<html><head><meta http-equiv="Content-Type" content="text/html charset=us-ascii"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class="">
<p style="margin: 0px 0px 1em; padding: 0px; border: 0px; font-size: 15px; clear: both; color: rgb(36, 39, 41); font-family: Arial, 'Helvetica Neue', Helvetica, sans-serif;" class="">In include/linux/ip.h, </p><pre style="margin-top: 0px; padding: 5px; border: 0px; font-size: 13px; width: auto; max-height: 600px; overflow: auto; font-family: Consolas, Menlo, Monaco, 'Lucida Console', 'Liberation Mono', 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Courier New', monospace, sans-serif; background-color: rgb(239, 240, 241); word-wrap: normal; color: rgb(36, 39, 41);" class=""><code style="margin: 0px; padding: 0px; border: 0px; font-family: Consolas, Menlo, Monaco, 'Lucida Console', 'Liberation Mono', 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Courier New', monospace, sans-serif; white-space: inherit;" class="">23 static inline struct iphdr *ip_hdr(const struct sk_buff *skb)
24 {
25 return (struct iphdr *)skb_network_header(skb);
26 }
27
28 static inline struct iphdr *inner_ip_hdr(const struct sk_buff *skb)
29 {
30 return (struct iphdr *)skb_inner_network_header(skb);
31 }
32
33 static inline struct iphdr *ipip_hdr(const struct sk_buff *skb)
34 {
35 return (struct iphdr *)skb_transport_header(skb);
36 }
37 #endif /* _LINUX_IP_H */
</code></pre><p style="margin: 0px 0px 1em; padding: 0px; border: 0px; font-size: 15px; clear: both; color: rgb(36, 39, 41); font-family: Arial, 'Helvetica Neue', Helvetica, sans-serif;" class="">if I passed in sk_buff to ip_hdr and ipip_hdr</p><pre style="margin-top: 0px; padding: 5px; border: 0px; font-size: 13px; width: auto; max-height: 600px; overflow: auto; font-family: Consolas, Menlo, Monaco, 'Lucida Console', 'Liberation Mono', 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Courier New', monospace, sans-serif; background-color: rgb(239, 240, 241); word-wrap: normal; color: rgb(36, 39, 41);" class=""><code style="margin: 0px; padding: 0px; border: 0px; font-family: Consolas, Menlo, Monaco, 'Lucida Console', 'Liberation Mono', 'DejaVu Sans Mono', 'Bitstream Vera Sans Mono', 'Courier New', monospace, sans-serif; white-space: inherit;" class="">struct iphdr *ip_hdr ip_hdr_net = ip_hdr(skb);
struct iphdr *ip_hdr ip_hdr_trans = ipip_hdr(skb);
</code></pre><p style="margin: 0px 0px 1em; padding: 0px; border: 0px; font-size: 15px; clear: both; color: rgb(36, 39, 41); font-family: Arial, 'Helvetica Neue', Helvetica, sans-serif;" class="">Do ip_hdr_net->saddr and ip_hdr_trans->saddr point to the same thing? I tried it on code. It doesn't. It seems that only ip_hdr_net->saddr point to source IP address, which make sense. Because network layer has IP but not on transport layer.</p><p style="margin: 0px 0px 1em; padding: 0px; border: 0px; font-size: 15px; clear: both; color: rgb(36, 39, 41); font-family: Arial, 'Helvetica Neue', Helvetica, sans-serif;" class="">So questions:</p><p style="margin: 0px 0px 1em; padding: 0px; border: 0px; font-size: 15px; clear: both; color: rgb(36, 39, 41); font-family: Arial, 'Helvetica Neue', Helvetica, sans-serif;" class="">(1) what is differences between ip_hdr and ipip_hdr? Why we have them? No documentation whatever to figure it out.</p><p style="margin: 0px 0px 1em; padding: 0px; border: 0px; font-size: 15px; clear: both; color: rgb(36, 39, 41); font-family: Arial, 'Helvetica Neue', Helvetica, sans-serif;" class="">(2) should I use ntohX function to convert ip_hdr member data when accessing them? eg, ip_hdr_net->saddr.</p></body></html>