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Fw: Where is the edge of the Internet?

  • From: alok
  • Date: Tue Nov 05 14:50:20 2002




address (as per your scenario).  You look up the destination in the routing
table, and don't find it.  So we look in RFC792 on page 5:

      If, according to the information in the gateway's routing tables,
      the network specified in the internet destination field of a
      datagram is unreachable, e.g., the distance to the network is
      infinity, the gateway may send a destination unreachable message
      to the internet source host of the datagram.  In addition, in some
      networks, the gateway may be able to determine if the internet
      destination host is unreachable.  Gateways in these networks may
      send destination unreachable messages to the source host when the
      destination host is unreachable.


-------------> who does? the source is reachable.......via BGP.....its a
valid internet address...

And you send that to the bogus source address *HOW*?

------> how what??...it still isnt a problem for the actual traffic, the
"source" network may exist on a BGP router as being advertised from another
AS  ......but not on the edge router from where it uplinks ......as was
being discussed here

Also, note the following:

      Another case is when a datagram must be fragmented to be forwarded
      by a gateway yet the Don't Fragment flag is on.  In this case the
      gateway must discard the datagram and may return a destination
      unreachable message.

Getting Path MTU Discovery to work is tough enough without some bozo network
engineer assuming that assymetric paths with unroutable endpoint addresses
will actually work.  Yeah, sure - the destination *MIGHT* have a route back,
but if *you* don't have a route back, things will break in subtle ways.


---------------> suggest u read the thread... we were :
1. discussing a ip spoofed attacks
2. the network/ip may exist on a BGP running router as being advertised from
antoher AS/ differnet ISP.. its still present on the internet, .... but its
a BGP route, not an IGP route...although that network uplinks from ur
network...whats the problem? where does all this cause a problem? all ur
edges will 0.0.0.0/0 to some bgp running router and the packet will get
there..
......there are enuf asymmetric networks, i can assure of of that... for
one, you could simply try running a traceroute to some tracert sites from ur
PC and a reverse trace from those servers to you.... ull find lots...










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