Monday , October 15 2018
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Tag Archives: BGP attributes

BGP LocPref once again

Let’s keep going and try to configure BGP local preference attribute using route-policy.

We can take full advantage of topology and configuration from the last post: “BGP default local preference in Huawei CLI“.

  1. Assure full connectivity based on the attached topology (look at the previous article).
  2. Configure Loopback 10 and Loopback 20 on router AR4.
  3. Import all Loopback interfaces of router AR4 to BGP.

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BGP default local preference in Huawei CLI

Let’s assume that we have a topology like in below picture:

  1. AR1, AR2 and AR3 are in AS 100.
  2. AR4 is in AS 200.
  3. Loopback 100 of router AR1 and loopback 0 of router AR4 are advertised by BGP.

What we want to do is to configure default local preference attribute, which will determine the optimal route, for traffic that leaves AS 100. In our case, the whole traffic leaving AS 100 will go through AR3.

If a BGP device obtains multiple routes from different IBGP peers and these routes have different next hops to the same destination, the BGP device will select the route with the greatest Local_Pref value.

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basic BGP in Huawei CLI

BGP stands for Border Gateway Protocol. It is widely used among Internet Service Providers to make core routing decisions on the Internet. The current BGP version is BGP-4 defined in RFC 4271.

BGP uses TCP port 179 as its underlying delivery mechanism to increase the reliability of the peer connection. BGP is called a path vector routing protocol. It uses a list of AS numbers through which the packet must pass in order to reach the destination. This list of AS numbers is associated with a BGP route and is called the AS_Path attribute. AS_Path is one of several path attributes associated with each BGP route. How does a BGP select best path to a destination network, you can read at how does BGP select routes.

I do not want to describe BGP in details, as this is out of the scope of this article. What I want to do is to show you, how to configure basic BGP features using Huawei CLI. Especially I want to show you how to:

  • run BGP protocol
  • configure IBGP peering sessions using peer groups
  • configure EBGP peering
  • advertise networks.

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