Information Technology Reference
In-Depth Information
Figure 9-7
Third-Party Next-Hop Traffic Manipulation
It would seem that ISP1 could have accepted the traffic from ISP3 at the NAP and back-
hauled it over an infrastructure link. However, this increases the size of the circuit from the
NAP router to ISP1's network. It is also a way for ISP1 to offload traffic from its backbone,
reducing the internal bandwidth needed. The end result is the use of ISP2's network as a
quasi-transit connection and bandwidth theft.
The solution to this issue is the same as with pointing default, even if the direction is
different. If ISP2 does not carry full Internet routes on the NAP router, traffic sent from
ISP3 to ISP2 for delivery to ISP1 is black-holed.
GRE Tunneling
The scenario in this section involves the use of GRE tunneling between peering routers. If
ISP1 and ISP2 are at multiple NAPs, not necessarily peering, the unethical ISP1 can build
a GRE tunnel across ISP2's network and use that tunnel as another virtual backbone link.
This is shown in Figure 9-8.
