My debian box connect to Internet through pppoe.The ppp0 and eth0 are same card.When i run "#tcpdump -i ppp0",the output seems right.But when i run "#tcpdump -i eth0",the output is so strange:my eth0 and eth1 do not connect to any pc or LAN,eth0 connects to modem.
why there are arpa and arp packages?
8:44:31.064716 IP debian.local.mdns > 224.0.0.251.mdns: 0 PTR? 255.1.168.192.in-addr.arpa. (44)
18:44:31.353219 arp who-has 192.168.1.137 tell 192.168.1.1
18:44:32.068634 IP debian.local.mdns > 224.0.0.251.mdns: 0 PTR? 255.1.168.192.in-addr.arpa. (44)
18:44:32.355026 arp who-has 192.168.1.137 tell 192.168.1.1
18:44:34.072341 IP debian.local.mdns > 224.0.0.251.mdns: 0 PTR? 255.1.168.192.in-addr.arpa. (44)

15:10:09.969835 arp who-has 119.4.47.2 tell 192.168.1.57
15:10:09.971860 arp who-has 119.4.47.2 tell 192.168.1.57
15:10:09.973822 arp who-has 119.4.47.2 tell 192.168.1.57
15:10:09.975761 arp who-has 119.4.47.2 tell 192.168.1.57
15:10:09.977690 arp who-has 119.4.47.2 tell 192.168.1.57
15:10:09.979220 arp who-has 119.4.47.2 tell 119.4.47.2
15:10:09.981949 arp who-has 119.4.47.2 tell 119.4.47.2
15:10:09.983880 arp who-has 119.4.47.2 tell 119.4.47.2

This is my /etc/network/interfaces
# The loopback network interface
auto lo
iface lo inet loopback

# The primary network interface
allow-hotplug eth0
iface eth0 inet static
address 192.168.0.50
netmask 255.255.255.0
network 192.168.0.0
broadcast 192.168.0.255
# dns-* options are implemented by the resolvconf package, if installed
#dns-nameservers 192.168.1.50
#dns-search crazyfrog.com

#added by myself
allow-hotplug eth1
iface eth1 inet static
address 192.168.1.100
netmask 255.255.255.0
network 192.168.1.0
broadcast 192.168.1.255
#if dhcp
#auto eth1
#iface eth1 inet dhcp

auto dsl-provider
iface dsl-provider inet ppp
pre-up /sbin/ifconfig eth0 up # line maintained by pppoeconf
provider dsl-provider

auto eth0