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parameter of links is less than 0.1, a global cascading failure of the Internet will
emerge.
(4) An initial failure is the trigger that causes consequent cascades. Here we
focus on failure of a single AS link. We divide the initial failure as intentional
attack and random breakdown, and further analyse the survivability under these
two kinds of initial failures. We find that intentional attack causes greater effect
than random breakdown. But the effect is weakened by the automatic-restoration
process in inter-domain routing system.
2 Model for Cascading Failures in Inter-domain Routing
System
We demonstrate the cascading process in inter-domain routing system by a sim-
ple example as shown in Fig. 1. In this simple topology of ASes, the initial path
from S to D is S
D . After an initial failure happens on the link
between A and B , routers compute new routes to bypass the faulty link. Path 1,
i.e., S ₒ A ₒ C ₒ B ₒ D is chosen to carry the rerouted trac from the initial
path. However, the redistribution of trac load surpasses the capacity of link
A
A
B
C . Unlike the electrical power grids, the overload in the Internet will not lead
to breakdown of the link, but cause a congestion between A and C .Furthermore,
large amount of packets are lost. Unfortunately, the routing message in control
plane and the data trac in data plane share limited resources in BGP routers.
So sever congestion will drop the KEEPALIVE messages spoken by BGP routers
at two ends of link, and make them 'think' that the session between them is dis-
connected. Hence routers start to compute other new but less preferred route
from S to D . It turns out to be path 2, i.e., S
A
E
F
B
D .
At this time, trac is rerouted away from link A
C . The link is no longer
congested. Routers in A and C resume their BGP session automatically. And
the more preferred route - path 1 is available again. Trac is rerouted to path
1, then another round of congestion happens.
C
S
A
B
D
E
F
initial path
path 1
path 2
initial failure
congested link
Fig. 1. An example of cascading failures in inter-domain routing system
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