Neighborship over WANs ccie course training in gurgaon

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EIGRP configuration and neighborship rules do not differ when comparing typical LAN
and typicalWAN technologies. However, some design and operational differences exist,
particularly regarding which routers become neighbors with which other routers. This short
section closes the EIGRP neighbor discussion with a brief look at Frame Relay, MPLS
VPNs, andMetro Ethernet as implemented with Virtual Private LAN Service (VPLS).
Key
Topic
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Chapter 2: EIGRP Overview and Neighbor Relationships 49
Neighborship on Frame Relay
Frame Relay provides a Layer 2 WAN service. Each router connects to the service using a
physical serial link, called a Frame Relay access link. The provider then creates logical connection,
called permanent virtual circuits (PVCs), which is a logical path between a pair
of routers connected to the Frame Relay service. Any pair of routers that connect to the
ends of a Frame Relay PVC can send Frame Relay frames to each other, IP packets, and
they can become EIGRP neighbors. Figure 2-8 shows a typical case, with R1 as a centralsite
router, and R2, R3, and R4 acting as branch routers.
Figure 2-8 shows EIGRP neighborships, but note that all routers can learn all routes in the
internetwork, even though not all routers become neighbors. The neighborships can only
form when a PVC exists between the two routers.
Frame
Relay
50 CCNP ROUTE 642-902 Official Certification Guide
MPLS
VPNs
R4
Chapter 2: EIGRP Overview and Neighbor Relationships 51
Neighborship on Metro Ethernet
The term Metropolitan Ethernet (MetroE) represents a range of Layer 2 WAN services in
which the CE device connects to the WAN service using some form of Ethernet. Because
MetroE provides a Layer 2 Ethernet service, the service delivers an Ethernet frame sent by
one customer router to one other customer router (for unitcast frames), or to many other
routers (for multicast or broadcast frames).
MetroE encompasses several underlying technologies to create the service. Of note for
the purposes of this book are the Virtual Private Wire Service (VPWS) and the Virtual
Private LAN Service (VPLS). Both technical specifications allow for connections using
Ethernet links, with the service forwarding Ethernet frames. VPWS focuses on point-topoint
topologies, whereas VPLS supports multipoint, approximating the concept of the
entire WAN service acting like one large Ethernet switch. Because it is a Layer 2 service,
MetroE does not have any Layer 3 awareness, and the customer routers (typically referenced
as with the more general service provider term customer premise equipment, or
CPE) see the MetroE service as a VLAN. Because the customer routers connect to the
service as a VLAN, all the routers connected to the service can become EIGRP neighbors,
as shown in Figure 2-10.