Hello,
When your network is the destination and there are two entry points into your network that are determined via BGP, the first thing you should know is that the final say for any incoming traffic as to which link will be used, is that of the ISP(s). You can attempt to influence routing towards your network that is routed via BGP, but you cannot obligate its behaviour. If the ISPs choose to ignore your “influence” they can.
From an administration point of view, if both links are from the same ISP, then you can talk to them and devise a way to get the traffic more evenly distributed. If they’re not from the same ISP, then it is much more difficult. You will have to resort to trying to influence traffic.
There are several ways to influence inbound traffic, but keep the following key points in mind:
**You do not have ultimate control of how traffic enters your AS. Your ISPs may have outbound policies that will override all of your attempts to influence inbound traffic**
Methods that can be used to influence traffic include:
* Leaking more specific routes
* MED
* AS-PATH Prepending
* Community/Local Pref agreement
To influence the inbound traffic path, customers can use certain attributes (such as MED, AS-PATH, BGP communities) in the updates sent to their providers. Another method is based on the longest prefix-matching behavior and can be accomplished by the BGP conditional route injection.
MED (or metric) is the sixth BGP attribute:
MED can be used to advertise to your neighbors how they should enter your AS.
MED is exchanged between autonomous systems.
The lowest MED is the preferred path.
MED is propagated to all routers within the neighbor AS but not passed along any other autonomous systems.
The fourth BGP attribute is called AS Path:
BGP path attributes also influence inbound/outbound traffic management control over the IP route which give control to administrator to help in selection best network route over the internet.
BGP operates several attributes to determine the best path to a destination.
Border Gateway Protocol (BGP) routers normally receive multiple route to a destination. In BGP routing domain BGP attributes are tend to decide that which of the best path would be to install in the IP routing table ,which would be used to traffic forwarding.
Thanks
