JN0-664 Online Practice Questions

Explanation:
A sham link is a logical link between two PE routers that belong to the same OSPF area but are connected through an L3VPN. A sham link makes the PE routers appear as if they are directly connected, and prevents OSPF from preferring an intra-area back door link over the VPN backbone. A sham link creates an OSPF multihop neighborship between the PE routers using TCP port 646. The PEs exchange Type 1 OSPF LSAs instead of Type 3 OSPF LSAs for the L3VPN routes, which allows OSPF to use the correct metric for route selection1.

Explanation:
IS-IS supports two levels of routing: Level 1 (intra-area) and Level 2 (interarea). An IS-IS router can be either Level 1 only, Level 2 only, or both Level 1 and Level 2. A router that is both Level 1 and Level 2 is called a Level 1-2 router. A Level 1-2 router sends separate hello messages for each level on both point-to-point and broadcast interfaces1. A point-to-point interface provides a connection between a single source and a single destination. A broadcast interface behaves as if the router is connected to a LAN.

Explanation:
A sham link is a logical link between two PE routers that belong to the same OSPF area but are connected through an L3VPN. A sham link makes the PE routers appear as if they are directly connected, and prevents OSPF from preferring an intra-area back door link over the VPN backbone. A sham link creates an OSPF multihop neighborship between the PE routers using TCP port 646. The PEs exchange Type 1 OSPF LSAs instead of Type 3 OSPF LSAs for the L3VPN routes, which allows OSPF to use the correct metric for route selection1.

Explanation:
In the scenario described in the exhibit where R1 and R8 are not receiving each other's routes, here are three configuration commands that could potentially solve the problem, based on common BGP configurations and issues:
Configure as-override on advertisement from AS 64500 toward AS 64512.
The as-override command replaces the originating AS number with the local AS number in the AS_PATH attribute when sending BGP updates to a client in a confederation or when routes are advertised to eBGP peers in the same AS. This can be necessary when routers in different ASNs are not accepting routes due to AS path loop prevention mechanisms.
Configure remove-private on advertisements from AS 64497 toward AS 64498.
The remove-private command removes private AS numbers from the AS_PATH in BGP updates. This is often used when advertising routes to the internet, where private AS numbers should not be present. If R1 and R8 are filtering routes based on the presence of private AS numbers, this command could resolve the issue.
Configure remove-private on advertisements from AS 64500 toward AS 64499.
Similarly to the previous point, this command would remove private AS numbers from the AS_PATH when AS 64500 is advertising to AS 64499. If these routes are then being advertised to R1 and R8, and the presence of private AS numbers is causing route rejection, this could resolve the issue.

Explanation:
The information shows a Type 0 route distinguisher, which is one of the three types of route distinguishers defined by RFC 4364. A route distinguisher is a 64-bit value that is prepended to an IPv4 address to create a VPN-IPv4 address, which is unique within a VPN routing and forwarding (VRF) table. A Type 0 route distinguisher has two fields: an administrator subfield (2 bytes) and an assigned number subfield (6 bytes). The administrator subfield can be an AS number or an IP address, and the assigned number subfield can be any value assigned by the administrator. In this example, the administrator subfield is 65530 (an AS number) and the assigned number subfield is 1.