Which statement is correct about IS-IS?
Which statement is correct about IS-IS?
IS-IS (Intermediate System to Intermediate System) uses areas and an autonomous system (AS). This is because IS-IS networks are structured into areas within a single AS to help in efficient routing and management. Level 1 routers operate within a single area, while Level 2 routers can route between areas, facilitating the hierarchy within the same AS.
Level 1/2 routers automatically inject a default route to the nearest Level 1 router. It's the other way around
for B to be correct, it is not the L1/L2 router who adds the default route, but the L1 router connected to based on the ATTACHED bit. "When a routing device that operates as both a Level 1 and Level 2 router (Router B) determines that it can reach at least one area other than its own (for example, in Area Y), it sets the ATTACHED bit in its Level 1 link-state PDU. Thereafter, the Level 1 router (Router A) introduces a default route pointing to the nearest attached routing device that operates as both a Level 1 and Level 2 router (Router B)." https://www.juniper.net/documentation/us/en/software/junos/is-is/topics/concept/is-is-routing-overview.html A is then the most accurate. areas. the s as multiple = 2. an AS. so single AS..
No, ISIS (Intermediate System to Intermediate System) Level 1/2 routers do not automatically inject a default route to the nearest Level 1 router.
Ans is A No, ISIS (Intermediate System to Intermediate System) Level 1/2 routers do not automatically inject a default route to the nearest Level 1 router. In ISIS, Level 1 routers only advertise their connected networks to other Level 1 routers within the same area. Level 2 routers advertise their connected networks to other Level 2 routers throughout the entire ISIS domain. When a Level 2 router receives a route from another Level 2 router, it can forward traffic to that destination directly or through a Level 1 router. If a router needs a default route, it must be manually configured or learned through some other means, such as a dynamic routing protocol like BGP (Border Gateway Protocol) or static routing. Default routes are used to forward traffic to a destination when no specific match is found in the routing table.
B is your answer here
Is the other way around: level 1 routers generate a default route to the closest level 1-2 router to reach prefixes outside of their own area. level 1-2 routers can redistribute prefixes from level 2 to level 1 so that level 1 routes can choose the most optimal path.
ISIS use area and level for peering, not AS. And L1/2 router generate default route to Level 1 is correct.
When a routing device that operates as both a Level 1 and Level 2 router determines that it can reach at least one area other than its own , it sets the ATTACHED bit in its Level 1 link-state PDU. Thereafter, the Level 1 router introduces a default route pointing to the nearest attached routing device that operates as both a Level 1 and Level 2 router. First: L1/2 router is set attached bit to its L1 PDU, if only if there is another area other than its own area. if there is only one are, it will not do it. Second: the default route is introduced by the L1 only router.
https://www.juniper.net/documentation/us/en/software/junos/is-is/topics/concept/is-is-routing-overview.html
a is correct
B https://www.juniper.net/documentation/us/en/software/junos/is-is/topics/concept/is-is-routing-overview.html
When a routing device that operates as both a Level 1 and Level 2 router (Router B) determines that it can reach at least one area other than its own (for example, in Area Y), it sets the ATTACHED bit in its Level 1 link-state PDU. Thereafter, the Level 1 router (Router A) introduces a default route pointing to the nearest attached routing device that operates as both a Level 1 and Level 2 router (Router B). [https://www.juniper.net/documentation/us/en/software/junos/is-is/topics/concept/is-is-routing-overview.html#routing-is-is-overview__d12254e173]
A An IS-IS network is a single autonomous system (AS), also called a routing domain, that consists of end systems and intermediate systems. End systems are network entities that send and receive packets. Intermediate systems send and receive packets and relay (forward) packets. (Intermediate system is the Open System Interconnection [OSI] term for a router.) ISO packets are called network PDUs. In IS-IS, a single AS can be divided into smaller groups called areas. Routing between areas is organized hierarchically, allowing a domain to be administratively divided into smaller areas. This organization is accomplished by configuring Level 1 and Level 2 intermediate systems. Level 1 systems route within an area; when the destination is outside an area, they route toward a Level 2 system. Level 2 intermediate systems route between areas and toward other ASs. No IS-IS area functions strictly as a backbone.