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What is the default intersite IP topology in an MPLS-VPN implementation?

  • Hub and Spoke
  • Partial Mesh
  • Full Mesh (correct)
  • Point-to-Point

    • What is the purpose of the inner label in an MPLS-VPN forwarding mechanism?

  • To identify the VPN (correct)
  • To identify the CE device
  • To identify the destination PE device
  • To identify the service provider network

    • What routing protocol is mandated by RFC 2547 for exchanging prefixes and labels between PE devices in an MPLS-VPN network?

  • EIGRP
  • BGP (correct)
  • OSPF
  • RIP

    • How do CE devices advertise routes to PE devices in an MPLS-VPN network?

    <p>Using either static or dynamic routing</p> Signup and view all the answers

    What is the benefit of MPLS-VPN over dedicated WAN connections between sites?

    <p>Cost-effectiveness</p> Signup and view all the answers

    What is the purpose of the outer label in an MPLS-VPN forwarding mechanism?

    <p>To identify the destination PE device</p> Signup and view all the answers

    How do service providers carry packets to customer routes in an MPLS-VPN network?

    <p>By carrying packets to those routes across its network</p> Signup and view all the answers

    What protocol is CE red1 using to advertise the 192.168.4.0/24 prefix to PE A?

    <p>eBGP</p> Signup and view all the answers

    What routing protocol does CE green2 use?

    <p>RIPv2</p> Signup and view all the answers

    What is the purpose of PE A in the MPLS-based Layer 3 VPN configuration?

    <p>To import prefixes announced by the CE into the route table</p> Signup and view all the answers

    What is the function of iBGP in the MPLS-based Layer 3 VPN configuration?

    <p>To announce reachability for each of its attached customer sites</p> Signup and view all the answers

    What is the next hop for the 192.168.4.0 route on CE red2?

    <p>192.168.2.1</p> Signup and view all the answers

    How does PE A identify the next hop for a packet going from CE green1 to CE green2?

    <p>As a BGP neighbor</p> Signup and view all the answers

    What is the purpose of the label imposed by PE A on the packet going from CE green1 to CE green2?

    <p>To identify the VPN routing table</p> Signup and view all the answers

    How does PE A find the route to 192.168.3.0?

    <p>Through a BGP route</p> Signup and view all the answers

    What is the topology of the iBGP sessions between the PEs?

    <p>Full mesh</p> Signup and view all the answers

    What type of VPN is configured in the given example?

    <p>MPLS based Layer 3 VPN</p> Signup and view all the answers

    What is the purpose of the 'tag-switching ip' command in the interface configuration?

    <p>To enable label switching</p> Signup and view all the answers

    What is a mandatory attribute of every VPN on a Cisco router?

    <p>Dedicated interfaces</p> Signup and view all the answers

    What is used to establish route reachability within an MPLS VPN?

    <p>Selective import of BGP routes</p> Signup and view all the answers

    How many iBGP sessions are established in the given example?

    <p>2</p> Signup and view all the answers

    What is the purpose of a route-target in BGP?

    <p>To associate a numeric value to all exported routes</p> Signup and view all the answers

    What is the purpose of the 'route-target both 101:1' command in the VRF configuration?

    <p>To configure the route-target and RD values</p> Signup and view all the answers

    What is the IP address of the Loopback0 interface?

    <p>12.0.0.1 255.255.255.255</p> Signup and view all the answers

    What is the function of a route-distinguisher in BGP?

    <p>To make private routes globally unique</p> Signup and view all the answers

    What is carried in BGP updates in an MPLS VPN?

    <p>Route-target</p> Signup and view all the answers

    What is the VRF name configured in the given example?

    <p>RED</p> Signup and view all the answers

    What is the purpose of the 'ip vrf forwarding RED' command?

    <p>To forward traffic to the VRF instance</p> Signup and view all the answers

    What is the purpose of the import value in a route-target?

    <p>To filter incoming routes</p> Signup and view all the answers

    What is the purpose of the 'rd 101:1' command in the VRF configuration?

    <p>To configure the RD value</p> Signup and view all the answers

    Why is a route-distinguisher used in an MPLS VPN?

    <p>To avoid conflict in address space</p> Signup and view all the answers

    What is a characteristic of route-targets in an MPLS VPN?

    <p>The import and export values do not have to match</p> Signup and view all the answers

    What is the main application of MPLS that has caused the most interest?

    <p>Layer 3 VPN</p> Signup and view all the answers

    What type of routers exchange routes with service provider edge routers?

    <p>Customer edge routers</p> Signup and view all the answers

    What prevents a CE-PE link from being shared with other customer traffic?

    <p>Standard IP traffic</p> Signup and view all the answers

    What connects customer sites in an MPLS-VPN reference architecture?

    <p>LSRs</p> Signup and view all the answers

    What is a key characteristic of an MPLS-VPN service?

    <p>Sites in a VPN can communicate only with other sites in the same VPN</p> Signup and view all the answers

    What is the function of a PE router in an MPLS-VPN reference architecture?

    <p>To peer with CEs that belong to different customers</p> Signup and view all the answers

    What is the purpose of a VRF in an MPLS-VPN configuration?

    <p>To provide route isolation</p> Signup and view all the answers

    What is the benefit of an MPLS-VPN service over dedicated WAN connections?

    <p>Increased scalability</p> Signup and view all the answers

    What is the purpose of the 'ip vrf forwarding RED' command?

    <p>To specify the VRF for the VPN</p> Signup and view all the answers

    What is the function of the 'rd 101:1' command in the VRF configuration?

    <p>To specify the route distinguisher</p> Signup and view all the answers

    What is the purpose of the 'route-target both 101:1' command in the VRF configuration?

    <p>To specify the route target for import and export</p> Signup and view all the answers

    What is the IP address of the Loopback0 interface?

    <p>12.0.0.3</p> Signup and view all the answers

    How many iBGP sessions are established in the given example?

    <p>2</p> Signup and view all the answers

    What is the VRF name configured in the given example?

    <p>RED</p> Signup and view all the answers

    What is the purpose of a route-target in BGP?

    <p>To control the import and export of routes</p> Signup and view all the answers

    What is carried in BGP updates in an MPLS VPN?

    <p>VPN-IPv4 and VPN-IPv6 routes</p> Signup and view all the answers

    What is the label imposed by PE A to identify the next-hop LSR on the IGP path to PE D?

    <p>96</p> Signup and view all the answers

    What do the LSRs in the core have visibility of?

    <p>Labeled traffic along LSPs</p> Signup and view all the answers

    What is used to identify which VPN routing table to use for the packet?

    <p>The remaining label</p> Signup and view all the answers

    What is the purpose of a VPN ID?

    <p>To define a VPN in a network</p> Signup and view all the answers

    What happens to the packet at the penultimate hop?

    <p>The outer label is popped</p> Signup and view all the answers

    What is the function of PE D in the MPLS-based Layer 3 VPN configuration?

    <p>To use the remaining label to identify which VPN routing table to use for the packet</p> Signup and view all the answers

    How does PE D forward the packet after popping the label?

    <p>PE D forwards the packet to CE green2</p> Signup and view all the answers

    What is the purpose of the IGP in the MPLS-based Layer 3 VPN configuration?

    <p>To forward labeled traffic along LSPs</p> Signup and view all the answers

    What is the purpose of a VRF in an MPLS-VPN configuration?

    <p>To separate customer routing domains</p> Signup and view all the answers

    Why do standard commands like ping, telnet, and traceroute need a new parameter in an MPLS-VPN?

    <p>Because they need to specify the VPN to originate from</p> Signup and view all the answers

    What is the default behavior of a PE in an MPLS-VPN architecture?

    <p>To forward traffic directly to its destination</p> Signup and view all the answers

    What is the purpose of the 'tag-switching ip' command in the interface configuration?

    <p>To enable MPLS on the interface</p> Signup and view all the answers

    Why do some enterprise networks need to change the default behavior of a PE in an MPLS-VPN architecture?

    <p>Because they require a hub-and-spoke configuration</p> Signup and view all the answers

    What is the purpose of the 'neighbor' commands in the BGP configuration?

    <p>To establish iBGP sessions between the PEs</p> Signup and view all the answers

    What is the benefit of using VRFs in an MPLS-VPN configuration?

    <p>To provide a separate routing domain for each customer</p> Signup and view all the answers

    Why is a VRF necessary on a PE device in an MPLS-VPN configuration?

    <p>To separate the customer routing domains</p> Signup and view all the answers

    What is the purpose of the 'tag-switching ip' command in the interface configuration?

    <p>To enable label switching on the interface</p> Signup and view all the answers

    What is the function of a route-distinguisher in BGP?

    <p>To distinguish between routes from different VPNs</p> Signup and view all the answers

    What is the purpose of a VRF in an MPLS-VPN configuration?

    <p>To isolate customer traffic</p> Signup and view all the answers

    What is carried in BGP updates in an MPLS VPN?

    <p>IP routes and labels</p> Signup and view all the answers

    What is the purpose of the 'ip vrf forwarding RED' command?

    <p>To enable VRF forwarding on the interface</p> Signup and view all the answers

    What is the purpose of the 'rd 101:1' command in the VRF configuration?

    <p>To configure the route-distinguisher for the VRF</p> Signup and view all the answers

    How many iBGP sessions are established in the given example?

    <p>2</p> Signup and view all the answers

    What is the VRF name configured in the given example?

    <p>RED</p> Signup and view all the answers

    What is the benefit of using MPLS-VPN over dedicated WAN connections between sites?

    <p>It is more cost-effective and easier to route between sites</p> Signup and view all the answers

    What allows MPLS-VPN to support customer address-space independence?

    <p>The forwarding mechanism that uses a two-label hierarchy</p> Signup and view all the answers

    What is the purpose of the service provider in an MPLS-VPN network?

    <p>To exchange customer routes and carry packets to those routes across its network</p> Signup and view all the answers

    What routing protocol does CE red1 use to advertise the 192.168.4.0/24 prefix to PE A?

    <p>eBGP</p> Signup and view all the answers

    What is the function of PE A in the MPLS-based Layer 3 VPN configuration?

    <p>To exchange customer routes and carry packets to those routes across its network</p> Signup and view all the answers

    What is the intersite IP topology in an MPLS-VPN implementation?

    <p>Arbitrary complexity</p> Signup and view all the answers

    What is the advantage of MPLS-VPN over traditional WAN connections?

    <p>It is more cost-effective and easier to route between sites</p> Signup and view all the answers

    What is the purpose of the two-label hierarchy in MPLS-VPN?

    <p>To support customer address-space independence</p> Signup and view all the answers

    What is the key benefit of an MPLS-VPN service over dedicated WAN connections?

    <p>No architecture change to the customer's network</p> Signup and view all the answers

    What is the main application of MPLS that has caused the most interest?

    <p>Layer 3 VPN</p> Signup and view all the answers

    What connects customer sites in an MPLS-VPN reference architecture?

    <p>PE and CE routers</p> Signup and view all the answers

    What is the function of a PE router in an MPLS-VPN reference architecture?

    <p>To peer with CEs that belong to different customers</p> Signup and view all the answers

    What is a characteristic of an MPLS-VPN service?

    <p>Sites in a VPN can communicate only with other sites in the same VPN</p> Signup and view all the answers

    Why can't a CE-PE link be shared with other customer traffic?

    <p>Because standard IP traffic runs over the link</p> Signup and view all the answers

    What is the purpose of a VRF in an MPLS-VPN configuration?

    <p>To provide a separate routing table for each VPN</p> Signup and view all the answers

    What type of routers exchange routes with service provider edge routers?

    <p>CE routers</p> Signup and view all the answers

    What is the advantage of using MPLS-VPN over dedicated WAN connections?

    <p>Cost-effectiveness</p> Signup and view all the answers

    How do CE devices exchange routes with PE devices?

    <p>Using static or dynamic routing</p> Signup and view all the answers

    What is the primary function of the inner label in MPLS-VPN?

    <p>Identifying the VPN</p> Signup and view all the answers

    What is the result of default MPLS-VPN implementation?

    <p>Full-mesh connectivity</p> Signup and view all the answers

    What is the purpose of the service provider in MPLS-VPN?

    <p>Exchanging customer IP routes</p> Signup and view all the answers

    What is the benefit of MPLS-VPN in terms of routing?

    <p>Easier routing between CEs</p> Signup and view all the answers

    What is the characteristic of intersite IP topology in MPLS-VPN?

    <p>Arbitrarily complex</p> Signup and view all the answers

    What is the protocol used to exchange prefixes and labels between PE devices?

    <p>BGP</p> Signup and view all the answers

    What is the purpose of the routing table for each VPN on a PE router?

    <p>To store the routes of a specific VPN</p> Signup and view all the answers

    How do PE routers announce reachability for each of their attached customer sites?

    <p>Using iBGP</p> Signup and view all the answers

    What happens when PE A needs to find the route to 192.168.3.0?

    <p>It will perform another lookup to find the route</p> Signup and view all the answers

    What is the role of PE C in the MPLS-VPN network?

    <p>It is a provider edge router</p> Signup and view all the answers

    How does PE A identify the next hop for a packet going from CE green1 to CE green2?

    <p>It checks the routing table for the green VPN</p> Signup and view all the answers

    What is the purpose of the label imposed by PE A on the packet going from CE green1 to CE green2?

    <p>To identify the VPN routing table</p> Signup and view all the answers

    What is the topology of the iBGP sessions between the PE routers?

    <p>Full mesh</p> Signup and view all the answers

    How does CE green2 forward IP packets to PE A?

    <p>It forwards IP packets to PE A as it would to any other router</p> Signup and view all the answers

    What is the purpose of the label 96 imposed by PE A?

    <p>To identify the next-hop LSR on the IGP path to PE D</p> Signup and view all the answers

    What is the role of LSR B in the packet flow?

    <p>To remove the outer label</p> Signup and view all the answers

    What is used by PE D to identify which VPN routing table to use for the packet?

    <p>The label 22</p> Signup and view all the answers

    What is the benefit of using a VPN ID in an MPLS VPN?

    <p>It allows for easier definition of a VPN in a network</p> Signup and view all the answers

    What is the characteristic of the LSRs in the core?

    <p>They do not have visibility of the VPN traffic</p> Signup and view all the answers

    What is the role of the IGP in the MPLS VPN?

    <p>It is used to forward labeled traffic along LSPs</p> Signup and view all the answers

    What is the purpose of the VPN routing table?

    <p>To find the outgoing interface and forward the IP packet to CE green2</p> Signup and view all the answers

    What is the relationship between the IGP running on the CE-PE links and the IGP running in the service provider core?

    <p>They are different IGPs</p> Signup and view all the answers

    What might be the reason for a security policy that requires all sites in a certain area to forward traffic through a regional hub?

    <p>To use an expensive virus-checking package for e-mail</p> Signup and view all the answers

    In a hub-and-spoke topology, what is the role of the hub?

    <p>To import routes from all spokes</p> Signup and view all the answers

    What is the purpose of route-targets in MPLS VPNs?

    <p>To configure the hub-and-spoke topology</p> Signup and view all the answers

    What is the characteristic of a hub in a hub-and-spoke topology?

    <p>It imports routes from all spokes</p> Signup and view all the answers

    What is the purpose of a spoke in a hub-and-spoke topology?

    <p>To import routes from the hub</p> Signup and view all the answers

    What is the benefit of using route-targets in MPLS VPNs?

    <p>It simplifies the configuration of hub-and-spoke topologies</p> Signup and view all the answers

    What is the purpose of an extranet in MPLS VPNs?

    <p>To provide a VPN with limited reachability of destinations</p> Signup and view all the answers

    What is the role of PEs in a hub-and-spoke topology?

    <p>To forward traffic between the hub and spokes</p> Signup and view all the answers

    What does PE A use to announce reachability for each of its attached customer sites?

    <p>iBGP</p> Signup and view all the answers

    What is the function of PE C in the given MPLS-VPN configuration?

    <p>To import routes into the routing table used for the red VPN</p> Signup and view all the answers

    How does PE A identify the next hop for a packet going from CE green1 to CE green2?

    <p>By checking the BGP neighbor table</p> Signup and view all the answers

    What is the purpose of the label imposed by PE A on the packet going from CE green1 to CE green2?

    <p>To identify the VPN routing table</p> Signup and view all the answers

    How many iBGP sessions does PE A have in the given example?

    <p>2</p> Signup and view all the answers

    What is the topology of the iBGP sessions between the PEs?

    <p>Full mesh</p> Signup and view all the answers

    What is the purpose of a VRF in an MPLS-VPN configuration?

    <p>To isolate customer traffic</p> Signup and view all the answers

    What is the label imposed by PE A to identify the next-hop LSR on the IGP path to PE D?

    <p>22</p> Signup and view all the answers

    What is the purpose of the 'update-source Loopback0' command in the BGP peer configuration?

    <p>To specify the source IP address of BGP updates</p> Signup and view all the answers

    What is the function of a VRF in an MPLS-VPN configuration?

    <p>To separate customer routing tables</p> Signup and view all the answers

    In an MPLS-VPN network, how does a service provider identify and differentiate between customer routes?

    <p>Using a two-label hierarchy with route-distinguishers</p> Signup and view all the answers

    What is the function of a VRF in an MPLS-VPN configuration?

    <p>To separate customer routes from the service provider's network</p> Signup and view all the answers

    What is the purpose of the 'redistribute connected' command in the VRF configuration?

    <p>To redistribute connected routes into BGP</p> Signup and view all the answers

    What is the purpose of the 'route-target' command in an MPLS-VPN Cisco IOS configuration?

    <p>To import/export routes between VRFs</p> Signup and view all the answers

    What is the purpose of the 'tag-switching ip' command in the interface configuration?

    <p>To enable MPLS VPN on the interface</p> Signup and view all the answers

    Why do standard commands like ping, telnet, and traceroute not work in a VRF?

    <p>Because they use the global routing table</p> Signup and view all the answers

    How do CE devices typically exchange routes with PE devices in an MPLS-VPN network?

    <p>Using dynamic routing protocols such as RIP, eBGP, or OSPF</p> Signup and view all the answers

    What is the purpose of the 'neighbor 12.0.0.2 send-community extended' command in the BGP configuration?

    <p>To send extended community attributes to the BGP peer</p> Signup and view all the answers

    What is the function of the 'rd' command in an MPLS-VPN Cisco IOS configuration?

    <p>To configure the route-distinguisher for a VRF</p> Signup and view all the answers

    What is the benefit of using a VRF in an MPLS-VPN configuration?

    <p>It separates customer routing tables</p> Signup and view all the answers

    What is the purpose of the 'ip vrf forwarding' command in an MPLS-VPN Cisco IOS configuration?

    <p>To associate an interface with a VRF</p> Signup and view all the answers

    What is the function of the 'rd 101:1' command in the VRF configuration?

    <p>To specify the route distinguisher</p> Signup and view all the answers

    What is the benefit of using MPLS-VPN over dedicated WAN connections between sites?

    <p>All of the above</p> Signup and view all the answers

    What is the purpose of the BGP peer configuration in an MPLS-VPN network?

    <p>To advertise customer prefixes to other PEs</p> Signup and view all the answers

    What is the primary function of a route-distinguisher in an MPLS-VPN network?

    <p>To make sure each BGP peer treats the prefixes as belonging to different networks</p> Signup and view all the answers

    Which of the following is true about BGP peer configuration in an MPLS-VPN network?

    <p>Only PE devices with the same VPN and matching route-target import the route</p> Signup and view all the answers

    What is the purpose of a VRF in an MPLS-VPN configuration?

    <p>To separate routing tables for each VPN</p> Signup and view all the answers

    What is the purpose of the route-distinguisher in the given MPLS-VPN configuration?

    <p>To distinguish between different VPNs on the same PE router</p> Signup and view all the answers

    What is required on CE routers in an MPLS-VPN network?

    <p>No VRF is required</p> Signup and view all the answers

    What is the purpose of the 'neighbor 12.0.0.1 remote-as 101' command in the BGP peer configuration?

    <p>To establish an iBGP session with the remote PE router</p> Signup and view all the answers

    What is the purpose of the VRF configuration in the given MPLS-VPN example?

    <p>To define a virtual routing table for the VPN</p> Signup and view all the answers

    What is the purpose of the MPLS-VPN Cisco IOS configuration?

    <p>To deploy a simple MPLS VPN</p> Signup and view all the answers

    What is the benefit of having the same route-distinguisher throughout a VPN?

    <p>It provides operational simplicity</p> Signup and view all the answers

    What is the purpose of the 'ip vrf forwarding RED' command in the CE-PE link configuration?

    <p>To add the CE-PE link to the VRF</p> Signup and view all the answers

    What is populated using information from VRFs?

    <p>The LFIBs</p> Signup and view all the answers

    What is the purpose of the 'tag-switching ip' command in the interface configuration?

    <p>To enable MPLS on the interface</p> Signup and view all the answers

    What is the purpose of a VRF in a CE router?

    <p>It is not required on CE routers</p> Signup and view all the answers

    What is carried in BGP updates in an MPLS VPN?

    <p>Both IP prefixes and MPLS labels</p> Signup and view all the answers

    What is the purpose of the 'route-target both 101:1' command in the VRF configuration?

    <p>To import and export routes to and from the VRF</p> Signup and view all the answers

    How many iBGP sessions are established in the given example?

    <p>2</p> Signup and view all the answers

    Study Notes

    MPLS VPN Reference Architecture

    • /MPLS VPN is a peer architecture where customer edge (CE) routers exchange routes with service provider edge routers (PE)
    • CE routers connect to PE routers, which are connected by Label Switching Routers (LSRs)
    • A single PE can peer with CEs that belong to different customers
    • CEs can also peer with different PEs that belong to the same or different service providers
    • Sites in a VPN can communicate only with other sites in the same VPN

    MPLS-VPN Reference Architecture

    • Standard IP traffic runs over the CE-PE link, so this link cannot be shared with other customer traffic
    • CE and PE do not exchange labels or labeled packets
    • MPLS-VPN architecture provides full-mesh connectivity between sites, despite each site having only one link into the service provider cloud
    • Intersite IP topology can be of arbitrary complexity

    Routing in an MPLS VPN Network

    • MPLS-VPN model makes it easier to route between CEs compared to dedicated WAN connections
    • Service provider needs to exchange customer IP routes and carry packets to those routes across its network
    • MPLS provides a solution that supports customer address-space independence using a two-label hierarchy
    • Inner label identifies the VPN and the outer label identifies the destination PE device
    • RFC 2547 mandates the use of BGP to exchange prefixes and labels between PE devices

    MPLS-VPN Routing

    • CEs can use static or dynamic routing (RIP, eBGP, or OSPF) to exchange routes with a PE
    • PE imports prefixes announced by the CE into the route table for this VPN
    • Each VPN has its own routing table
    • PE uses iBGP to announce reachability for each of its attached customer sites
    • PEs are in a full iBGP mesh and can run many different VPNs

    MPLS-VPN Attributes

    • Each VPN on a Cisco router has dedicated interfaces, routing table, local name, and numeric ID
    • Rules determine how VPN routes are advertised to peer routers
    • Route reachability is established through the selective import of BGP routes
    • Several new extended attributes have been added to BGP in accordance with RFC 2547

    BGP Attributes

    • Route-target: a numeric value associated with all routes exported to BGP peers
    • Route-target export value must match the import value at the receiving device
    • Route-distinguisher: a BGP attribute that is appended to private routes to make them globally unique

    MPLS-VPN Cisco IOS Configuration

    • VRF configuration: defines the VPN routing table and imports routes
    • Route-target and RD values must match, but VRF names don't have to
    • Egress CE-PE link configuration: defines the IP address and routing for the CE-PE link

    MPLS-VPN Reference Architecture

    • Even with a single link to the service provider cloud, MPLS-VPN architecture allows for full-mesh connectivity between sites.
    • The intersite IP topology can be arbitrarily complex, but MPLS-VPN implementations default to full mesh and must be constrained to provide a more hierarchical model.
    • MPLS-VPN makes it easier to route between CEs compared to using dedicated WAN connections between sites and routing over point-to-point networks.

    MPLS-VPN Architecture

    • MPLS-VPN uses a two-label hierarchy, where the inner label identifies the VPN and the outer label identifies the destination PE device.
    • RFC 2547 mandates the use of BGP to exchange prefixes and labels between PE devices.
    • Customer address-space independence is achieved using a forwarding mechanism.

    Routing in an MPLS VPN Network

    • CE devices can use static or dynamic routing (RIP, eBGP, or OSPF) to exchange routes with a PE.
    • The packet must travel across the MPLS network, so PE A imposes another label that identifies the next-hop LSR on the IGP path to PE D.
    • Each LSR in the core swaps labels and forwards the packet as normal toward PE D.
    • The penultimate hop pops the outer label, and PE D uses the remaining label to identify which VPN routing table to use for the packet.

    Packet Flow in MPLS-VPN Network

    • LSRs have no visibility of the VPN traffic and forward labeled traffic along LSPs established by the routing protocol running in the service provider core.
    • The IGP running on the CE-PE links can be different from the IGP running on the core.

    MPLS-VPN Attributes

    • Defining an MPLS VPN is harder than expected, and a VPN ID has been introduced to address this problem.
    • The underlying network topology is the same as used in the examples.

    MPLS-VPN Configuration

    • PE configuration involves setting up a VRF for the VPN with route-distinguisher and route-target values.
    • Each CE-PE link needs to be added to the VRF.
    • iBGP is used to establish sessions to peers.
    • The VPNv4 address-family establishes the peers as being MPLS-VPN savvy.

    LSR Configuration

    • LSR configuration is straightforward and involves setting up core-facing links.

    PE Configuration

    • PE configuration involves setting up a VRF for the VPN with route-distinguisher and route-target values that match the other side of the network.
    • Egress CE-PE link and core-facing links need to be configured.

    VRF Options

    • Ping, telnet, and traceroute have VRF options to make them usable between PEs.
    • Standard commands don't work because they use the global routing table, which is different from the VRF.
    • VRF represents an entirely private routing space.

    MPLS VPN Reference Architecture

    • MPLS VPN is a Layer 3 VPN that allows for full-mesh connectivity between customer sites without point-to-point connections.
    • Customer Edge (CE) routers connect to Service Provider Edge (PE) routers, which are connected by Label Switching Routers (LSRs).
    • A single PE can peer with multiple CEs from different customers.
    • CE-PE links are standard IP traffic and cannot be shared with other customer traffic.

    Routing in an MPLS VPN Network

    • Customer routes are advertised in an MPLS VPN network using Border Gateway Protocol (BGP).
    • CE routers can use static or dynamic routing (RIP, eBGP, or OSPF) to exchange routes with a PE.
    • Each VPN has its own routing table, and PE routers use iBGP to announce reachability for each attached customer site.
    • PE routers are in a full iBGP mesh and can run multiple VPNs.

    MPLS-VPN Packet Flow

    • When traffic needs to go between sites, the CE forwards IP packets to the PE as it would to any other router.
    • The PE identifies the next hop (PE) for the packet as a BGP neighbor and imposes a label that identifies the VPN routing table.
    • The packet is then forwarded across the MPLS network, where each LSR swaps labels and forwards the packet towards the next hop.
    • The penultimate hop pops the outer label, and the final PE uses the remaining label to identify the VPN routing table and forward the packet to the CE.

    MPLS-VPN Attributes

    • Defining an MPLS VPN requires a VPN ID, which is a unique identifier for a VPN in a network.
    • MPLS VPNs can be deployed as hub-and-spoke topologies using route-targets.
    • Route-targets are used to control the flow of traffic between sites in a VPN.

    VRF (Virtual Routing and Forwarding)

    • A VRF is a virtual routing table used to separate customer traffic in an MPLS VPN.
    • Each VRF has its own routing table and is used to forward traffic between sites in a VPN.

    MPLS-VPN Configuration

    • Cisco IOS configuration for MPLS VPN involves defining the VRF, route-targets, and importing/exporting routes between VPNs.
    • Examples of configuration commands are shown for hub-and-spoke topologies and extranets.

    MPLS-VPN Configuration

    • A CE uses RIPv2 to announce prefixes to a PE.
    • The PE imports the prefixes into the route table for its VPN.
    • Each VPN has its own routing table.
    • A PE uses iBGP to announce reachability for each of its attached customer sites.

    PE Configuration

    • A PE has its own routing table for each VPN.
    • A PE announces itself as the next hop for routes.
    • A PE identifies the next hop (another PE) for a packet as a BGP neighbor.
    • A PE imposes a label that identifies the VPN routing table to the next hop PE.

    MPLS-VPN Operation

    • Traffic between sites is forwarded by CEs to the PE as it would to any other router.
    • A PE announces routes to all its PE peers, but only those with the same VPN and matching route-target import it.
    • The route-distinguisher (RD) is included in the routing exchange to make sure that each BGP peer treats the prefixes as belonging to different networks.

    VRFs

    • VRFs are populated by routing processes associated with each VPN.
    • In Cisco IOS, there are independent OSPF processes for each VPN, but BGP is a single process across the whole router.
    • LFIBs are populated using information from VRFs.
    • No VRFs are required on CE routers.

    Cisco IOS Configuration

    • The configuration extracts are necessary to deploy a simple MPLS VPN.
    • A VRF is set up for the VPN with a route-distinguisher, route-target, and interface configurations.
    • iBGP is configured to announce reachability for each of its attached customer sites.

    Full-Mesh Configuration

    • MPLS-VPN architecture provides full-mesh configuration by default.
    • A PE forwards traffic directly to its destination.
    • The intersite IP topology can be of arbitrary complexity.
    • MPLS-VPN implementations default to full mesh and must be constrained to provide a more hierarchical connectivity model.

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    Related Documents

    W4_JTO_Ph2_Datacom_IT-part-6.pdf

    Description

    Learn about MPLS VPN reference architecture, routing, attributes, VRF, and Cisco IOS configuration. This chapter covers the configuration of MPLS based Layer 3 VPN on Cisco Routers.

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