简答题 What is an autonomous system？

A.It is used only for directly connected subnets or aggregate routes.
B.It can only be used with LDP.
C.It is only used when two or more labels are stacked.
D.It enables the Edge LSR to request a label pop operation from its upstream neighbors.
E.It is requested through TDP using a special label value that is also called the implicit-null value.
F.It is requested through LDP using a special label value that is also called the implicit-null value.

A.nothing，BGP automatically load-balances the traffic between different autonomous systems on all available links
B.peer between the eBGP speaker’s loopbacks， configuring eBGP multihop as required， and use an IGP to load-share between the two equal-cost paths between the loopback addresses
C.configure a loopback as update source for both EBGP peers and have on each AS an IGP to introduce two equal-cost paths to reach the EBGP peer loopback address；it is also necessary to use the next-hop-self command
D.use the ebgp-load-balance command on the neighbor statement on both sides
E.configure a loopback as update source for both EBGP peers and have on each AS an IGP to introduce two equal-cost paths to reach the peer loopback address；it is also necessary to use the ebgp-multihop and next-hop-self commands