JN0-664 Dumps with Practice Exam Questions Answers

The attached bit is a flag in an IS-IS LSP that indicates whether a router is connected to another area or level (L2) of the network. By default, L2 routers set this bit when they advertise their LSPs to L1 routers, and L1 routers use this bit to select a default route to reach other areas or levels through L2 routers. However, this may result in suboptimal routing if there are multiple L2 routers with different paths to other areas or levels. To ensure that L1 routers have only the most specific routes available from L2 routers, you can configure the ignore-attached-bit parameter on all L1 routers. This makes L1 routers ignore the attached bit and install all interarea routes learned from L2 routers in their routing tables.

The configuration shown in the exhibit is for a Layer 3 VPN that connects customer sites that use different AS numbers. A Layer 3 VPN is a type of VPN that uses MPLS labels to forward packets across a provider network and BGP to exchange routing information between PE routers and CE routers. A Layer 3 VPN allows customers to use different routing protocols and AS numbers at their sites, as long as they can peer with BGP at the PE-CE interface. In this example, CE-1 is using AS 65530 and CE-2 is using AS 65531, but they can still communicate through the VPN because they have BGP sessions with PE-1 and PE-2, respectively.

OSPF is an interior gateway protocol that uses link-state routing to exchange routing information among routers within a single autonomous system. OSPF prevents routing loops in multi-area networks by using two methods: area hierarchy and SPF algorithm. Area hierarchy is the concept of dividing a large OSPF network into smaller areas that are connected to a backbone area (area 0). This reduces the amount of routing information that each router has to store and process, and also limits the scope of link-state updates within each area. All areas are required to connect to area 0 either directly or through virtual links2. SPF algorithm is the method that OSPF uses to calculate the shortest path to each destination in the network based on link-state information. The SPF algorithm runs on each router and builds a shortest-path tree that represents the topology of the network from the router’s perspective. The SPF algorithm prunes looped paths within an area by choosing only one best path for each destination3.

References: 2: https://www.juniper.net/documentation/us/en/software/junos/ospf/topics/concept/ospf-area-overview.html  3: https://www.juniper.net/documentation/us/en/software/junos/ospf/topics/concept/ospf-spf-algorithm-overview.html

The sequence number is a field in the MAC mobility extended community that is used to resolve conflicting MAC address ownership claims and to help the local PE to identify the latest advertisement. The sequence number is incremented by one for every MAC address mobility event, such as when a host moves from one Ethernet segment to another segment in the EVPN network. The PE device that receives multiple MAC advertisements for the same MAC address chooses the one with the highest sequence number as the most recent and valid advertisement.

The vrf-target export parameter is used to specify one or more BGP extended community attributes that are attached to VPN routes when they are exported from a VRF routing instance to remote PE routers. This parameter allows you to control which VPN routes are accepted by remote PE routers based on their import policies. You can specify more than one vrf-target export value for a VRF routing instance to support advanced route filtering or route leaking scenarios.