Re: TCP/IP Packet Question

From: Rick Jones (foo_at_bar.baz.invalid)
Date: 07/26/03 

Date: Sat, 26 Jul 2003 01:26:10 GMT

Ryan Howell <tkup@insightbb.com> wrote:
> I have a question. Is it possible to send a tcp/ip packet
> accros the network without a return address?

No.

TCP segments are carried in IP datagrams, and IP datagrams have source
IP addresses in them. That is not to say that one cannot use a bogus
source IP address (modulo ISP filtering source IP addresses on the
ingress points of their networks), but running a TCP connection from a
forged IP address is a difficult thing to do. You have to be able to
either recieve or correctly guess the TCP segments that will be coming
the other way (to the bogus IP address). Not impossible, but not
necessarily trivial.

Even if you then say ditch TCP and use UDP, to get a UDP datagram to
anyone you need a valid destination IP address - either a unicast or
perhaps a multicast. That then defines a starting point (the
endpoint) for a search. Even if you put a bogus source IP address in
the IP datagram carrying the UDP datagram, someone sufficiently
motivated can still start tracing wires back from the destination
until they find the ingress point for the IP traffic.

The whole thing is rather more complicated than that, but still the
basic answer is that one cannot remain completely anonymous on the net
indefinitely so long as someone else wants badly enough to find-out.

rick jones 

-- 
oxymoron n, Hummer H2 with California Save Our Coasts and Oceans plates
these opinions are mine, all mine; HP might not want them anyway... :)
feel free to post, OR email to raj in cup.hp.com  but NOT BOTH...

Relevant Pages

  • Re: TCP/IP Packet Question
    ... accepted by the receiver) in the IP Datagram. ... > TCP segments are carried in IP datagrams, ... That is not to say that one cannot use a bogus ... > Even if you then say ditch TCP and use UDP, to get a UDP datagram to ...
    (comp.os.linux.networking)
  • Re: The beauty of TCP/IP
    ... >> On the other hand if you send a datagram and send a datagram in ... the response time depends on the number of hops. ... Datagrams are routed the same way as TCP segments, ... the round trip time for the entire packet bundle ...
    (comp.lang.java.programmer)
  • Re: Changing TCP MSS under LINUX
    ... In particular network, ... The IP datagram carrying the TCP segment has the DF bit set in the ... router is required to return an ICMP Destination Unreachable, Datagram ... to decrease send MSS so that outgoing frames fit into ...
    (comp.os.linux.networking)
  • Re: Question about UdpClient
    ... Or use a network sniffing utility like Ethereal to watch what happens on the network in each case, in case you think it's actually sending some data. ... If a datagram is sent from one end, it's received at the other end (notwithstanding the unreliable nature of UDP, of course). ... It would be a bad idea to be sending random datagrams just to test the network path, since the other end would have no way to know how to interpret such a datagram. ... The bottom line here is that calling UdpClient.Receiveisn't going to create an exception just because the remote endpoint you bound in the constructor doesn't exist, ...
    (microsoft.public.dotnet.languages.csharp)
  • Building and sending raw datagram
    ... There is a network: 192.168.0.0 ... Net configuration of "X" is: ... I would like to send a datagram from "X" to some ... (ethernet header, IP header, UDP header, data) ...
    (comp.os.linux.networking)