11.4 Usage Examples

11.4 Usage Examples

Applications that are supposed to be used in end hosts such as telnet, ftp, and ssh may not explicitly support the notion of address scope, especially of link-local addresses. However, an expert user (e.g., a network administrator) sometimes has to give even link-local addresses to such applications.

Here is a concrete example. Consider a multi-linked router called "R1" that has at least two point-to-point interfaces (links). Each of the interfaces is connected to another router, "R2" and "R3", respectively. Also assume that the point-to-point interfaces have link-local addresses only.

Now suppose that the routing system on R2 hangs up and has to be reinvoked. In this situation, we may not be able to use a global address of R2, because this is routing trouble and we cannot expect to have enough routes for global reachability to R2.

Hence, we have to login R1 first and then try to login R2 by using link-local addresses. In this case, we have to give the link-local address of R2 to, for example, telnet. Here we assume the address is fe80::2.

Note that we cannot just type

% telnet fe80::2

here, since R1 has more than one link and hence the telnet command cannot detect which link it should try to use for connecting. Instead, we should type the link-local address with the link index as follows:

% telnet fe80::2%3

where "3" after the delimiter character % corresponds to the link index of the point-to-point link.