A router has two paths to reach another network in a different autonomous system. Neither
route was generated by the local router and both routes have the same default weight and
local preference values. Which statement is true about how BGP would select the best path?

A.
To influence one route to be preferred, its default local preference value will be changed
via the use of the command bgp default local-preference 50.

B.
The router will prefer the shortest autonomous system path.

C.
If the command bgp always-compare-med has been given, then the router will prefer the
route with the highest MED.

D.
The router will prefer the route with the lower MED.

Explanation:
The shortest AS path is the fourth item checked by BGP routers, while the MED values are
one of the last items looked at by BGP routers. The following is a partial list of rules used by
BGP to determine the best path.
1. Prefer the path with the highest WEIGHT.
Note: WEIGHT is a Cisco-specific parameter, local to the router on which it’s configured.
2. Prefer the path with the highest LOCAL_PREF.
3. Prefer the path that was locally originated via a network or aggregate BGP
subcommand, or through redistribution from an IGP. Local paths sourced by network or
redistribute commands are preferred over local aggregates sourced by the aggregateaddress command.
4. Prefer the path with the shortest AS_PATH. Note the following:
5. Prefer the path with the lowest origin type: IGP is lower than EGP, and EGP is lower
than INCOMPLETE.
6. Prefer the path with the lowest multi-exit discriminator (MED).

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094431.shtml