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Questions and Answers

What is the customer network in MPLS VPN architecture?

A CE router

A customer-controlled domain consisting of devices or routers (correct)

A provider-controlled domain

A shared infrastructure between customers

What is the role of a CE router in MPLS VPN architecture?

To support MPLS

To sense the existence of any VPN

To control traffic routing between sites

To interface with the service provider network (correct)

What is the provider network in MPLS VPN architecture?

A CE router

A customer-controlled domain consisting of devices or routers

A shared infrastructure between customers

A provider-controlled domain consisting of provider edge and provider core routers (correct)

What is the role of a PE router in MPLS VPN architecture?

To connect multiple CEs to the network Signup and view all the answers

Where does all VPN processing occur in an MPLS network?

On PE routers Signup and view all the answers

What is the primary function of the provider network in MPLS VPN architecture?

To provide customer traffic isolation Signup and view all the answers

What type of device can a CE router be in MPLS VPN architecture?

A router, a switch, or a host Signup and view all the answers

How many interfaces can a CE router have connected to a service provider network?

One or more Signup and view all the answers

What is the primary function of P routers in an MPLS VPN architecture?

To perform label switching of packets Signup and view all the answers

What is the main purpose of configuring multiprotocol BGP between PE routers?

To enable scaling the network to a large number of customer VPNs Signup and view all the answers

What is the function of a VRF?

To define the connectivity requirements and protocols for each customer site Signup and view all the answers

What is contained in a VRF?

A CEF forwarding table and routes pertaining to a specific VPN Signup and view all the answers

How many interfaces can be bound to a VRF?

The number of interfaces that can be bound to a VRF is only limited by the number of interfaces on the router Signup and view all the answers

What is true about an interface that is part of a VRF?

It must support CEF switching Signup and view all the answers

What is not a component of a VRF?

A list of interfaces that are not part of the VRF Signup and view all the answers

What is the role of PE routers in an MPLS VPN architecture?

To exchange IPv4 routes with connected CE routers using individual routing protocol contexts Signup and view all the answers

What information does an IGP provide to iBGP in an MPLS VPN?

NLRI information Signup and view all the answers

Which two IGPs are currently supported by Cisco in an MPLS provider network?

OSPFv2 and ISIS Signup and view all the answers

What is one of the primary reasons for choosing BGP to carry customer routing information?

Scalability Signup and view all the answers

What is the primary purpose of the VPN label in an MPLS VPN?

To assign a label to the customer routes Signup and view all the answers

What is an MP-eBGP session used for in an MPLS VPN?

To exchange VPNv4 routes between AS boundaries Signup and view all the answers

What is the purpose of route targets in an MPLS VPN?

To identify VPN membership of the routes Signup and view all the answers

How are route targets implemented in an MPLS VPN?

Using extended BGP communities Signup and view all the answers

What is the export route target used for in an MPLS VPN?

To identify the VPN membership of the site Signup and view all the answers

What is appended to the data packet by PE2-AS1 in Step 2?

VPN label V1 and LDP label L2 Signup and view all the answers

What happens to the LDP label L2 in Step 3?

It is swapped with L1 Signup and view all the answers

What does P1-AS1 do with the top label in Step 4?

Pops the top label Signup and view all the answers

What is used to forward the packet through the MPLS domain?

The next-hop label mapping Signup and view all the answers

What is the protocol used to advertise VPN routes in MPLS L3VPN?

BGP Signup and view all the answers

What is a key benefit of MPLS L3VPN?

Scalability Signup and view all the answers

What is the purpose of MPLS VPN?

To create virtual private networks Signup and view all the answers

What is not done to the VPN label until it reaches the egress PE router?

It is touched Signup and view all the answers

What is the purpose of MP_REACH_NLRI in BGP?

To carry the set of reachable destinations together with the next-hop information Signup and view all the answers

What is the purpose of MP_UNREACH_NLRI in BGP?

To carry the set of unreachable destinations Signup and view all the answers

What is an address family identifier (AFI) in BGP?

An identity of the network layer protocol associated with the network address Signup and view all the answers

What is the role of the PE router in MPLS VPN?

To perform all the functions of an Edge LSR and implement a routing protocol with connected CE routers Signup and view all the answers

What is the purpose of LDP on the PE router?

To assign labels to prefixes learned from CE routers Signup and view all the answers

What is the purpose of MP-iBGP updates?

To propagate prefixes learned from CE routers as VPNv4 prefixes Signup and view all the answers

What is the purpose of the P router in MPLS VPN?

To run an IGP and MPLS enabled Signup and view all the answers

What is the purpose of LDP on the P router?

To label assignment and distribution Signup and view all the answers

What is the primary benefit of MPLS VPN architecture over traditional VPN models?

Improved scalability and peer-to-peer model implementation Signup and view all the answers

In an MPLS VPN, how do customer sites exchange routing information?

By exchanging Layer 3 customer routing information with the MPLS-enabled SP IP backbone Signup and view all the answers

What is a key advantage of MPLS VPN in terms of address space management?

MPLS VPN accommodates customers using overlapping address spaces Signup and view all the answers

What is the role of MPLS-enabled SP IP backbone in an MPLS VPN?

It provides connectivity between customer sites and the provider network Signup and view all the answers

How do PE routers handle customer traffic in an MPLS VPN?

Customer traffic is isolated on the same PE router that provides connectivity into the service provider's network for multiple customers Signup and view all the answers

What is the primary purpose of MPLS VPN architecture?

To implement a scalable peer-to-peer model for customer traffic Signup and view all the answers

What is a key characteristic of an MPLS VPN domain?

It consists of the customer network and the provider network Signup and view all the answers

What is the purpose of the MPLS VPN backbone in an MPLS VPN architecture?

To forward data between customer sites using the MPLS-enabled SP IP backbone Signup and view all the answers

What is the purpose of the top label in the label stack in MPLS VPN?

To identify the next-hop address of the ingress PE router Signup and view all the answers

What happens to the VPN label until it reaches the egress PE router?

It is kept intact Signup and view all the answers

What is the purpose of the second label in the label stack in MPLS VPN?

To identify the VPN label assigned by the egress PE router Signup and view all the answers

What is the role of P routers in MPLS VPN data plane operation?

To perform label switching on the LDP-assigned label toward the egress PE router Signup and view all the answers

What is the purpose of the VRF table in MPLS VPN data plane operation?

To perform another IP lookup to identify the next hop toward the destination Signup and view all the answers

What is the purpose of the egress PE router in MPLS VPN data plane operation?

To identify the VPN label assigned with a VRF and forward the packet Signup and view all the answers

What happens to the packet when it reaches the egress PE router in MPLS VPN data plane operation?

The VPN label is removed and the packet is forwarded to the CE router Signup and view all the answers

What is the purpose of the label stack in MPLS VPN data plane operation?

To enable label switching and VPN label assignment Signup and view all the answers

What is the primary purpose of configuring multiprotocol BGP between PE routers?

To carry customer routes and enable scaling to a large number of VPNs Signup and view all the answers

What is the function of a VRF on a PE router?

To isolate customer VPNs and maintain a VRF-specific routing table Signup and view all the answers

What is contained in a VRF on a PE router?

A VRF-specific routing table, CEF table, and list of interfaces Signup and view all the answers

What is the limitation on the number of interfaces that can be bound to a VRF?

Limited by the number of interfaces on the router Signup and view all the answers

What is true about an interface that is part of a VRF?

It can be associated with only one VRF Signup and view all the answers

What is the primary benefit of using multiprotocol BGP between PE routers?

Scales to a large number of customer VPNs Signup and view all the answers

What is the purpose of a VRF-specific CEF forwarding table?

To define the connectivity requirements and protocols for each customer site Signup and view all the answers

What information does a VRF contain?

VPN identifiers, VPN membership information, IP routing table, CEF table, and list of interfaces Signup and view all the answers

What is the primary function of MP-BGP in an MPLS VPN?

To exchange VPNv4 routes between PE routers Signup and view all the answers

What is the purpose of a Route Distinguisher (RD) in an MPLS VPN?

To differentiate between customer routes with the same IP address Signup and view all the answers

What is the purpose of a Route Target (RT) in an MPLS VPN?

To advertise VPNv4 routes to other PE routers Signup and view all the answers

What is the result of not configuring a Route Target (RT) on a VRF?

The VRF will not import any routes Signup and view all the answers

What is the purpose of VPN label assignment in an MPLS VPN?

To forward VPN traffic at the data plane Signup and view all the answers

What is the result of not configuring a Route Distinguisher (RD) on a VRF?

The VRF will not be able to differentiate between customer routes Signup and view all the answers

What is the purpose of VPNv4 route propagation in an MPLS VPN?

To exchange VPNv4 routes between PE routers Signup and view all the answers

What is the topology design consideration for an MPLS VPN?

Partial mesh topology between PE routers Signup and view all the answers

Which routers in the MPLS VPN architecture connect sites belonging to a customer?

PE routers Signup and view all the answers

Where does VPN processing occur in an MPLS network?

On PE routers Signup and view all the answers

What is the primary function of the provider network in MPLS VPN architecture?

To control traffic routing between sites Signup and view all the answers

What is the role of a CE router in MPLS VPN architecture?

To connect customer devices to the provider network Signup and view all the answers

How many customer networks can a PE router connect?

Multiple Signup and view all the answers

What is the purpose of a PE router in MPLS VPN architecture?

To connect customer edge routers to the provider network Signup and view all the answers

What is the role of P routers in MPLS VPN architecture?

To forward traffic between PE routers Signup and view all the answers

What is the primary purpose of configuring multiprotocol BGP between PE routers?

To advertise customer routes Signup and view all the answers

What was the limitation of the initial implementation of the VPN model?

Higher equipment costs Signup and view all the answers

What is a feature of the MPLS-based VPN model?

Customers can use overlapping address spaces Signup and view all the answers

What is a key benefit of the MPLS VPN architecture?

Scalable peer-to-peer model implementation Signup and view all the answers

How do customer sites exchange routing information in an MPLS VPN?

Through the MPLS-enabled SP IP backbone Signup and view all the answers

What is a characteristic of the MPLS VPN domain?

Combination of customer and provider networks Signup and view all the answers

How do PE routers handle customer traffic in an MPLS VPN?

By isolating customer traffic on the same PE router Signup and view all the answers

What is the primary purpose of the MPLS VPN architecture?

To implement a scalable peer-to-peer VPN model Signup and view all the answers

What is an advantage of MPLS VPN architecture over traditional VPN models?

Easier address space management Signup and view all the answers

Which component of the MPLS VPN architecture is responsible for controlling traffic routing between sites belonging to a customer and ensuring customer traffic isolation?

Provider network Signup and view all the answers

What is the primary function of the CE routers in the MPLS VPN architecture?

To connect customer sites to the provider edge routers Signup and view all the answers

What is a characteristic of the provider network in the MPLS VPN architecture?

It is a shared infrastructure Signup and view all the answers

Where is the VPN processing done in an MPLS network?

On the PE routers Signup and view all the answers

What is true about the PE routers in the MPLS VPN architecture?

They interface with the CE routers Signup and view all the answers

What is the main purpose of the PE routers in the MPLS VPN architecture?

To provide VPN processing and connected one or more CEs to the network Signup and view all the answers

What is a characteristic of the CE routers in the MPLS VPN architecture?

They can be a router, a switch, or a host Signup and view all the answers

What is true about the customer network in the MPLS VPN architecture?

It is a customer-controlled domain Signup and view all the answers

What does the SoO extended community uniquely identify in an MPLS VPN?

The customer site Signup and view all the answers

What is the purpose of route targets in an MPLS VPN?

To implement complex VPN topologies Signup and view all the answers

What is an implementation of a MPLS VPN in which all VPN sites belonging to a customer can speak to all other sites in the same customer domain called?

Intranet VPN Signup and view all the answers

What does RFC 2283 define?

Extensions to BGP-4 that enable BGP-4 to carry information for multiple network layer protocols Signup and view all the answers

What is the purpose of address families in MP-BGP?

To enable the transport of VPNv4 routes with extended community attributes Signup and view all the answers

What is a variant of extranet VPN?

Central services VPN Signup and view all the answers

What is the primary function of MP-BGP?

To enable the transport of VPNv4 routes with extended community attributes Signup and view all the answers

What is the purpose of SoO filtering?

To prevent routing loops in complex and mixed network topologies Signup and view all the answers

What is the purpose of the RT values in an MPLS VPN?

To implement complex VPN topologies Signup and view all the answers

Where is the VPN label only understood in an MPLS VPN?

On the PE router that is directly connected to the CE router Signup and view all the answers

What is the purpose of the SoO attribute in an MPLS VPN?

To prevent routing loops Signup and view all the answers

What is carried by MP-BGP in an MPLS VPN?

The VPNv4 prefix (IPv4 prefix + prepended RD) in addition to the BGP route target extended community Signup and view all the answers

What is stored in the VRF table for Customer A?

The received MP-BGP routes Signup and view all the answers

What is propagated to CE2-A?

The received MP-BGP routes Signup and view all the answers

What is learned from the IGP for MPLS VPN implementation?

The next hops on PE routers Signup and view all the answers

What is used to prevent routing loops?

The SoO attribute Signup and view all the answers

What is the primary function of MP_REACH_NLRI in BGP?

To carry the set of reachable destinations together with the next-hop information Signup and view all the answers

What is the role of the PE router in MPLS VPN?

To implement a routing protocol with connected CE routers per virtual routing table Signup and view all the answers

What is the purpose of an address family identifier (AFI) in BGP?

To identify the network layer protocol associated with the network address Signup and view all the answers

What is the primary function of the P router in MPLS VPN?

To run an IGP and MPLS-enabled Signup and view all the answers

What is the purpose of LDP on the P router?

To assign labels to destinations Signup and view all the answers

What is the primary function of MP-iBGP updates?

To propagate prefixes learned from CE routers as VPNv4 prefixes Signup and view all the answers

What is the purpose of MP_UNREACH_NLRI in BGP?

To carry the set of unreachable destinations Signup and view all the answers

What is the primary function of the PE router in terms of label assignment and distribution?

To assign labels to destinations using LDP Signup and view all the answers

What is the purpose of PE1-AS1 sending an LDP reply to P1-AS1?

To request a label from its downstream neighbor Signup and view all the answers

What is the purpose of P1-AS1 using the implicit-null label received from PE1-AS1?

To use it as its outbound label value Signup and view all the answers

In an MPLS VPN, what is the purpose of Route Targets (RTs)?

To identify the VPN membership of the routes learned from a particular site Signup and view all the answers

What is the purpose of PE1-AS1 translating the VPNv4 update to IPv4?

To insert the route in the VRF for Customer A Signup and view all the answers

What is the purpose of P2-AS1 sending the label value to PE2-AS1 via an LDP reply?

To forward the packet through the MPLS domain Signup and view all the answers

What is the purpose of MP-BGP updates in an MPLS VPN?

To exchange VPNv4 routes between AS boundaries Signup and view all the answers

What happens to the VPN label until it reaches the egress PE router?

It remains unchanged Signup and view all the answers

What is required for packet forwarding in an MPLS VPN?

The PE router that assigns the VPN label must be the same as the router specified as the next hop in the incoming BGP update Signup and view all the answers

What is the primary reason for choosing BGP to carry customer routing information in an MPLS VPN?

To improve scalability Signup and view all the answers

What is the purpose of the VRF configured on PE1-AS1?

To insert the route in the VRF for Customer A Signup and view all the answers

What is the role of LDP in MPLS VPN?

To allocate labels to prefixes Signup and view all the answers

What is the purpose of VPNv4 address in an MPLS VPN?

To enable overlapping address ranges with multiple customers Signup and view all the answers

What is the purpose of the top label in the label stack in MPLS VPN?

To forward the packet through the MPLS domain Signup and view all the answers

What is the purpose of MP-iBGP session in an MPLS VPN?

To establish BGP sessions between PE routers in a single AS Signup and view all the answers

What is the purpose of MP-BGP updates in MPLS VPN?

To advertise VPN routes between PE routers Signup and view all the answers

What is the role of IGP in an MPLS VPN?

To provide NLRI information for iBGP if both PE routers are in the same AS Signup and view all the answers

What happens to the VPN label until it reaches the egress PE router?

It is kept intact Signup and view all the answers

What is the purpose of the second label in the label stack?

To identify the VRF table for aggregate VPN routes Signup and view all the answers

What is the purpose of VPN label assignment in an MPLS VPN?

To assign a VPN label to incoming packets Signup and view all the answers

What is the role of P routers in MPLS VPN data plane operation?

They perform label switching on the LDP-assigned label toward the egress PE router Signup and view all the answers

What is the purpose of the VRF table in MPLS VPN data plane operation?

To identify the next hop toward the destination Signup and view all the answers

What is the role of the egress PE router in MPLS VPN data plane operation?

It identifies the VPN label assigned with a VRF and either forwards the IP packet toward the CE router or performs another IP lookup in the VRF table Signup and view all the answers

What is the purpose of label stacking in MPLS VPN data plane operation?

To enable the egress PE router to identify the VPN label and perform IP lookup Signup and view all the answers

What is the role of the ingress PE router in MPLS VPN data plane operation?

It labels the incoming IP packet for a remote VPN destination with two labels Signup and view all the answers

What is the purpose of the Route Target (RT) in an MPLS VPN?

To implement complex VPN topologies and selective route importing Signup and view all the answers

What is the purpose of the Site of Origin (SoO) attribute in MPLS VPN?

To prevent routing loops Signup and view all the answers

What is carried by MP-BGP in an MPLS VPN?

The VPNv4 prefix in addition to the BGP route target extended community Signup and view all the answers

What happens to the VPN label until it reaches the egress PE router?

It is not changed or modified Signup and view all the answers

What is the purpose of the RD value in an MPLS VPN?

To prepend the IPv4 prefix and make it a VPNv4 prefix Signup and view all the answers

What is the purpose of MP-iBGP updates in an MPLS VPN?

To redistribute received MP-BGP routes into the VRF PE-CE routing processes Signup and view all the answers

What is the primary function of the PE router in an MPLS VPN?

To store the received MP-BGP routes in the appropriate VRF table Signup and view all the answers

What is propagated to CE2-A after the PE router receives the MP-BGP update?

The route Signup and view all the answers

What is the primary function of the PE router in an MPLS L3VPN?

To advertise VPN routes using BGP Signup and view all the answers

What is used to forward packets through the MPLS domain?

The next-hop label mapping Signup and view all the answers

What happens to the VPN label until it reaches the egress PE router?

It is not touched Signup and view all the answers

What is the protocol used to advertise VPN routes in MPLS L3VPN?

BGP Signup and view all the answers

What is the key benefit of MPLS L3VPN?

Scalability and flexibility Signup and view all the answers

What is the purpose of MPLS VPN?

To create virtual private networks (VPNs) Signup and view all the answers

What is the role of the P router in an MPLS VPN?

To forward traffic between PE routers Signup and view all the answers

What is the purpose of the top label in the label stack in MPLS VPN?

To forward the packet to the next hop Signup and view all the answers

Study Notes

MPLS VPN Architecture

The main components of MPLS VPN architecture are:
- Customer network: a customer-controlled domain consisting of devices or routers spanning multiple sites belonging to the customer.
- CE routers: routers in the customer network that interface with the service provider network.
- Provider network: a provider-controlled domain consisting of provider edge and provider core routers that connect sites belonging to the customer on a shared infrastructure.
- PE routers: routers in the provider network that interface or connect to the customer edge routers in the customer network.

Virtual Routing and Forwarding Tables (VRFs)

VRFs are used to achieve customer isolation on the PE router.
A VRF is similar to a global routing table, except that it contains all routes pertaining to a specific VPN.
A VRF contains:
- An IP routing table
- A CEF table
- A list of interfaces that are part of the VRF
- A set of rules defining routing protocol exchange with attached CE routers (routing protocol contexts)
- VPN identifiers and VPN membership information (RD and RT)

Packet Forwarding in MPLS VPN

Packet forwarding in an MPLS VPN mandates that the router specified as the next hop in the incoming BGP update is the same router that assigns the VPN label.
The PE router must run an IGP that provides NLRI information for iBGP if both PE routers are in the same AS.
MP-BGP is responsible for assignment of a VPN label.

Route Targets (RTs)

RTs are additional identifiers used in the MPLS VPN domain to identify the VPN membership of the routes learned from a particular site.
RTs are implemented by the use of extended BGP communities in which the higher order 16 bits of the BGP extended community are encoded with a value corresponding to the VPN membership of the specific site.

Multiprotocol BGP (MP-BGP)

MP-BGP is used to carry customer routing information between PE routers.
MP-BGP enables the use of VPNv4 address in an MPLS VPN router environment that enables overlapping address ranges with multiple customers.
An MP-BGP session between PE routers in a single BGP AS is called an MP-iBGP session.
If the VPN extends beyond a single AS, VPNv4 routes will be exchanged between AS at the AS boundaries using an MP-eBGP session.

MPLS VPN Operation

The PE router, in essence, is an Edge LSR and performs all the functions of an Edge LSR.
The PE router requires LDP for label assignment and distribution as well as to forward labeled packets.
The PE router implements a routing protocol (or static routes) with connected CE routers per virtual routing table and requires MP-BGP to propagate prefixes learned from CE routers as VPNv4 prefixes in MP-iBGP updates to other PE routers along with the VPN label.

Data Plane Forwarding

The data plane forwarding process involves the following steps:
1. The CE router originates a data packet and forwards it to the PE router.
2. The PE router appends the VPN label and LDP label and forwards the packet to the P router.
3. The P router swaps the LDP label and forwards the packet to the next P router.
4. The process continues until the packet reaches the egress PE router, where the VPN label is popped and the packet is forwarded to the CE router.
The key to understanding the operation of MPLS VPN is that the VPN label is never touched until it reaches the egress PE router toward the FEC.

MPLS VPN Architecture and Terminology

MPLS VPN architecture provides optimal routing for traffic belonging to a customer between sites, accommodating customers with overlapping address spaces.
The architecture consists of customer network, provider network, CE routers, and PE routers.
CE routers interface with the service provider network, and PE routers interface with customer edge routers.

Components of MPLS VPN

Customer network: a customer-controlled domain consisting of devices or routers spanning multiple sites.
CE routers: routers in the customer network that interface with the service provider network.
Provider network: a provider-controlled domain consisting of provider edge and provider core routers.
PE routers: routers in the provider network that interface with customer edge routers.

MPLS VPN Data Plane Operation

MPLS VPN data plane operation involves the usage of the label stack, where the top label points to the egress PE router's next-hop address, and the second label points to the VPN label.
The ingress PE router labels the incoming IP packet with two labels, and the P routers perform label switching towards the egress PE router.
The egress PE router identifies the VPN label and either forwards the IP packet towards the CE router or performs another IP lookup in the VRF table.

VRF (Virtual Routing and Forwarding Table)

VRF is used for customer isolation on the PE router, similar to maintaining multiple dedicated routers for customers.
VRF contains all routes pertaining to a specific VPN, as well as a VRF-specific CEF forwarding table and routing protocol contexts.
The function of a VRF is similar to a global routing table, except that it contains routes specific to a VPN.

MPLS VPN Benefits

MPLS VPN provides a scalable peer-to-peer model, allowing for efficient deployment of VPN architectures.
It accommodates customers with overlapping address spaces, eliminating the need for IP address assignment or NAT implementation.
MPLS VPN provides optimal routing for traffic belonging to a customer between sites, ensuring efficient traffic routing and forwarding.

MPLS VPN Architecture and Terminology

MPLS VPN architecture allows for efficient deployment of scalable peer-to-peer models, overcoming the limitations of traditional peer-to-peer models.
Edge routers in the MPLS VPN architecture carry customer routing information, providing optimal routing for inter-site traffic.
MPLS VPN accommodates customers with overlapping address spaces, unlike traditional peer-to-peer models.

MPLS VPN Components

Customer network: a customer-controlled domain consisting of devices or routers spanning multiple sites.
CE (Customer Edge) routers: routers in the customer network that interface with the service provider network.
Provider network: a provider-controlled domain consisting of provider edge and provider core routers that connect sites belonging to a customer.
PE (Provider Edge) routers: routers in the provider network that interface with the customer edge routers in the customer network.

MPLS VPN Operation

PE routers assign a VPN label to each prefix learned from the connected CE router's IGP process within a VRF.
MP-BGP (Multiprotocol Border Gateway Protocol) process carries the VPNv4 prefix (IPv4 prefix + prepended RD) in addition to the BGP route target extended community.
The VPN label is only understood by the egress PE (data plane) that is directly connected to the CE router advertising the prefix.

MPLS VPN Route Target (RT)

RT values are used to implement complex VPN topologies in which a single site can be part of more than one VPN.
RT values can also be used to perform selective route importing into a VRF when VPNv4 routes are learned in MP-iBGP updates.

Site of Origin (SoO) extended community attribute

SoO attribute is used to identify the specific site from which the PE learns the route and prevents routing loops.
SoO filtering manages MPLS VPN traffic and prevents routing loops from occurring in complex and mixed network topologies.

MPLS VPN Implementation

Simple VPN implementation (intranet VPN): all VPN sites belonging to a customer can speak to all other sites in the same customer domain.
Extranet VPN: certain sites that are part of one customer's domain are also accessible by other customers' VPN sites.
Variants of extranet VPN: network management VPN, central services VPN, and Internet access VPN.

Address Families and MP-BGP

MP-BGP enables BGP-4 to carry information for multiple network layer protocols.
Address family is a defined network layer protocol.
Address family identifier (AFI) carries an identity of the network layer protocol associated with the network address in the multiprotocol attributes in BGP.

PE Router Functions

PE router performs all the functions of an Edge LSR (Label Switching Router).
PE router requires LDP for label assignment and distribution as well as forward labeled packets.
PE router implements a routing protocol (or static routes) with connected CE routers per virtual routing table and requires MP-BGP to propagate prefixes learned from CE routers as VPNv4 prefixes in MP-iBGP updates to other PE routers along with the VPN label.

MPLS VPN Architecture

In an MPLS VPN, each prefix learned from a connected CE router's IGP process within a VRF is assigned a VPN label (3 bytes) by the PE router's MP-BGP process.
MP-BGP carries the VPNv4 prefix (IPv4 prefix + prepended RD) and BGP route target extended community.

Route Targets (RTs)

RTs are additional identifiers used in MPLS VPN to identify VPN membership of routes learned from a particular site.
RTs are implemented using extended BGP communities, where the higher order 16 bits of the BGP extended community (64 total bits) are encoded with a value corresponding to the VPN membership of the specific site.
The export route target is used to identify VPN membership and is associated with each VRF.

MPLS VPN Data Plane Operation

Packet forwarding in an MPLS VPN requires that the router specified as the next hop in the incoming BGP update is the same router that assigns the VPN label.
The label stack is used, where the top label is assigned for the egress PE router's (data plane) next-hop address, and the second label is the VPN label assigned by the egress PE router connected to the CE router advertising the prefix.
The second label in the stack points to an outgoing interface whenever the CE router is the next hop of the VPN route.
The second label in the stack points to the VRF table for aggregate VPN routes, VPN routes pointing to null interface, and routes for directly connected VPN interfaces.

Data Plane Forwarding

When data is forwarded to a specific prefix belonging to a VPN across the MPLS-enabled core, the top label in the label stack is swapped as the packet traverses the backbone.
The VPN label is kept intact and is removed only in the egress/downstream PE router.
The resulting prefix is associated with an outgoing interface belonging to a specific VRF on the router depending on the value in the VPN label.

Key Steps in Data Plane Forwarding

CE2-A originates a data packet with a source address and destination.
PE2-AS1 receives the data packet and appends the VPN label and LDP label and forwards the packet to P2-AS1.
P2-AS1 receives the data packet and swaps the LDP label.
P1-AS1 receives the data packet and pops the top label because it receives an implicit-null label mapping.
The resulting labeled packet (with VPN Label) is forwarded to PE1-AS1.
PE1-AS1 pops the VPN label and forwards the data packet to CE1-A.

MPLS L3VPN

MPLS L3VPN is a type of PE-based L3VPN technology for service provider VPN solutions.
It uses BGP to advertise VPN routes and uses MPLS to forward VPN packets on service provider backbones.
MPLS L3VPN provides flexible networking modes, excellent scalability, and convenient support for MPLS QoS and MPLS TE.

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Description

Learn about the main components of MPLS VPN architecture, including customer networks, CE routers, provider networks, and PE routers. Test your knowledge of this networking concept.