MPLS on EIGRP:
The MPLS VPN Support for EIGRP between Provider Edge (PE)
and Customer Edge (CE) feature introduces the capability to
redistribute Enhanced Interior Gateway Routing Protocol (EIGRP)
routes through a Multiprotocol Label Switching (MPLS) Virtual
Private Network (VPN) over a Border Gateway Protocol (BGP) core
network. This feature is configured only on PE routers and requires
no upgrade or configuration changes to customer equipment. This
feature also introduces EIGRP support for MPLS and support for
EIGRP extended community attributes. Customer networks and remote
sites are connected to each other through the MPLS VPN. The
configuration of this feature allows several EIGRP sites to
connect seamlessly and appear as a single network. This integration
is transparent to the customer sites. When this feature is enabled,
EIGRP routes are converted to iBGP routes and transported through
the BGP core network. EIGRP extended community attributes are
used to define EIGRP routes and preserve internal metrics. These
attributes are carried across the core network by multiprotocol
BGP. A single EIGRP routing process can support multiple VRFs.
This support is limited only by the available system resources
on the router, which are determined by the number of configured
VRF instances, running processes, and amount of available memory.
However, only a single VRF can be supported by each VPN.
MPLS on BGP:
An Multiprotocol Label Switching (MPLS)-based virtual private
network (VPN) has three major components:
- VPN route target communities-A VPN route target community
is a list of all members of a VPN community. VPN route targets
need to be configured for each VPN community member.
- Multiprotocol BGP (MP-BGP) peering of VPN community
provider edge (PE) devices-MP-BGP propagates virtual routing
and forwarding (VRF) reachability information to all members
of a VPN community. MP-BGP peering must be configured on
all PE devices within a VPN community.
- MPLS forwarding-MPLS transports all traffic between
all VPN community members across a VPN service-provider
network. A one-to-one relationship does not necessarily
exist between customer sites and VPNs. A given site can
be a member of multiple VPNs. However, a site can associate
with only one VRF. A customer-site VRF contains all the
routes available to the site from the VPNs of which it is
a member.
Router>enable
Router#configure terminal
Router(config)#router bgp as-number
Router(config-router)# no bgp default ipv4-unicast
Router(config-router)#neighbor {ip-address | peer-group-name} remote-as as-number
Router(config-router)#neighbor {ip-address | peer-group-name} activate
Router(config-router)#address-family vpnv4 [unicast]
Router(config-router)#neighbor {ip-address | peer-group-name} send-community extended
Router(config-router)#neighbor {ip-address | peer-group-name} activate
Router(config-router)#end
A predefined path that makes MPLS work are called Label Switched
Paths. In a MPLS network router exchange MPLS information to
exchange these paths. MPLS is often called a layer 2.5 technology
because it shares both routing (layer 3) and switching (layer
2) characteristics.
a.LDP: MPLS LDP enables the peer
LSR in an MPLS network to exchange label binding information
for supporting hop-by-hop forwarding in an MPLS network. MPLS
LDP provides the means for LSRs to request, distribute, and
release label prefix binding information to peer routers in
a network. LDP enables LSRs to discover potential peers and
to establish LDP sessions with those peers for the purpose of
exchanging label binding information.
MPLS LDP enables one LSR to inform another LSR of the label
bindings it has made. Once a pair of routers communicates the
LDP parameters, they establish a label-switched path (LSP).
MPLS LDP enables LSRs to distribute labels along normally routed
paths to support MPLS forwarding. This method of label distribution
is also called hop-by-hop forwarding. With IP forwarding, when
a packet arrives at a router the router looks at the destination
address in the IP header, performs a route lookup, and forwards
the packet to the next hop. With MPLS forwarding, when a packet
arrives at a router the router looks at the incoming label,
looks up the label in a table, and then forwards the packet
to the next hop. MPLS LDP is useful for applications that require
hop-by-hop forwarding, such as MPLS VPNs.
b. MPLS VPN: "MPLS" and "VPN" are
two different technology types MPLS is a standards-based technology
used to speed up the delivery of network packets over multiple
protocols -such as the Internet Protocol, Asynchronous Transport
Mode, and Frame-Relay network protocol. A virtual private network
(VPN) uses shared public telecom infrastructure, such as the
Internet, to provide secure access to remote offices and users
in a cheaper way than an owned or leased line. VPNs are secure
because they use tunneling protocols and procedures such as
Layer Two Tunneling Protocol (L2TP). With those definitions
understood, an MPLS VPN is a VPN that is built on top of an
MPLS network, usually from a service provider, to deliver connectivity
between enterprise office locations.
There are three kinds of MPLS-based VPN:
- Layer 3 VPNs: With L3 VPNs the service
provider participates in the customer's Layer 3 routing.
The customer's CE router at each site speaks a routing protocol
such as BGP or OSPF to the provider's PE router, and the
IP prefixes advertised at each customer site are carried
across the provider network. L3 VPNs are attractive to customers
who want to leverage the service provider's technical expertise
to insure efficient site-to-site routing.
- Layer 2 VPNs: The provider interconnects
the customer sites via the Layer 2 technology - usually
ATM, Frame Relay, or Ethernet - of the customer's choosing.
The customer implements whatever Layer 3 protocol he wants
to run, with no participation by the service provider at
that level. L2 VPNs are attractive to customers who want
complete control of their own routing; they are attractive
to service providers because they can serve up whatever
connectivity the customer wants simply by adding the appropriate
interface in the PE router.
- Virtual Private LAN Service: VPLS makes
the service provider's network look like a single Ethernet
switch from the customer's viewpoint. The attraction of
VPLS to customers is that they can make their WAN look just
like their local campus- or building-scope networks, using
a single technology (Ethernet) that is cheap and well understood.
Unlike traditional Metro Ethernet services built around
actual Ethernet switches, service providers can connect
VPLS customers from regional all the way up to global scales.
So a customer with sites in London, Dubai, Bangalore, Hong
Kong, Los Angeles, and New York can connect all his sites
with what appears to be a single Ethernet switch.
c. MPLS on RIP:RIPv2 is one of
the protocols that can be used between customer's edge router
and provider's edge router. CE to PE support RIP as one of the
dynamic routing protocols. Version 2 is supported. There are
few features in MP-BGP that preserve protocol specific information
that would be lost in redistribution, mainly the RIP metric.
One feature is to preserve the RIP metric across the MPLS network
by putting it in the MED attribute and during redistribution
use that as the RIP metric. This helps in topologies when there
are backdoor links (directly connected RIP and MPLS connected).MPLS
VPN hop won't be considered as a RIP hop, so a metric of 0 will
be maintained. While a backbone connection will add one hop.
Metric transparent- Causes RIP to use the routing table metric
for redistributed routes as the RIP metric. IOS-XR will automatically
redistribute metric transparently without any commends. This
could be confusing at first, trying to find a command that doesn't
exist. IOS-XR can have an issue if the directly connected interface
is redistributed to BGP-MP. It will redistribute it with metric
0 and not accept it.
R1 (config)#router rip
R1(config-router)# address-family ipv4 vrf (Vrf)
R1(confif-router)# redistribute bgp 100 metric transparent
