Information Technology Reference
In-Depth Information
Failure and Recovery Scenarios
There are two types of failure: link failure and device failure. There are also two locations
for a failure to occur: the regional network and the core network. Both of these locations
are discussed in the next sections.
Regional Network Failure
The speed of network reconvergence around a link or device failure in the regional network
is directly related to how quickly the regional IGP can reconverge. The failure should be
seen in the core only if a portion of the network becomes disconnected and summarization
is not employed. If the network failure is large enough, it might be seen in the core if the
prefixes for an entire summary are disconnected.
When recovering from a failure, the reconvergence time should again be directly related to
the IGP reconvergence time. If the prefix must be readvertised in BGP, an additional delay
occurs as the regional core routers advertise the prefix to all the other core routers.
Core Network Failure
A link or device failure in the core should provide reconvergence at the speed at which the
core IGP reconverges. If the link between R11 and R6 fails, as shown in Figure 5-3, R11
can no longer use this link to send traffic to 10.2.0.0/16.
Figure 5-3
Physical Core Topology and Link Failure
EIGRP 102
R5
10.2.0.0/16
R7
R6
R4
EIGRP 100
R8
BGP 65100
R3
R9
R11
 
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