BGP MED preference (0 vs NULL)

Answered Question
Feb 15th, 2010
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Hi

Does anyone know what's cisco's preference when dealing with a path that has a MED set to 0 and a path that does not have a MED set (assuming everything else is default)?


Thank you,


Tom

Correct Answer by Peter Paluch about 7 years 5 months ago

Tomek,


As far as I know, this depends on the setting of the BGP process.


By default, if the MED attribute is missing, the IOS assigns the value of 0 to the route. You can change this behavior using the command bgp bestpath med missing-as-worst in which case the missing MED attribute will be internally assigned the value of 4294967294.


You may want to read the following link to the command reference:


http://www.cisco.com/en/US/partner/docs/ios/iproute/command/reference/irp_bgp1.html#wp1012195


Also, this document may be very interesting to read:


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


Best regards,

Peter

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Correct Answer
Peter Paluch Mon, 02/15/2010 - 14:00
User Badges:
  • Cisco Employee,

Tomek,


As far as I know, this depends on the setting of the BGP process.


By default, if the MED attribute is missing, the IOS assigns the value of 0 to the route. You can change this behavior using the command bgp bestpath med missing-as-worst in which case the missing MED attribute will be internally assigned the value of 4294967294.


You may want to read the following link to the command reference:


http://www.cisco.com/en/US/partner/docs/ios/iproute/command/reference/irp_bgp1.html#wp1012195


Also, this document may be very interesting to read:


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


Best regards,

Peter

Peter Paluch Mon, 02/15/2010 - 15:06
User Badges:
  • Cisco Employee,

Tom,


Thank you for the link!


Best regards,

Peter

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