Mpls Pdf
To understand MPLS there are two questions we need to answer:. What is MPLS?.
Why do we need MPLS?I’m going to start this lesson with an explanation of why we need it and how MPLS solves some of the issues of other protocols, this will help you to understand why we use MPLS. In the second part of this lesson you will learn what MPLS is and how it actually works.When you want to learn MPLS, you need to be very familiar with the following topics before you continue:. IGPs (like and ). Tunneling.Having said that, let’s get started!
Why do we need MPLS?Take a look at the following picture:Above we have an example of an ISP with two customers called “A” and “B”. The ISP only offers Internet connectivity and no other services. Each customer uses the ISP to have connectivity between their sites.To accomplish our goal, the ISP is running eBGP between the CE (Customer Edge) and PE (Provider Edge) to exchange prefixes. This means all internal (P) routers of the ISP have to run or they don’t know where to forward their packets to.A full internet routing table currently has 500.000 prefixes and with 8 ISP routers running iBGP, we need 28 iBGP peerings. We can reduce this number by using or a. All routers have to do lookups in the routing table for any possible destination.Now here’s something to think aboutwhen our goal is to have connectivity between two customer sites, why should all internal P routers know about this? The only routers that need to know how to reach the customer sites are the PE routers of the provider.
Why not build a tunnel between the PE routers? Take a look at the picture below:In the picture above I added two GRE tunnels:. The two PE routers at the top will use a GRE tunnel for the customer A sites.
The two PE routers at the bottom will use a GRE tunnel for the customer B sites.With a solution like this, we can have a BGP free core! There’s only two places where we need BGP:. eBGP between the PE and CE router. iBGP between two PE routers.Let’s take a closer look at the solution I described above.
Tunnel between PE routersLet’s take a look at the example above in action. I will use the following topology for this:The topology above is a smaller version of the topology I showed you before. This is the ISP with only one customer.
We’ll use a GRE tunnel between PE1 and PE2 so that we don’t need iBGP on the P router. Let me walk you through the entire configuration OSPF ConfigurationFirst we will configure OSPF on all ISP routes so that PE1 and PE2 are able to reach each other. I’ve added some loopback interfaces on the ISP routers that will be advertised as well: PE1(config)# router ospf 1PE1(config-router)# network 192.168.23.0 0.0.0.255 area 0PE1(config-router)# network 2.2.2.2 0.0.0.0 area 0 P(config)# router ospf 1P(config-router)# network 192.168.23.0 0.0.0.255 area 0P(config-router)# network 192.168.34.0 0.0.0.255 area 0P(config-router)# network 3.3.3.3 0.0.0.0 area 0 PE2(config)# router ospf 1PE2(config-router)# network 192.168.34.0 0.0.0.255 area 0PE1(config-router)# network 4.4.4.4 0.0.0.0 area 0That takes care of all internal routing for the ISP.
EBGP ConfigurationLet’s continue by configuring eBGP between the CE and PE routers. We will advertise a loopback on each CE router: CE1(config)# router bgp 10CE1(config-router)# neighbor 192.168.12.2 remote-as 1234CE1(config-router)# network 1.1.1.1 mask 255.255.255.255 PE1(config)# router bgp 1234PE1(config-router)# neighbor 192.168.12.1 remote-as 10 PE2(config)# router bgp 1234PE2(config-router)# neighbor 192.168.45.5 remote-as 20 CE2(config)# router bgp 20CE2(config-router)# neighbor 192.168.45.4 remote-as 1234CE2(config-router)# network 5.5.5.5 mask 255.255.255.255That takes care of eBGP. GRE Tunnel ConfigurationNow we can configure the GRE tunnel between PE1 and PE2. I will use their loopback interfaces as the source and destination. We will use the 192.168.24.0 /24 subnet on the tunnel interfaces: PE1(config)# interface tunnel 0PE1(config-if)# tunnel source 2.2.2.2PE1(config-if)# tunnel destination 4.4.4.4PE1(config-if)# ip address 192.168.24.2 255.255.255.0 PE2(config)# interface tunnel 0PE2(config-if)# tunnel source 4.4.4.4PE2(config-if)# tunnel destination 2.2.2.2PE2(config-if)# ip address 192.168.24.4 255.255.255.0Now we have a working GRE tunnel. IBGP ConfigurationWith the GRE tunnel up and running, we can configure iBGP between the two PE routers: PE1(config)# router bgp 1234PE1(config-router)# neighbor 192.168.24.4 remote-as 1234PE1(config-router)# neighbor 192.168.24.4 next-hop-self PE2(config)# router bgp 1234PE2(config-router)# neighbor 192.168.24.2 remote-as 1234PE2(config-router)# neighbor 192.168.24.2 next-hop-selfOur PE routers will establish an iBGP peering using the IP addresses on the GRE tunnel.
I also could have established iBGP between the loopback interfaces of PE1 and PE2 instead of the IP addresses of the tunnel interfaces. The advantage is that BGP traffic between PE1 and PE2 wouldn’t be encapsulated by GRE. The downside however is that you will need to configure a route-map that changes the next hop IP address of all prefixes learned through BGP to the IP addresses of the tunnel interfaces.Our configuration is now complete.
Let’s find out if it works shall we? VerificationI’ll do a trace from CE1 to CE2: CE1# traceroute 5.5.5.5 source loopback 0Type escape sequence to abort.Tracing the route to 5.5.5.5VRF info: (vrf in name/id, vrf out name/id)1 192.168.12.2 0 msec 0 msec 0 msec2 192.168.24.4 0 msec 0 msec 4 msec3 192.168.45.5 0 msec 0 msec.Great, it’s working! The ISP has a BGP-free core. Here’s what an IP packet from CE1 to CE2 looks like to the P router:The outer IP header has source address 2.2.2.2 and destination address 4.4.4.4, the P router knows how to route these since it learned these addresses through OSPF. Hostname PE1!ip cef!interface Loopback0ip address 2.2.2.2 255.255.255.255!interface Tunnel0ip address 192.168.24.2 255.255.255.0tunnel source 2.2.2.2tunnel destination 4.4.4.4!interface GigabitEthernet0/1ip address 192.168.12.2 255.255.255.0!interface GigabitEthernet0/2ip address 192.168.23.2 255.255.255.0!router ospf 1network 2.2.2.2 0.0.0.0 area 0network 192.168.23.0 0.0.0.255 area 0!router bgp 1234bgp log-neighbor-changesneighbor 192.168.12.1 remote-as 10neighbor 192.168.24.4 remote-as 1234neighbor 192.168.24.4 next-hop-self!end PE2.
Hostname PE2!ip cef!interface Loopback0ip address 4.4.4.4 255.255.255.255!interface Tunnel0ip address 192.168.24.4 255.255.255.0tunnel source 4.4.4.4tunnel destination 2.2.2.2!interface GigabitEthernet0/1ip address 192.168.45.4 255.255.255.0!interface GigabitEthernet0/2ip address 192.168.34.4 255.255.255.0!router ospf 1network 4.4.4.4 0.0.0.0 area 0network 192.168.34.0 0.0.0.255 area 0!router bgp 1234bgp log-neighbor-changesneighbor 192.168.24.2 remote-as 1234neighbor 192.168.24.2 next-hop-selfneighbor 192.168.45.5 remote-as 20!endGreat! Now you might be thinkingso what? Where’s MPLS?For now, keep in mind that tunneling is used to create a BGP free core. Hold this thought while you read the next section of this lesson where we finally start talking about MPLS! What is MPLS?In the previous example I used a GRE tunnel but I could have used any tunneling mechanism. Hostname PE1!ip cef!interface Loopback0ip address 2.2.2.2 255.255.255.255!interface GigabitEthernet0/1ip address 192.168.12.2 255.255.255.0!interface GigabitEthernet0/2ip address 192.168.23.2 255.255.255.0mpls ip!router ospf 1network 2.2.2.2 0.0.0.0 area 0network 192.168.23.0 0.0.0.255 area 0!router bgp 1234bgp log-neighbor-changesneighbor 4.4.4.4 remote-as 1234neighbor 4.4.4.4 update-source Loopback0neighbor 4.4.4.4 next-hop-selfneighbor 192.168.12.1 remote-as 10!end PE2. Hi Praveen,These are different topics with different solutions. First of all, keep in mind that VPN is often used to talk about encryption / authentication / security but this is not always the case.
Even a VLAN could be considered a VPN, it’s “virtual” and a “private network”.Let me give you a quick overview in a nutshell:. MPLS VPN: we use this for connectivity. Service providers offer MPLS for remote connectivity. For details, check the. The 'VPN' part of MPLS is that we use VRFs to separate customer routing information and we create unique. HiIt might help to think about this the other way around, let’s say we don’t use MPLS but BGP on all P and PE routers. This means that:.
The P routers have to do a lookup in their routing tables for every destination. The P routers have to know about every destinationthis means you’ll have to redistribute customer information into BGP.
iBGP has to be a full mesh so if you add another P router in your network, you’ll have to establish neighbor adjacencies with all other iBGP routers. You can make your life a bit easier with an.
Chapter 1 MPLS BasicsThe exponential growth of the Internet over the past several years has placed a tremendous strain on the service provider networks. Not only has there been an increase in the number of users but there has been a multifold increase in connection speeds, backbone traffic and newer applications. Initially ordinary data applications required only store and forward capability in a best effort manner.
However, MPLS brings many other benefits to IP-based networks. Forwarding packets based on labels rather than routing them based on headers results in several important advantages:. Since a packet is assigned to a FEC when it enters the network, information that cannot be gleaned from the network layer header, can be used for FEC assignment. For example, classification of packets based on the source of the packets. Packets can be assigned a priority label, making Frame Relay and ATM-like quality-of-service guarantees possible. This function relates to the CoS field.
Mpls Cisco
The considerations that determine how a packet is assigned to a FEC can become ever more and more complicated, without any impact at all on the routers that merely forward labeled packets. Packet payloads are not examined by the forwarding routers, allowing for different levels of traffic encryption and the transport of multiple protocols. In MPLS, a packet can be forced to follow an explicit route rather than the route chosen by normal dynamic algorithm as the packet travels through the network. This may be done to support traffic engineering, as a matter of policy or to support a given QoS.In addition to all the above advantages, one of the most important advantages of MPLS is that it is independent of the layer 2 and layer 3 technologies and hence allows integration of networks with different layer 2 and layer 3 protocols.