Regarding the MPLS handling mode of TTL, the following description is correct?

The basic header length of an IPv6 message is a fixed value.

The means of the LAND attack is that the attacker sends an SVN packet message with the same source and destination addresses to the target host, the source port and the destination port are the same, and the receiver waits for the final ACK packet to be sent , the connection is always in a semi-connected state, resulting in a full limited TCP reception Waste of resources

In the IS-IS broadcast network type, when establishing an adjacency relationship, if the router interface priority is set to 0, it will not participate in the dis election

In an MPLS BGPVPN environment, if tags are distributed only through BGP and LDP, the MPLS tags of the message can be up to two layers of tags