BGP

6PE – IPv6 over MPLS

6PE is a really cool feature which allows IPv6 islands to communicate with each other over an MPLS/IPv4 core network.  IPv4 addresses space is fast running out so familiarising yourself with IPv6 is probably a good idea.
Consider the toplogy below.

Service providers can leverage their MPLS networks to deliver IPv6 solutions without having to rearchitect their [...]

BGP – Remove Private AS

The video below shows how to remove a private AS from BGP as-path list.
Consider the topology below.
AS65300 peers eBGP with R1.  R1 then peers eBGP with R2.
R1 is then configured to remove all private ASs in the as-path when it advertises BGP routes to R2.
Watch the video below or download and watch it on your [...]

eBGP multihop

eBGP multihop can be used to loadshare traffic across multiple links between eBGP peers.
Consider the topology below.

By default eBGP sessions can only be established between directly connected interfaces.  If you want to connect to a non-connected interface or to a non-connected neighbor, you have to use the eBGP-multihop feature.
For this to work, you need to [...]

BGP – Prefix aggregation using a static route

My previous post on BGP prefix aggregation used the bgp “aggregate-address” command.  Another way to generate an aggregate is by using a static route.
Consider the toplology below.
Watch the video below to see how to configure a BGP aggregate using a static route.  Alternatively down the video here and watch it on your iPod.
The commands used [...]

BGP peer-groups and dynamic update peer groups

One of many optimizations for BGP is the peer-groups feature.
BGP peer-groups allow you to group BGP peers which have the same outbound policy.  There are 2 obvious benefits for doing this.

Reduced the amount of configuration required.
BGP can send a single update to many peers.

Both of these need some clarification.
Consider the topology below.

Lets look at the [...]

Prefix Lists

IP Prefix lists can be used with BGP to permit or deny specific prefixes from being advertised or learnt to or from a neighbor.
Consider the topology below.

We will carry out three exercises.

configure a prefix list to match 192.168.1.0/24
configure a prefix list to match 192.168.1.0/24, 192.168.1.0/25, 192.168.1.0/26.
configure a prefix list to match 192.168.1.0/25 and 192.168.1.0/26

Exercise 1
We [...]

ARF – Automatic Route Filtering

When designing an MPLS network you will have to decide whether to configure a full mesh of MP-iBGP sessions between your PEs as in diagram 1 below or whether to use a hub and spoke topology as in diagram 2 below.
Diagram 1 – BGP full mesh

Diagram 2 – BGP partial mesh

The most obvious benefit of [...]

AFIs and SAFIs

BGP uses Open messages to negotiate BGP sessions.  These Open messages have optional parameters which allow additional capabilities to be negotiated during setup.
If you want to run anything other than IPv4 unicast then you will have to configure BGP to advertise its additional capabilities i.e. Multi-Protocol extensions (AFI/SAFI) during initial setup.
As an example you may [...]

BGP Route Aggregation

There are times when it is required to aggregate a set of prefixes.  There are a number of reasons why you would want to do this such as, your peering transit edge may not accept certain size prefixes, you may want to reduce the size of the routing table in some part of your network [...]

IPv4 BGP multicast

IPv4 BGP multicast announcements can be somewhat confusing.  It took a while to get my head around it, so now that I have, I will try to explain.
I have set up the topology below.

Everything has been configured in the above scenario EXCEPT the IPv4 BGP multicast session between RP and ASBR-RP.  I want to show [...]