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Re: [lwip-users] about ip_forward problem :could not allocate room for h

From: Kieran Mansley
Subject: Re: [lwip-users] about ip_forward problem :could not allocate room for header
Date: Mon, 21 Jul 2008 09:02:47 +0100

On Fri, 2008-07-18 at 20:03 +0800, WU Rui-qing wrote:

> In the pubf_header function,error occurs at line :LWIP_DEBUGF( PBUF_DEBUG | 
> 2, ("pbuf_header: failed as p < p (not enough space for new header size)\n",
> LwIP can not re-aggregate packt header in packet from PPP,and forward it by 
> ethernet interface ?

lwIP needs to move the front edge of the packet buffer to make room for
the headers. It can only do this if the packet buffer was allocated with
enough space at the start.  PPP probably has smaller headers than
Ethernet and so doesn't allocate as much space.  Normally this is not a
problem because received packets are not re-sent, but in your router you
will obviously want to do this.  You should look into where the receiver
allocates pbufs and make sure when it does so that there is enough
header space for Ethernet headers.


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