Re: How to redirect the package from eth0 to eth2

[Amos Jeffries <squid3@treenet.co.nz>]

On 12/01/11 04:26, Roc Bai wrote:
 > 2011/1/11 Jan Engelhardt<jengelh@medozas.de>:
 >>
 >> On Tuesday 2011-01-11 04:22, Roc Bai wrote:
 >>>>> Dear all:
 >>>>>      in my service, there are four net card.  eth0, eth1, eth2, 
eth3. I
 >>>>> want to forward the data in from eth0 to eth1, eth2, eth3 with
 >>>>> different application protocol. Does some body send me some ideas on
 >>>>> it?
 >>>>
 >>>> If you want to re-route packages, that has to happen in pre-routing.
 >>>> If you want to use DNAT for examples, just add a rule to the
 >>>> PREROUTING chain in the nat table.
 >>>
 >>> I think the DNAT should change the package data, including the IP or
 >>> higher level protocol header, isn't it?
 >>
 >> That is the point of NAT. NAT is _not_ routing/forwarding (dammit).
 >> And it's "packet", not "package".
 >>
 >>> I think the best idea which can redirect the package is to add/change
 >>> the route rule to do it. I have write some source codes which doesn't
 >>> work.
 >>
 >> That's redundant (and as you can see, error prone). Just use
 >> the iproute utilities to define extra rules and routes, which
 >> are known to work.
 >>
 >>> ncf_get_entry() can generate a dst_entry whose dev point to the eth2
 >>> net_device structure. But when i use tcpdum -i eth2. I cannot get the
 >>> package from eth0. So it doesn't work.
 >>
 >> I don't expect it to. You are using a global variable, which is not
 >> SMP-safe without a lock.
 >> You might find Paul McKenny's Parallel Programming Book helping.
 > Jan, thanks your comments.
 > I want to make the packet ( I think it's right now:) ) redirected to
 > an anticipant port, so I haven't consider the concurrent problem now.
 >
 > In the requirement, redirect the packet with protocal is the first
 > step, and in the second step, the system should redirect the packet
 > with application packet content, such as GET in HTTP.
 >
 > eth0 ---------- if (GET in  SKB), redirect to ---------->  eth2
 >
 > So i think i have to write my module to redirect the packet now, and
 > then i can change little in the future. That's the key why i thouldn't
 > to use the exist nat/diverter tool.
 >
 > Maybe i want to know  how to set the SKB in the
 > ip_route_input_common() routine. Then the SKB can be send out from
 > eth2 port. So
 > whether my plan is right, to create a dst-entry and add it to
 > skb->_skb_refdst? and Whether the dst_entry optiosn values are
 > corrent?
 >

This discussion is showing signs of being an XYZ problem.
http://www.perlmonks.org/index.pl?node_id=542341

Roc Bai, are you attempting to do this redirection for *any* protocol? 
or just for some specific ones related to a not mentioned task?


AYJ