BGP Path Attributes – MED

bgp-med

BGP Path Attributes – MED

BGP MED (Multi Exit Discriminator) Attribute is the BGP Path attribute which provides information to the external neighbours, about how to come their Autonomous System. This is opposite of Local Preference. BGP Local Preference Atribute says to the internal neighbours, “How to Exit AS”. BGP MED Attribute says to the external neighbours, “How to Enter AS”.

MED (Multi Exit Discriminator) attribute is applied to the outbound interface and shows the best inbound interface into its AS (Autonomous System).


If BGP Best Path is selected via MED (metric) attribute, the Lowest MED (metric) value is better and it is selected as BGP path. The default MED value is 0.

Local Preference Attribute was sending only to IGP neighbours. BGP MED Attribute can be sent only EGP neighbours. In other words, Local Preference can exchanged in the AS, MED attribute can exchange between ASs.

Here, one of the important point is this, MED attribute can be carried into an AS and used inside this AS. But it does not leave that AS. If leaved, it is set as metric 0.


You can also test yourself with BGP Tests and Questions.


MED (Multi Exit Discriminator) attribute is an Optional and Non-transitive BGP Path attribute. This means that it can be or can not be supported in any BGP implementation and in BGP Update the unsupported attribute is discarded.

MED (Multi Exit Discriminator) attribute is indicated as metric in the BGP table. When you use “show ip bgp” command, you can see the metric value after the neighbour value.

bgp path attribute, MED

BGP Path Attribute, MED


As an important note, there are two commands used with MED attribute. These commands are:

• bgp deterministic-med
• bgp always-compare med

bgp deterministic-med” command provides to compare different MED values that advertised by neighbours in the same AS for routes selection.

bgp always-compare med” command provides to compare different MED values that advertised by neighbours in different ASs for routes selection.


Let’s do an example configuration and understand MED (metric) attribute better.

bgp path attribute, MED

BGP Path Attribute, MED


We're Sorry!

Full Access is for only IPCisco Crew...

With IPCisco Membership, You Can Access:

• All Certification Courses (Cisco, Juniper, Nokia and Huawei),
• Thousands of Questions (Lesson Quizes and Special Quiz Section),
• Carieer Consultancy, CV/Resume Check, Career Advice Meeting,
• Cheat Sheets, Job Interview Trainings, Network Tools,
You will be Member of a Big IPCisco Community,
You will Learn Network Lessons with Always,
New And Different Learning Styles!
We are waiting for you!

Lesson tags: BGP, routing, path attributes
Back to: CCNP Route > BGP

Comments are closed.




CCNP Route