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[lwip-users] [lwip] Question about ip_input

From: David Haas
Subject: [lwip-users] [lwip] Question about ip_input
Date: Thu, 09 Jan 2003 00:25:20 -0000 
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The following code checks if a packet is for us in ip_input:

    if(ip_addr_isany(&(netif->ip_addr)) ||
       ip_addr_cmp(&(iphdr->dest), &(netif->ip_addr)) ||
       (ip_addr_isbroadcast(&(iphdr->dest), &(netif->netmask)) &&
 ip_addr_maskcmp(&(iphdr->dest), &(netif->ip_addr), &(netif->netmask))) =
||
       ip_addr_cmp(&(iphdr->dest), IP_ADDR_BROADCAST)) {
      break;
    }

Why is one of the criteria ip_addr_isany(&(netif->ip_addr))  ?

This says that if our address is 0.0.0.0 we will take any packet and =
process it as if it is for us. A netif which has a wrongly initialized =
or configured ip address is likely to be 0.0.0.0. In fact, I think we =
should ignore any interface with address 0.0.0.0.


David Haas
NBS Card Technology
70 Eisenhower Drive,
Paramus, NJ 07652
Voice: 201-845-7373 x183
Fax: 201-845-3337
email: address@hidden

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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<META http-equiv=3DContent-Type content=3D"text/html; =
charset=3Dwindows-1252">
<META content=3D"MSHTML 6.00.2800.1126" name=3DGENERATOR>
<STYLE></STYLE>
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<BODY bgColor=3D#ffffff>
<DIV><FONT size=3D2>The following code checks if a packet is for us in=20
ip_input:</FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2>&nbsp;&nbsp;&nbsp; =
if(ip_addr_isany(&amp;(netif-&gt;ip_addr))=20
||<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =
ip_addr_cmp(&amp;(iphdr-&gt;dest),=20
&amp;(netif-&gt;ip_addr)) ||<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=20
(ip_addr_isbroadcast(&amp;(iphdr-&gt;dest), &amp;(netif-&gt;netmask))=20
&amp;&amp;<BR>&nbsp;ip_addr_maskcmp(&amp;(iphdr-&gt;dest),=20
&amp;(netif-&gt;ip_addr), &amp;(netif-&gt;netmask)))=20
||<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; =
ip_addr_cmp(&amp;(iphdr-&gt;dest),=20
IP_ADDR_BROADCAST)) {<BR>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=20
break;<BR>&nbsp;&nbsp;&nbsp; }<BR></FONT></DIV>
<DIV><FONT size=3D2>Why is one of the criteria=20
ip_addr_isany(&amp;(netif-&gt;ip_addr))&nbsp; ?</FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2>This says that if our address is 0.0.0.0 we will =
take any=20
packet and process it as if it is for us. A netif which has a wrongly=20
initialized or configured ip address is likely to be 0.0.0.0. In fact, I =
think=20
we should ignore any interface with address 0.0.0.0.</FONT></DIV>
<DIV><FONT size=3D2></FONT>&nbsp;</DIV>
<DIV><FONT size=3D2>&nbsp;</DIV></FONT>
<DIV><FONT size=3D2>David Haas<BR>NBS Card Technology<BR>70 Eisenhower=20
Drive,<BR>Paramus, NJ 07652<BR>Voice: 201-845-7373 x183<BR>Fax:=20
201-845-3337<BR>email: <A=20
href=3D"mailto:address@hidden";>address@hidden</A><BR></FONT></DIV><=
/BODY></HTML>

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