Perrine@LOGICON.ARPA (Tom Perrine) (05/23/86)
This is really a dumb question, prompted by the recent comment about using ICMP redirects to tell local hosts where to send things... I get the impression that most (or at least, some) TCP/IP implementations will accept a redirect from anyone. Is this true? If so... What is to stop me (or Kevensky Gregory Breznhev) from sending a redirect to every host on my net, i.e. MILNET, indicating (for example) that they should send all of their ARPA traffic to me? My host could then copy all of the packets and forward them to the proper gateway. Talk about Big Brother, not to mention the performance impact! I am sure that I am missing something, this couldn't be true! Tom
Provan@LLL-MFE.ARPA (05/23/86)
what a happy coincident: i was just about to ask tcp-ip about this very point when the subject suddenly popped up for me! some implementations, the one i'm sending this from in fact, only apply redirects to the particular connection they apply to. for example, a redirect for a host with multiple connections from here will not cause any of the connections to change their route except the one that actually sent the redirect packet. on the other hand, i suspect there are sites that you could restrict arpanet access for by sending a redirect and then not even bothering to forward the packets. it would probably take human intervention in soem cases to get the routing entry out of the tables. CC: Perrine@LOGICON.ARPA, Tcp-ip@nic.arpa
jdreyer@BBNCCV.ARPA (Jonathan Dreyer) (05/23/86)
I got good news or bad news, depending on the answer to this question: What do hosts do when they are redirected via a "gateway" that is not on their directly-connected net? If hosts do the right thing, then most redirect pranksters won't get very far. In fact, it is hard to imagine what hosts could reasonably do besides to ignore these bogograms (and maybe complain).
MILLS@USC-ISID.ARPA.UUCP (05/23/86)
In response to the message sent 22 May 86 16:16 PDT from Perrine@LOGICON.ARPA Tom, The ICMP redirect includes a copy of the IP header (plus a few bits) of the IPgram that was received and forwarded at the gateway. Presumably, the host receiving such a thing has the opportunity to determine its authenticity using this information. Granted this doesn't nab all the bogs, especially with raw-datagram protocols, but it is much better than nothing at all. What this means is that it's hard to send gratuitous redirects to reasonable implementations that remember, at least for a little while, the address/route bindings recently used. Dave -------
gds@SRI-SPAM.ARPA.UUCP (05/23/86)
> What do hosts do when they are redirected via a "gateway" that is not > on their directly-connected net? 4.2 hosts running BBN TCP/IP ignore redirects from gateways which are not on their directly attached net. In addition, there is a notion of the "connected set of gateways" which are allowed to send redirects to the host. It starts with the "default" gateway, installed by the system manager. The default gateway may redirect the host to another gateway if there is a better route, and any other gateways put in the routing tables from similar redirects may do likewise. A gateway which has not been "installed" from previous redirects cannot redirect the host -- in fact the code is commented "Who are you, and why are you talking to us, and how do we know the IP source is not a lie?" --gregbo