AS-Path BGP Attribute

jskfan
jskfan used Ask the Experts™
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If I am not wrong the most used BGP Attributes are
Local Preference, Weight,AS Path, MED

Local Preference and  Weight are used to manipulate the Outgoing Traffic
MED is used to manipulate the Incoming Traffic

This one is confusing:
AS Path: is it used to manipulate both Incoming/Outgoing Traffic ?
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Harold BowlinOwner/Network Architect

Commented:
AS-Path is used for loop prevention. It can also be used if you want to manipulate how traffic is sent back to you/inbound. You can prepend your AS on one of your points of presence, thus making the AS-Path longer to that router. This will cause the peer AS to use the shorter AS-Path to your network.

Author

Commented:
So it is used to manipulate both incoming and outgoing traffic ?
Harold BowlinOwner/Network Architect

Commented:
Well there is a lot to it. In general there are more effective ways to manipulate traffic than using AS-path prepending. You mentioned several above. The key takeaway is the foremost function is loop prevention.
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Author

Commented:
Per this link https://supportforums.cisco.com/discussion/9532491/bgp-inbound-and-outbound-traffic
"When you are multi homed to two different providers it is sometimes required to prefer one provider's link for some incoming traffic"
it sounds like it is used to manipulate traffic entering your AS



but I guess it can also be used to manipulate the traffic leaving your AS
Owner/Network Architect
Commented:
Sorry if my first comment caused some confusion. No, only for inbound. You send something out to manipulate inbound, you make a change on your side to manipulate outbound. It's a little backwards but it's how it works.

Author

Commented:
Thank you

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