BGP incoming traffic

Routing & Switching BGP
1

Hello Rene & Team,

Good Day to you,

Can you please give me any example how BGP handle incoming traffic ? lets say I advertise 1.1.1.0/24 network to two different ISP. in this case how bgp will handle incoming traffic to 1.1.1./24.

Thank you
Mehul.

2

Hi Mehul,

Do you mean how BGP decides which path to take? BGP has a big list with attributes that it checks in order to decide what the “best path” is. Look for the How the Best Path Algorithm Works section of this document if you want to see the detailed version:

3

Hi Rene,

Thanks for your input.
yes I meant to that but for INCOMING traffic. How to handle incoming traffic. can i load balance incoming traffic.

4

Hi Mehul,

In BGP, you can use AS path prepending and/or MED to influence this yes. Here are some examples:

https://networklessons.com/bgp/how-to-configure-bgp-med-attribute/

https://networklessons.com/bgp/how-to-configure-bgp-as-path-prepending/

5

Thanks rene,. really appreciate

6

Hello Rene,
Suppose a router has to connections with 10G bandwidth, but the 2 lines have imbalance traffic of 7G and 4G BW. How would correct the situation or what would you do in this case?

7

Hello sed

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.

I hope this has been helpful!

Laz