Routers R1, R2, R3, and R4 are running IS-IS. Assuming all interfaces are added to IS-IS as point-to-point and no commands are issued at the interface level to restrict adjacencies, which of the following statements is TRUE?
A.
Routers R1 and R2 are L2 routers. Routers R3 and R4 are L1 routers.
B.
Routers R1 and R2 are L2 routers. Routers R3 and R4 are L1/L2 routers.
C.
Routers R1 and R2 are L1/L2 routers. Routers R3 and R4 are L1 routers.
From the output, we can see that theusagecolumn indicates whether a router is operating as an L1 or L2 router:
RoutersR1andR2have a usage ofL2, meaning they are L2 routers.
RoutersR3andR4have a usage ofL1, meaning they are L1 routers.
TheL1/L2designations refer to whether the routers participate in both Level 1 and Level 2 of IS-IS:
L1 routersonly communicate within their own area.
L2 routerscommunicate between areas.
In this case,R1andR2are L2 routers, andR3andR4are L1 routers.
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RoutersR1andR2have a usage ofL2, meaning they are L2 routers.
RoutersR3andR4have a usage ofL1, meaning they are L1 routers.
L1 routersonly communicate within their own area.
L2 routerscommunicate between areas.
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