[Ns-bugs] [Bug 231] IP Address Confusion in Echo Applications

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http://www.nsnam.org/bugzilla/show_bug.cgi?id=231





------- Comment #3 from craigdo at ee.washington.edu  2008-06-24 17:49 -------
> The only reasonable option seems to be to call Packet::RemoveAllTags in the
> server before sending back the packet to the client. Patch attached.

Hmmm.  This doesn't sound like a very good solution to me.  The root of the
problem is in the socket code, not the echo server code.  I don't think it's a
good plan to have the echo server just strip off all of the tags because the
socket code doesn't deal with the tags it adds properly.

I would be very surprised to find that some random application just decided to
delete all the tags I very carefully added in my simulation.

*The* problem is that (I'll use UDP) ForwardUp creates and attaches a
SocketAddressTag to a packet and queues the packet.  RecvFrom dequeues the
packet and does a FindFirstMatchingTag but leaves the tag there.  If the packet
is forwarded to another socket, the now useless tag is left there and results
in the next ForwardUp adding a duplicate tag and RecvFrom getting the wrong
one.

No, I don't think the UDP echo server application is the right place to fix
this.  I think that ForwardUp needs to error out if it finds a SocketAddressTag
in a packet.  I think it needs to add one.  I think RecvFrom needs to find that
single tag, use it to get the address and then remove it.  

This means adding the ability to remove a tag to a packet.  It seems to me that
the simplest thing would be a RemoveFirstMatchingTag call.


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