In the IS-IS IPV6 network shown in the figure, all routers have multi-topology enabled. Configure
"ipv6 default-route-advertise always level-1" in the IS-IS processes of R4 and R5.

By default, which of the following routers have a default route in their routing table? (Multiple choice)

In the IS-IS IPv6 network shown in the figure, the interfaces of R1 and R2 both have two IPv6 addresses. Since the prefix lengths of the IPv6 addresses of R1 and R2 are different, they cannot establish a neighbor relationship.

In the OSPF network shown in the figure, R1 and R2 achieve intercommunication through Loopback0 interface through OSPF.

At the same time, R1 and R2 have enabled the MPLS LDP function, and the LDP transmission address is the IP address of the Loopback0 interface. The network engineer found that R1 and R2 could not establish an LDP session, so he first executed the command shown in the figure on R2. Based on this, which of the following reasons may cause the failure of establishing an LDP session between R1 and R2? (Multiple choice)

In the OSPF network shown in the figure, R1 and R2 achieve intercommunication through Lopback0 interface through OSPF.

At the same time, R1 and R2 have enabled the MPLS LDP function, and the LDP transmission address is the IP address of the Loopback0 interface. The network engineer found that R1 and R2 could not establish an LDP session, so he first executed the command shown in the figure on R2. Based on this, which of the following reasons may cause the failure of establishing an LDP session between R1 and R2? (Multiple choice)

The detection mechanism of BFD is that two systems establish a BFD session and periodically send BFD control messages along the path between them. If one party does not receive the BFD control message within a specified time, it is considered that a fault has occurred on the path.
Which of the following reasons will not cause the BFD session to go Down?