sbin/route add -inet6 default -ifp pppoe0 fe80::%pppoe0

/etc/npppd/npppd.conf:19: interface pppx0 is not found