Re: Core gateway slot problem


Charles Hedrick (HEDRICK@RED.RUTGERS.EDU)
6 Apr 86 18:54:48 EST


Asymmetry in routing is quite easy to occur. In order to send a
packet from us to you, we have to know about our own local gateway, and
our local gateway has to know about some Arpanet/Milnet gateway. We
always know about our local gateway (it is hardwired in our routing
table), and I am fairly sure our gateway always knows about one of the
core gateways. This means that we can always get packets to any host
that is directly connected to the Arpanet or Milnet. In order to
respond, your host must know about an Arpanet/Milnet gateway and that
gateway must know about our local gateway. Again, you probably always
know about some Arpanet/Milnet gateway. Recently, due to various
bugs that have been discussed here enough, the Arpanet/Milnet gateways
have had a tendency to lose track of external gateways such as ours. The
result is that you can't get a packet back to us. When the core
gateways lose track of us, we can often establish connections to
machines that are directly on the Arpanet by sending them redirects
pointing to our gateway. We haven't been very successful in doing this
to sites behind a gateway. (The fact that we can do it at all is, of
course, a security problem. As far as I can tell, anybody on the
network can change around any 4.2 system's routing table in any way that
he wants.)

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