TCP/IP Packet sending ARP resolve

TCP/IP Packet sending ARP resolve

[cranium 2003]

 Hello sir,
                   In Linux kernel by adding debug statement i observe
that if i ping to host 10.0.0.5 with 10 packets then first i know
network stack require to resolve hosts IP to its Hardware ID by
sending ARP on Ethernet LAN. But then what i get that if i again ping
for another 10 packets to 10.0.0.5 then ARP routine is called.
               Why? Why linux kernel is not caching it. Infact its
caching i check it in debug statements then why network stack require
to resolve 10.0.0.5 host to send packets to it?

                Also i want to know once eth_header_cache called then
all successive packet to that cache host goes directly from
hh->hh_output(skb) to hard_start_xmit?
regards,
cranium