Re: sending a packet to another machine from a kernel module.

[Kishore A K <kishoreak@xxxxxxxxx>]

Hi,

Do you have your the subnet mask & default gateway settings on
machine 1 set correctly?? You need to receive packets on subnet
10.0.1.0 from 10.0.2.0. If not pls change the subnet mask to 
255.255.0.0 & try.

~Kishore AK

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On Fri, 4 Feb 2005 12:15:35 +0530, sridhar kumar kotturu
<sridharkumar@xxxxxxxxx> wrote:
> Iam using RHL 9, kernel vs 2.4.20-8.
> I have two machines. Machine 1 (IP 172.27.22.201) has two IP Aliases.
> 10.0.1.1 and 10.0.1.2.
> Machine 2 (IP 172.27.22.232) has a IP alias 10.0.2.1.
> (IP Alias is created using cmd #ifconfig eth0:1 10.0.0.1)
> 
>       I want to send a packet from 10.0.1.1 (m/c 1) --> 10.0.2.1 (m/c
> 2) --> 10.0.1.2 (m/c 3).
> 
> In Machine 1, Iam capturing a packet from 10.0.1.1 to 10.0.1.2 at
> netfilter hook NF_IP_LOCAL_OUT. First to send the packet to 10.0.2.1
> (m/c 2), I need to send the packet to Machine 2.
>        For sending the packet to machine 2 Iam doing the following changes
> in sk_buff structure of the packet.
> 
>        sb->dev = dev_get_by_name("eth0");
> 
>        Previously I captured the object of struct dst_entry * from a
> skbuffer of a packet going to Machine 2(for m/c 2 IP. Not to its
> alias) . Now, for the currently outgoing packet to m/c 2 IP Alias, Iam
> filling the sk_buff field struct dst_entry * with the previously
> captured dst_entry * object.
> 
>        sb->dst = my_dst_entry;  // previously captured dst_entry
> 
>  Next Iam doing the following changes in the packet Header.
> 
>        Iam adding another IP Header (i.e. IP-over-IP) with src IP 10.0.1.1
> and dst IP 10.0.2.1. Iam changing the protocol field in the outer IP
> Header to IP-over-IP value. I changed the total len field and
> calculated the new checksum.
>        Next Iam filling the MAC Header fields. src MAC as the MAC address of
> m/c 1 and dst MAC as the MAC address of m/c 2 and type of packet to
> IP.
>        Now iam returning NF_ACCEPT.
> 
>  Iam receiving the packet at machine 2. Now I captured the packet at
> netfilter-hook NF_IP_PRE_ROUTING.  Now I want to send the packet to
> 10.0.1.2 (m/c 1). For this Iam changing the sk_buff fields, outer IP
> Header fileds and MAC Header fields as before.
>        Next Iam calling the dev_queue_xmit() to send the packet to machine 1.
> 
>  Iam receiving the packet at m/c 1 netfilter hook NF_IP_PRE_ROUTING.
> But the packet is *not* reaching the Application.
>        Why it is not reaching the application ?  Whether I need to fill any
> other fields in the sk_buff structure.
>        Iam using i) ping command ii) udp sockets to send packets at the
> application layer.
> 
> Thanks n Regards,
> Sridhar.
> 
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> 
>

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