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Tag Archives: BGP

routing policy configuration

Some time ago I wrote about local PBR and interface PBR.

It’s time to talk about routing policy, that is a different mechanism. Routing policy is applied to routing information and it is combined with routing protocols to form policies. PBR mechanism is applied to data flows and and packets are forwarded according to the configured policy.

Routing policy is a tool which can be used to filter routes and set route attributes, when importing routing information into OSPF, RIP, ISIS or BGP protocols. BGP can use routing policy to filter advertising routes as well. Routing policy defines which of the routes from the specific routing protocol are allowed to be imported into the target routing protocol. It can be also used to match routes or certain route attributes and to change these attributes when the matching rules are met.

Routing policy command syntax:
route-policy route-policy-name { permit | deny } node node

A route-policy may consists of multiple nodes, for example:

route-policy LABNARIO-POLICY permit node 10
route-policy LABNARIO-POLICY deny node 20

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BGP MED attribute on Huawei router

Some time ago I published article about BGP local preference attribute. Today I’d like to show you how to configure BGP MED attribute.

What is it for?

The multi-exit discriminator MED determines an optimal route for incoming traffic of an AS. When a BGP device obtains multiple routes to the same destination but with different next hops from EBGP peers, the BGP device selects the route with the smallest MED value as the optimal route. Simply saying, configuring MED attribute, we would like to show the next hop for traffic coming from EBGP peer. The MED attribute is exchanged only between two neighboring ASs. The AS that receives the MED attribute does not advertise it to any other ASs.

Let’s look at typical scenario for MED attribute configuration:

BGP MED topology

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hub&spoke in BGP/MPLS VPN

Some time ago we talked about a basic configuration of BGP/MPLS VPNs. Let’s go on with hub&spoke networking today. Such solution can be adopted to control the mutual access of users, when an access control device is set. In this case no direct route exists between spoke sites. A spoke site advertises routes to a hub site and then the hub site advertises the routes to other spoke sites. Thus, communication between spoke sites is controlled by hub site.

Let’s look at our topology:

MPLS L3VPN hub and spoke topology

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MPLS L3VPN on Huawei routers

  1. CE1 and CE5 are in VPN labnario_1
  2. CE2 and CE8 are in VPN labnario_2
  3. ISIS level -2 as IGP
  4. Connections CE1—PE3 and CE5—PE4 – static routes
  5. Connection CE2—PE3 – OSPF
  6. Connection CE8—PE4 – EBGP
  7. Users in different VPNs cannot access each other.

A BGP/MPLS IP VPN uses the Border Gateway Protocol (BGP) to advertise VPN routes and the Multiprotocol Label Switching (MPLS) to forward VPN packets on backbone networks.

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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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