Administrator Guide

One AS assigns the MED a value and the other AS uses that value to decide the preferred path. For this
example, assume the MED is the only attribute applied. In the following illustration, AS100 and AS200 connect
in two places. Each connection is a BGP session. AS200 sets the MED for its T1 exit point to 100 and the MED
for its OC3 exit point to 50. This sets up a path preference through the OC3 link. The MEDs are advertised to
AS100 routers so they know which is the preferred path.
MEDs are non-transitive attributes. If AS100 sends an MED to AS200, AS200 does not pass it on to AS300 or
AS400. The MED is a locally relevant attribute to the two participating ASs (AS100 and AS200).
NOTE: The MEDs are advertised across both links, so if a link goes down, AS 1 still has connectivity to
AS300 and AS400.
Figure 23. Multi-Exit Discriminators
NOTE: With the Dell Networking OS version 8.3.1.0, configuring the set metric-type internal
command in a route-map advertises the IGP cost as MED to outbound EBGP peers when redistributing
routes. The configured set metric value overwrites the default IGP cost.
Origin
The origin indicates the origin of the prefix, or how the prefix came into BGP. There are three origin codes:
IGP, EGP, INCOMPLETE.
Origin Type Description
IGP Indicates the prefix originated from information learned through an interior gateway
protocol.
EGP Indicates the prefix originated from information learned from an EGP protocol, which
NGP replaced.
INCOMPLETE Indicates that the prefix originated from an unknown source.
Border Gateway Protocol IPv4 (BGPv4) 205