[Click] IPRewriter and ICMP packets

[Eddie Kohler]

Erik VandeKieft wrote:
>>The IPRewriter table is looked up using five properties: src addr, src port, dst
>>addr, dst port, protocol.  Note that completely different mappings might be
>>installed for different tuples.  For example you might have
>>
>>    <1.0.0.1, 20, 2.0.0.2, 30, TCP>  =>  <128.0.0.4, 929, 2.0.0.2, 30, TCP>
>>    <1.0.0.1, 40, 2.0.0.2, 59, UDP>  =>  <94.92.0.1, 40, 2.0.0.2, 59, UDP>
>>
>>Note different src addrs.
>>
>>Now an ICMP ping has three properties: source addr, dest addr, and identifier.
>>Say a ping <1.0.0.1, 2.0.0.2, 40> arrived when the IPRewriter was in the above
>>state.  How should that ping be rewritten?  Src addr 128.0.0.4 or 94.92.0.1?
> 
> 
> Hmmm. Actually, now that I think about it, I guess I could have been using
> just an IPAddrRewriter rather than an IPRewriter all this time, since I
> never translate any ports. I can always look up my mappings based on just
> the source and destination IP address.

It sounds like you want something _close_ to an IPAddrRewriter, but not quite. 
IPAddrRewriter looks at the source OR destination address -- which is what you 
want for conventional NAT.  You want an IPAddrPairRewriter that looks at source 
AND destination address.  That should be pretty easy....

> Since that doesn't look at ports, couldn't that work with ICMP ping
> packets? 

Yep.

The ICMPPingRewriter as its written still isn't enough because it
> wants a static NEWSRC and NEWDST; I at least want it to look in the table
> of an IPAddrRewriter.
> 
> Thanks! Sorry about the confusion there...
> 
> --Erik

No problem.

Eddie