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Reference Guide for the Centillion 50/100 and Model 5000BH Switches
5-16
893-01006-C
If the link between switch 1 and switch 2 goes down (Figure 5-6), an alternate
route must be used.
Figure 5-6. Break in the IISP Network
If client A tries to set up a call to client B, but the direct link from switch 1 to
switch 2 is down, the following actions are taken to set up and deliver the call:
• Switch 1 uses its default route to client B and goes to switch 3.
• Switch 3 receives the call request and tries to send the call to switch 2.
Switch 3 discovers that the direct link to switch 2 is down.
• Switch 3 uses its default route to switch 4.
• Switch 4 receives the call request and tries to send the call to switch 2.
Switch 4 discovers that the direct link to switch 2 is down.
• Switch 4 would send the call request to switch 1, but S1/P2 and S1/P1 are in
the same link group. Call requests that come in one interface cannot be sent
out another interface that is part of the same link group. Switch 4 breaks the
IISP call routing loop by not sending the call request to switch 1.
679EA
39.01
Switch 1
Switch 3
39.03
Switch 4
39.04
39.02
Switch 2
Client B
S1/P2
S1/P3
S1/P3
S1/P1
S1/P2
S1/P2
S1/P1
S1/P2
S1/P3
S1/P2
S1/P1
S1/P1
Client A