Specifications

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Cisco IGX 8400 Series Provisioning Guide, Release 9.3.3 and Later Releases
OL-1166-04
Chapter 10 Cisco IGX 8400 Series IP Service
IP Service—Functional Overview
Without MPLS, IP transport over ATM networks require a complex hierarchy of translation protocols
to map IP addressing and routing into ATM addressing and routing.
MPLS eliminates complexity by mapping IP addressing and routing information directly into ATM
switching tables. The MPLS label-swapping paradigm is the same mechanism that ATM switches use to
forward ATM cells. This solution has the added benefit of allowing service providers to continue
offering their current Frame Relay, leased-line, and ATM services portfolio while enabling them to
provide differentiated business-quality IP services.
Built-In VPN Visibility
To cost-effectively provision feature-rich IP VPNs, providers need features that distinguish between
different types of application traffic and apply privacy and QoS—with far less complexity than an
overlay IP tunnel, Frame Relay, or ATM “mesh.”
Compared to an overlay solution, an MPLS-enabled network can separate traffic and provide privacy
without tunneling or encryption. MPLS-enabled networks provide privacy on a network-by-network
basis, much as Frame Relay or ATM provides it on a connection-by-connection basis. The Frame Relay
or ATM VPN offers basic transport, whereas an MPLS-enabled network supports scalable VPN services
and IP-based value added applications. This approach is part of the shift in service provider business
from a transport-oriented model to a service-focused one.
In MPLS-enabled VPNs, whether over an IP switched core or an ATM LSR switch core, the provider
assigns each VPN a unique identifier called a route distinguisher (RD) that is different for each intranet
or extranet within the provider network. Forwarding tables contain unique addresses, called VPN-IP
addresses (see Figure 10-12), constructed by linking the RD with the customer IP address. VPN-IP
addresses are unique for each endpoint in the network, and entries are stored in forwarding tables for
each node in the VPN.
Figure 10-12 VPN-IP Address Format
BGP Protocol
Border Gateway Protocol (BGP) is a routing information distribution protocol that defines who can talk
to whom using MPLS extensions and community attributes. In an MPLS-enabled VPN, BGP distributes
information about VPNs only to members of the same VPN, providing native security through traffic
separation. Figure 10-13 shows an example of a service provider network with service provider edge
label switch routers (PE) and customer edge routers (CE). The ATM backbone switches are indicated by
a double-ended arrow labeled “BGP.”
RD IP Address/mask length
0.1.0.99 130.101.0.0/16
General format
VPN-IPv4 example
RD is a 64-bit route distinguisher
• Never carried on packets, only in label tables
Each customer network can use:
• Registered IP addresses
• Unregistered addresses
Private addresses (RFC 1918, for example, 10.x.x.x)
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