ISIS Adjacency Configuration for Juniper Networks MX480 Routers
Question
Your company has purchased two new Juniper Networks MX480 routers. Your manager has asked you to add these two devices to the existing ISIS network.
Which two rules about ISIS adjacencies must you consider when carrying out the configuration? (Choose two)
Answers
Explanations
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A. B. C. D.AC
ISIS (Intermediate System to Intermediate System) is a routing protocol that is commonly used in large service provider networks to distribute routing information between routers. When adding new devices to an existing ISIS network, there are several rules about ISIS adjacencies that must be considered. Let's review each option:
A. For Level 1 adjacencies, area IDs must be the same: In ISIS, the network is divided into areas, similar to OSPF. Level 1 (L1) routers are within the same area, while Level 2 (L2) routers are between areas. When establishing an adjacency between two routers, the area IDs must be the same for L1 adjacencies. This is because L1 routers only have knowledge of routes within their own area, so they need to be in the same area to exchange routing information. Therefore, option A is correct.
B. For Level 2 adjacencies area IDs must be the same: Similar to option A, for L2 adjacencies, the area IDs must be the same. This is because L2 routers exchange routing information between different areas, and they need to be in the same area to do so. Therefore, option B is also correct.
C. The IS-IS levels configured on the interfaces must be the same: This statement is not entirely accurate. The ISIS level configured on each interface determines whether it is an L1 or L2 interface. However, it is not necessary for the levels configured on the interfaces to be the same for two routers to form an adjacency. For example, an L1 interface on one router can form an adjacency with an L2 interface on another router. Therefore, option C is not correct.
D. The IS-IS levels on the interfaces can be different: This statement is partially correct, as discussed in option C. The ISIS levels configured on the interfaces can be different, but it is important to note that the levels must still be compatible. For example, an L1 interface can only form an adjacency with another L1 or L1/L2 interface, while an L2 interface can only form an adjacency with another L2 or L1/L2 interface. Therefore, option D is not entirely accurate.
In conclusion, the correct answers to the question are options A and B. When adding two new Juniper Networks MX480 routers to an existing ISIS network, the area IDs must be the same for L1 and L2 adjacencies.
