Allied Telesis AR2050V, Справочник по командам, Страница: 1133 / 2824

C613-50186-01 Rev B Command Reference for AR2050V 1133
AlliedWare Plus™ Operating System - Version 5.4.7-1.x
BGP
AND
BGP4+ C
OMMANDS
BGP DETERMINISTIC
-
MED
bgp deterministic-med
Overview Use this command to allow or disallow the device to compare the Multi Exit
Discriminator (MED) variable when choosing among routes advertised by different
peers in the same autonomous system (AS).
Use the bgp deterministic-med command to enable this feature to allow the
comparison of MED variables when choosing among routes advertised by
different peers in the same AS.
Use the no variant of this command to disable this feature to disallow the
comparison of the MED variable when choosing among routes advertised by
different peers in the same AS.
Syntax
bgp deterministic-med
no bgp deterministic-med
Default Disabled
Mode Router Configuration
Usage When the bgp deterministic-med command is enabled, routes from the same AS
are grouped together and ordered according to their MED values, and the best
routes of each group are compared.
The main benefit of this is that the choice of best route then does not depend on
the order in which the routes happened to be received, which is rather random and
arbitrary.
To see how this works, consider the following set of bgp table entries, all for the
same route:
If bgp deterministic-med is not enabled, then entry
3
will be chosen, because it is
an external route.
But if BGP deterministic-MED is enabled, the entries will be grouped as follows:
NOTE
: Routes from the same AS are grouped together and ordered by MED.
Entry
1
is chosen as the best route from
Group 1
, since this route has the lowest
MED value. Entry 2 has to be the best route in
Group 2
, since this is the only route
in that group. These two group winners are compared against each other, and
1: ASPATH 234, MED 120, internal, IGP metric to NEXT_HOP 40

2: ASPATH 389, MED 190, internal, IGP metric to NEXT_HOP 35

3: ASPATH 234, MED 245, external

Group 1: 1: ASPATH 234, MED 120, internal, IGP metric to NEXT_HOP 40

3: ASPATH 234, MED 245, external

Group 2: 2: ASPATH 389, MED 190, internal, IGP metric to NEXT_HOP 35
