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Cisco uBR7200 Series Universal Broadband Router Software Configuration Guide
OL-2239-05
Chapter1 Overview of Cisco uBR7200 Series Software
cops tcp window-size
Using MPLS VPN technology, service providers can create scalable and efficient private networks using
a shared hybrid fiber-coaxial (HFC) network and IP infrastructure. The cable MPLS VPN network
consists of this infrastructure:
• The multiple service operator (MSO) or cable company that owns the physical infrastructure and
builds VPNs for the Internet service providers (ISPs) to move traffic over the cable and IP backbone.
• ISPs that use the HFC network and IP infrastructure to supply Internet service to cable customers.
Each ISP moves traffic to and from a subscriber's PC, through the MSO's physical network
infrastructure, to the ISP's network. MPLS VPNs, created in Layer 3, provide privacy and security by
constraining the distribution of a VPN’s routes to only the routers that belong to its network. Thus, each
ISP's VPN is insulated from other ISPs that use the same MSO infrastructure.
An MPLS VPN assigns a unique VPN Routing/Forwarding (VRF) instance to each VPN. A VRF instance
consists of an IP routing table, a derived forwarding table, a set of interfaces that use the forwarding table,
and a set of rules and routing protocols that determine the contents of the forwarding table. Each PE router
maintains one or more VRF tables. It looks up a packet’s IP destination address in the appropriate VRF table,
only if the packet arrived directly through an interface associated with that table. MPLS VPNs use a
combination of Border Gateway Protocol (BGP) and IP address resolution to ensure security.
Refer to the chapter “Configuring Multiprotocol Label Switching” in the Cisco IOS Switching Services
Configuration Guide, Release 12.2 on Cisco.com.
Overlapping Subinterface IP Addresses
Multiprotocol Label Switching (MPLS)-based Virtual Private Networks (VPNs) are created in Layer 3,
and provide privacy and security by constraining the distribution of a VPN's routes to those routers that
are members of the VPN only, and by using MPLS forwarding. Each ISP's VPN is insulated from all
others sharing the HFC and IP-over-cable infrastructure. MPLS VPN enforces traffic separation by
assigning a unique VPN Routing/Forwarding (VRF) instance to each VPN. A VRF instance consists of
an IP routing table, a derived forwarding table, a set of interfaces that use the forwarding table, and a set
of rules and routing protocols that determine what is in the forwarding table.
Cisco IOS Release 12.1(2)EC1 and earlier releases assumed that IP addresses were unique, but it is
possible with an MPLS VPN to configure overlapped IP addresses within a VRF. A configuration of
overlapped IP addresses could have caused errors. Cisco IOS Release 12.1(3)EC supports a
configuration of overlapping IP addresses for subinterfaces. The same IP subnet can now be configured
for CPEs on different VRFs using a Cisco uBR7200 series router to configure an MPLS VPN.
The following CLI commands have been updated in recent Cisco IOS releases to support overlapping IP
addresses on subinterfaces:
New CLI Commands
• cable device {ip-address | mac-address} [no] access-group {access-list | access-name} |
{[vrf vrf-name] ip-address [no] access-group [access-list | access-name]}
• cable host {ip-address | mac-address} [no] access-group {access-list | access-name} |
{[vrf vrf-name] ip-address [no] access-group [access-list | access-name]}
• clear cable host {ip-address | mac-address}
• show cable device [vrf vrfname] [ip-address] access-group
• show cable host [vrf vrfname] [ip-address | mac-address] access-group
Note For the latest command information and detailed command history, refer to the Cisco Broadband Cable
Command Reference Guide on Cisco.com.