Thursday, August 11, 2011

Configuring MPLS L3VPNs

Imagine Site A-1 is in Georgia, A-2 is in Illinois and A-3 is in New York. Full connectivity between all Site A-#s is required. What are our options? Well you can do a full mesh VPN and using the formula n(n-1)/2 where n is the # of sites you can see that we would need to build 6 static VPN tunnels -- needless to say static tunnels are time consuming and does not scale well. Or you can set up DMVPN (Cisco proprietary) which would lessen the work. Or as an ISP we can provide MPLS VPN and the customers wont have to do ANYTHING which is just way they usually like it. Customer site Site A-#s and Customer Site B-#s can all be VPN'd together appropriately and transparently using MPLS.

Consider the topology below.

Configure R1 and R2 to support MPLS/OSPF/BGP
Configure the appropriate VRFs on R1 and R2
All Site A routers (R3, R4 and R7) should all be able to transparently ping all Site-A#s loopbacks
All Site B routers (R5 and R6) should all be able to transparently ping all Site-B#s loopbacks
Site A routers (R3, R4, R7) should not be able to ping Site B routers (R5 and R6) and vice-versa

Relevant configurations are posted below. So let's jump right into the complex world of MPLS!!

Configuring BGP - Dual Multihomed Design

We've already laid out the ground work in my previous blogtorial "Configuring BGP - Dual Homed Design". So all we are going to have to do is bring up 2 more bgp peers. 1 on R1 and 1 on R2 to connect ISP-B with the ASN 33333.

Here is the topology so let's get going.

Relevant configurations are posted below.

Wednesday, August 10, 2011

Configuring BGP - Dual Homed Design (Part 2)

In "Configuring BGP - Dual Homed Design (Part 1)" we saw how we can configure R1 and R2, however R3 in the enterprise core still cannot get access to the internet. So let's configure dual NAT on R1 and R2 and learn 'why and how' we redistribute iBGP learned routes into OSPF. 

Configuring BGP - Dual Homed Design (Part 1)

In this blogtorial we will discuss how to implement a Dual Homed BGP design. So let's begin by defining what is a Dual Homed BGP design? Dual Homed BGP means you have 2 local routers (in the same ASN) connected to the 2 different routers from the same ISP. A Dual Homed setup will give you fault tolerant at the router level but not at the ISP level. Consider a Single Multihomed or Dual Multihomed setup for fault tolerant at the ISP level. These are fairly advanced topics so I suggest you familiarize yourself with BGP, BGP path selection, route-maps, prefix-lists, OSPF, route-distribution before continuing. 

  • Configure OSPF as IGP for R1, R2, R3
  • Configure iBGP between R1 and R2
  • Configure iBGP between R4 and R5
  • Configure eBGP between R1 and R4 
  • Configure eBGP between R2 and R5
See below for the network diagram to better understand a Dual Homed BGP Design.

Relevant configurations are posted below so let's get started.

Tuesday, August 9, 2011

Configuring BGP - Single Multihomed Design

This blogtorial is a continuation from my previous "Configuring BGP - Single Homed". The topology now has a new ISP (ISP B) connected to R1. So R1 now has 2 internet connections. Keep in mind that load balancing is not possible in a Single Multihomed configuration because BGP will install only the best route. However load sharing and failover is possible. Load-sharing in this context means you take in a full BGP routing table and set metrics appropriately.

  • and will be advertised by both ISP A and ISP B
  • Configure R1 to load share between the 2 ISPs
    • R1 will prefer ISP A for
    • R1 will prefer ISP B for 
  • Advertise to both the ISPs so when one of the ISP goes down incoming traffic to is not affected. 

Relevant configurations are posted below so let's get started.

Sunday, August 7, 2011

Configuring BGP - Single Homed Design

BGP is a highly complex routing protocol -- so complex that there are exams dedicated to just this protocol. Therefore, I will not dwell on the details and the inner workings of BGP, however I will give you a brief how-to implement a "Single Homed" BGP design

When it comes to BGP designs they are four basic ones: single homed, dual homed, single multihomed and dual mutihomed. In this blogtorial we are going to see how to implement a "Single homed" BGP design

Here is the topology which I will be using and we will be building upon this topology on future BGP blogtorials so let's get started. 
Relevant configurations are posted below.