[lwIP] Add NAT readme

1 files changed, 19 insertions, 0 deletions

diff --git a/components/net/lwip_nat/README.md b/components/net/lwip_nat/README.md
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index 0000000000..9672a11b54
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+++ b/components/net/lwip_nat/README.md
@@ -0,0 +1,19 @@
+lwIP NAT componenent
+
+If you want to use lwIP NAT componenent, please define LWIP_USING_NAT in rtconfig.h. 
+
+In this case the network 213.129.231.168/29 is nat'ed when packets are sent to the 
+destination network 10.0.0.0/24 (untypical example - most users will have the other 
+way around).
+
+Use following code to add a NAT entry: 
+
+  ip_nat_entry_t nat_entry;
+ 
+  nat_entry.out_if = (struct netif *)&emac_if1;
+  nat_entry.in_if = (struct netif *)&emac_if2;
+  IP4_ADDR(&nat_entry.source_net, 213, 129, 231, 168);
+  IP4_ADDR(&nat_entry.source_netmask, 255, 255, 255, 248);
+  IP4_ADDR(&nat_entry.dest_net, 10, 0, 0, 0);
+  IP4_ADDR(&nat_entry.source_netmask, 255, 0, 0, 0);
+  ip_nat_add(&_nat_entry);