ADMINISTERING CISCO QoS IP NETWORKS - CHAPTER 12 pps

Multiprotocol Label Switching (MPLS) Solutions in this chapter: ■ Understanding MPLS ■ Integrating MPLS into QoS ■ Standardizing MPLS for Maximum Efficiency ■ Controlling MPLS Traffic Using Traffic Engineering ■ Integrating MPLS and Virtual Private Networking (VPN) Chapter 12 457 110_QoS_12 2/13/01 2:44 PM Page 457 458 Chapter 12 • Multiprotocol Label Switching (MPLS) Introduction Multiprotocol Label Switching is designed to forward packets through a network with extremely high performance by adding a label to packets as they enter the network at edge routers. Normally, every router along the packet’s path looks at each individual piece of the IP header. However, since MPLS applies a fairly simple label to each packet that includes all of the information needed to route the packet, the overhead created by each router looking through the packet’s header is greatly reduced, and the packet forwarding capabilities of each router are enhanced. This chapter, unlike earlier chapters, both introduces MPLS and shows some configuration examples. Since the basic theory of MPLS is fairly simple, separate chapters are not required to discuss theory and implementation. Relatively speaking, MPLS is a new technology, and there are many enhancements, such as the capability to use RSVP with MPLS to request labels, that are being devel- oped but are not yet fully deployable.This chapter focuses on the current RFCs pertaining to MPLS and does not discuss features that may not make it to full implementation. Understanding MPLS MPLS is the standardized version of Cisco Systems Tag Switching technology that integrates the flexibility and scalability of Layer 3 routing with the high perfor- mance and traffic-engineering capabilities of Layer 2 switching. MPLS is based on the concept of label swapping, in which packets or cells are assigned short, fixed- length labels that tell high-speed switching nodes how data should be forwarded. The key to understanding MPLS is to first identify the roles of each MPLS component.The main components are listed below, and you can see an illustra- tion of specific MPLS components in Figure 12.1. ■ Label A constant width identifier used to select how to forward a packet. Labels are also known as “Tags.”These labels are typically 32 bits in length unless MPLS is running over ATM.When MPLS is operating over an ATM infrastructure, the label size is an aggregate of the ATM VPI/VCI fields. ■ Edge Label Switch Routers or Label Edge Routers (LERs) Label edge routers are network layer routing devices located at the edges of a MPLS network.The primary function of the label edge routers is to apply labels, or tags, to packets entering the MPLS network, and remove labels from packets leaving the MPLS network. www.syngress.com 110_QoS_12 2/13/01 2:44 PM Page 458 www.syngress.com NOTE Label edge routers examine incoming packets from traditional routed environments and perform the appropriate security, accounting, and quality of service classifications. LERs run traditional routing protocols to determine network reachability information such as OSPF and IS-IS. Then, they apply the proper label to the packet and forward the packet to its next hop. ■ Label Switch Routers (LSR) Label switch routers are high-speed switching nodes whose main purpose is to forward packets at very high speeds. Label switch routers typically form the core of the network and run traditional IP routing protocols in order to gain knowledge of net- work layer reachability information.These devices are usually either high-speed routers or ATM switches. ■ Label Distribution Protocol (LDP) This protocol is used to dynam- ically distribute labels among MPLS network elements. Labels are con- sidered locally significant and must be unique on a per interface basis. Multiprotocol Label Switching (MPLS) • Chapter 12 459 Figure 12.1 MPLS Components Label Switch Routers Label Distribution Protocol (LDP) Label Edge Routers 110_QoS_12 2/13/01 2:44 PM Page 459 460 Chapter 12 • Multiprotocol Label Switching (MPLS) NOTE LDP uses UDP port 711 for neighbor discovery, and TCP port 711 to reli- ably exchange label information among MPLS devices. ■ Label Switched Path (LSP) This is a communications channel used to forward MPLS traffic between two MPLS enabled network elements. LSPs can be either dynamically created via label distribution protocol (LDP) or statically defined by the network administrator. ■ Label Information Base (LIB) This is the set of all labels learned from neighbor routers. LIB is populated via LDP. ■ Label Forwarding Information Base (LFIB) This is the set of labels that are actually used to forward packets. LFIB is derived from LIB. MPLS exercises a label-based forwarding mechanism in which labels are used to indicate both routes and service attributes.The ingress edge label switch router processes incoming packets and assigns a label to each packet.These packets are forwarded based on label toward the next hop router.The next hop routers simply read the labels and forward packets based on these labels.The key is to understand that processor-intensive analysis, classification, and filtering occur only once, at the ingress edge label switch router. Label switch routers in the core do not interrogate each packet; they merely switch each packet based solely on the assigned label. At the egress edge label switch router, labels are removed, and packets are forwarded to their final destination based on traditional routing methods. Label Switching Basics In a traditional router network, each router must process every packet to deter- mine the next hop that the packet must take to reach its final destination (see Figure 12.2).This action is repeated hop-by-hop, resulting in variable latencies through each router.This can adversely affect real-time applications that must maintain a low end-to-end delay. In contrast, in an MPLS network, only the label edge routers fully process each packet. Label switches within the network simply forward packets based on the label.This decreases the latency experienced by traditional routed networks performing standard IP routing.There are, of course, other reasons to deploy www.syngress.com 110_QoS_12 2/13/01 2:44 PM Page 460 Multiprotocol Label Switching (MPLS) • Chapter 12 461 MPLS, such as traffic engineering and VPNs.The other major difference between regular IP routing and label switching is the separation of the control and data planes–an essential concept for MPLS over ATM as well as TE. We can now proceed to discuss MPLS operation in more detail.The fol- lowing steps illustrate how packets are forwarded across an MPLS network. Refer to Figure 12.3 for illustrations of each step. 1. We begin with a group of routers running a traditional routing protocol such as OSPF or IS-IS.These routers are MPLS enabled and have estab- lished adjacencies with their neighbors. 2. After the routing tables have been populated, label distribution protocol dynamically binds labels to each IP route in the routing table, and by default advertises these label bindings to all neighbors. 3. As unlabeled IP packets enter the MPLS LER, the router queries its IP routing table and forwarding information base.The router determines which interface the packet should be forwarded through, and what label should be assigned to each packet.The decision of which interface to forward the packet through need not be made purely on the basis of destination prefix; therefore, an FEC (forwarding equivalence class) may represent a prefix but could also represent a type of packet or level of www.syngress.com Figure 12.2 Traditional IP Routing Illustration 0 1 1 100.89 172.69 0 100.89.25.4 Data 100.89 172.69 address prefix I/F 1 1 100.89 172.69 address prefix I/F 0 1 100.89 address prefix I/F 0 All Packets are forwarded based on their IP address 172.69 1 100.89.25.4 Data 100.89.25.4 Data 100.89.25.4 Data 110_QoS_12 2/13/01 2:44 PM Page 461 462 Chapter 12 • Multiprotocol Label Switching (MPLS) precedence.The router performs a label imposition to attach the label to the packet, and forwards the packet out the appropriate interface toward the next hop router. See Figure 12.4. www.syngress.com Figure 12.3 MPLS Conceptual Network Traditional Routing Protocol–OSPF; ISIS Label Distribution Protocol Labelled Packet Figure 12.4 MPLS Packet Flow 100.89 172.69 1 0 1 In Tag - - Address Prefix 100.89 100.89 172.69 Out I’face 1 1 Out Tag 7 5 In Tag 7 7 5 Address Prefix 100.89 172.69 Out I’face 0 1 Out Tag 8 7 100.89.25.4 Data 7 100.89.25.4 Data 100.89.25.4 Data 100.89.25.4 Data8 In Tag Address Prefix 100.89 Out I’face 0 Out Tag - 0 The LSR forwards packets based on label only Note: The term “tag” has been used instead of “label” to save sp 0 172.69 1 0 1 - - 100.89 7 8 - 0 0 110_QoS_12 2/13/01 2:44 PM Page 462 Multiprotocol Label Switching (MPLS) • Chapter 12 463 4. When a label switch router receives a labeled packet, the switch reads the label value of the incoming packet. Using the incoming label value as the index, the switch checks its label forwarding information base (FIB) to determine the outgoing label value and the outgoing interface. The incoming label value is replaced with the outgoing label value, and the packet is switched out the appropriate interface toward its next hop. 5. Packets are forwarded through the MPLS network in this manner hop by hop until they reach the egress label edge router.The label edge router performs a lookup of the incoming label in the forwarding infor- mation base and determines that there is no outgoing label.The router then strips off the label and forwards the packet as a traditional IP packet. That Sounds a Lot Like Routing! The separation of control and data planes allows additional Layer 3 routing ser- vices to be implemented without having to change the forwarding decision engine. Engineers who are used to configuring Cisco routers via IOS will feel comfortable configuring MPLS. Figure 12.5 illustrates a simple MPLS network. The configuration files are also provided for reference. The following is the output from the CORE LSR A Router. ! version 12.1 ! hostname Core-LSR-A www.syngress.com Figure 12.5 MPLS Network Example Configuration Core LSR A Loopback0=10.10.10.1/32 10.10.30.0/24 10.10.20.0/24 Edge LSR B Loopback0=10.10.10.2/32 Edge LSR C Loopback0=10.10.10.3/32 110_QoS_12 2/13/01 2:44 PM Page 463 464 Chapter 12 • Multiprotocol Label Switching (MPLS) ! ip subnet-zero ip cef ! interface Loopback0 ip address 10.10.10.1 255.255.255.255 no ip directed-broadcast ! interface Ethernet1/0 no ip address no ip directed-broadcast shutdown no cdp enable ! interface Ethernet1/1 no ip address no ip directed-broadcast shutdown no cdp enable ! interface Ethernet1/2 no ip address no ip directed-broadcast shutdown no cdp enable ! interface Ethernet1/3 no ip address no ip directed-broadcast shutdown no cdp enable ! interface FastEthernet2/0 IP unnumbered loopback0 www.syngress.com 110_QoS_12 2/13/01 2:44 PM Page 464 Multiprotocol Label Switching (MPLS) • Chapter 12 465 tag-switching ip ! interface FastEthernet2/1 IP unnumbered loopback0 tag-switching ip ! ! router ospf 10 network 10.0.0.0 0.255.255.255 area 0 ! ip classless no ip http server ! no cdp run ! line con 0 exec-timeout 0 0 transport input none line aux 0 line vty 0 4 password cisco no login ! end The following is the output of the EDGE LSR B Router. ! version 12.1 ! hostname Edge-LSR-B ! ip subnet-zero ip cef ! interface Loopback0 www.syngress.com 110_QoS_12 2/13/01 2:44 PM Page 465 466 Chapter 12 • Multiprotocol Label Switching (MPLS) ip address 10.10.10.2 255.255.255.255 ! interface Ethernet1/0 ip address 10.10.20.1 255.255.255.0 ! interface Ethernet1/1 no ip address no ip directed-broadcast shutdown no cdp enable ! interface Ethernet1/2 no ip address no ip directed-broadcast shutdown no cdp enable ! interface Ethernet1/3 no ip address no ip directed-broadcast shutdown no cdp enable ! interface FastEthernet2/0 IP unnumbered loopback0 tag-switching ip ! interface FastEthernet2/1 no ip address no ip directed-broadcast shutdown no cdp enable ! router ospf 10 network 10.0.0.0 0.255.255.255 area 0 www.syngress.com 110_QoS_12 2/13/01 2:44 PM Page 466 [...]... version 12. 1 ! www.syngress.com 10.10.50.0/24 110 _QoS_ 12 2/13/01 2:44 PM Page 483 Multiprotocol Label Switching (MPLS) • Chapter 12 hostname LSR-A ! ip subnet-zero ip cef ! interface Loopback0 ip address 10.10.10.1 255.255.255.255 no ip directed-broadcast ! interface Ethernet1/0 no ip address no ip directed-broadcast shutdown no cdp enable ! interface Ethernet1/1 no ip address no ip directed-broadcast... Ethernet1/2 no ip address no ip directed-broadcast shutdown no cdp enable ! interface Ethernet1/3 no ip address no ip directed-broadcast shutdown no cdp enable ! interface FastEthernet2/0 IP unnumbered loopback0 www.syngress.com 483 110 _QoS_ 12 484 2/13/01 2:44 PM Page 484 Chapter 12 • Multiprotocol Label Switching (MPLS) tag-switching ip ! interface FastEthernet2/1 IP unnumbered loopback0 tag-switching ip !... 10.10.10.3 send-community extended ! ip classless www.syngress.com 110 _QoS_ 12 2/13/01 2:44 PM Page 487 Multiprotocol Label Switching (MPLS) • Chapter 12 no ip http server ! no cdp run ! line con 0 exec-timeout 0 0 transport input none line aux 0 line vty 0 4 password cisco no login ! end The following is the configuration for PE LSR C ! version 12. 1 ! hostname Edge-LSR-C ! ip subnet-zero ip cef ! ip vrf RED... area 0 ! ip classless no ip http server ! no cdp run ! line con 0 exec-timeout 0 0 transport input none line aux 0 line vty 0 4 password cisco no login ! end The following is the configuration for PE LSR B ! version 12. 1 ! hostname LSR-B ! ip subnet-zero ip cef ! ip vrf RED www.syngress.com 110 _QoS_ 12 2/13/01 2:44 PM Page 485 Multiprotocol Label Switching (MPLS) • Chapter 12 rd 65050:1 route-target export...110 _QoS_ 12 2/13/01 2:44 PM Page 467 Multiprotocol Label Switching (MPLS) • Chapter 12 ! ip classless no ip http server ! no cdp run ! line con 0 exec-timeout 0 0 transport input none line aux 0 line vty 0 4 password cisco no login ! end The following output is from the EDGE LSR C Router ! version 12. 1 ! hostname Edge-LSR-C ! ip subnet-zero ip cef ! interface Loopback0 ip address 10.10.10.3... interface Ethernet1/0 ip address 10.10.30.1 255.255.255.0 ! interface Ethernet1/1 no ip address no ip directed-broadcast shutdown www.syngress.com 467 110 _QoS_ 12 468 2/13/01 2:44 PM Page 468 Chapter 12 • Multiprotocol Label Switching (MPLS) no cdp enable ! interface Ethernet1/2 no ip address no ip directed-broadcast shutdown no cdp enable ! interface Ethernet1/3 no ip address no ip directed-broadcast shutdown... redistribute bgp 65500 metric-type 1 subnets ! router bgp 65500 no synchronization no bgp default ipv4-unicast neighbor 10.10.10.3 remote-as 65500 neighbor 10.10.10.3 update-source loopback 0 ! address-family ipv4 vrf BLUE redistribute ospf 20 no autosummary exit-address-family ! address-family ipv4 vrf RED redistribute static redistribute static connected exit-address-family ! address-family vpnv4 neighbor... FastEthernet2/0 IP unnumbered loopback0 tag-switching ip ! interface FastEthernet2/1 no ip address no ip directed-broadcast shutdown no cdp enable ! router ospf 10 network 10.0.0.0 0.255.255.255 area 0 ! ip classless no ip http server ! no cdp run ! line con 0 exec-timeout 0 0 transport input none www.syngress.com 110 _QoS_ 12 2/13/01 2:44 PM Page 469 Multiprotocol Label Switching (MPLS) • Chapter 12 line aux... interface Ethernet1/1 no ip address no ip directed-broadcast shutdown no cdp enable ! interface Ethernet1/2 no ip address no ip directed-broadcast shutdown no cdp enable ! interface Ethernet1/3 no ip address no ip directed-broadcast shutdown no cdp enable ! interface FastEthernet2/0 IP unnumbered loopback0 tag-switching ip ! interface FastEthernet2/1 ip vrf forwarding BLUE ip address 10.10.70.1 255.255.255.0... www.syngress.com 110 _QoS_ 12 2/13/01 2:44 PM Page 489 Multiprotocol Label Switching (MPLS) • Chapter 12 network 10.0.0.0 0.255.255.255 area 0 redistribute bgp 65500 metric-type 1 subnets ! router bgp 65500 no synchronization no bgp default ipv4-unicast neighbor 10.10.10.2 remote-as 65500 neighbor 10.10.10.2 update-source loopback 0 ! address-family ipv4 vrf BLUE redistribute ospf 20 no autosummary exit-address-family . Router. ! version 12. 1 ! hostname Edge-LSR-B ! ip subnet-zero ip cef ! interface Loopback0 www.syngress.com 110 _QoS_ 12 2/13/01 2:44 PM Page 465 466 Chapter 12 • Multiprotocol Label Switching (MPLS) ip address. C Loopback0=10.10.10.3/32 110 _QoS_ 12 2/13/01 2:44 PM Page 463 464 Chapter 12 • Multiprotocol Label Switching (MPLS) ! ip subnet-zero ip cef ! interface Loopback0 ip address 10.10.10.1 255.255.255.255 no ip directed-broadcast ! interface. loopback0 www.syngress.com 110 _QoS_ 12 2/13/01 2:44 PM Page 464 Multiprotocol Label Switching (MPLS) • Chapter 12 465 tag-switching ip ! interface FastEthernet2/1 IP unnumbered loopback0 tag-switching ip ! ! router