Institute of Computer Technology - Vienna University of Technology. L85 - Multiprotocol Label Switching

Transcription

1 MPLS Multi-Protocol Label Switching Agenda Review Datagram- versus Virtual Call Service IP over WAN Problems (Traditional Approach) MPLS Principles Label Distribution Methods MPLS Details (Cisco) RFC s MPLS, v4.5 2 Page 85 -

2 Packet Switching Topology A T T2 B T2 T2 T4 T PED T3 Unique Network Address 3 T3 T4 of end system D PA T PD T2 6 T T 5 PB T2 PC C MPLS, v4.5 3 Routing Tables A A B destination B source D to next hop to B PS3 B C PS3 C to next hop D PS3 D B PS4 C PS5 D PS6 6 5 payload Routing Table of PS 4 next hop PS5 PS3 C MPLS, v4.5 4 Page 85-2

3 Datagram Service - Forwarding A B A C A B D B A B D B A B A C A B D B A C D D B 6 5 A C C MPLS, v4.5 5 Some Datagram Service Facts rerouting in case of topology changes means packets with the same information can take dferent paths to destination packets may be discarded by packet switches in case of network congestion or transmission errors best effort service transport of packets depends on available resources the end systems are responsible for error recovery connectionless behavior reservation of resources is not possible in an easy way bandwidth on trunk line buffer memory (delay!) of packet switches MPLS, v4.5 6 Page 85-3

4 Virtual Call Setup connection identier packet type A B 4 CR A B unique es Switching Table of PS 4 to B C E next hop PS3 PS3 PS3 from A :4 to from to from to E 6 C 5 CR Call Request IC Incoming Call MPLS, v4.5 7 Virtual Call Setup 2 A B from to from to from to 23 CR A B A :4 3:23 2 :23 to next hop E 6 CR Call Request B PS4 C PS5 E PS6 C 5 IC Incoming Call MPLS, v4.5 8 Page 85-4

5 Virtual Call Setup 3 A B 4 from to :7 from to A :4 3:23 from to 7 CR A B to B C E next hop PS5 PS3 2 :23 4:7 E 6 C 5 CR Call Request IC Incoming Call MPLS, v4.5 9 Virtual Call Setup 4 A Virtual connection A - B: B 4 44 IC A B from to 23 from to A :4 3:23 3:7 B:44 from to 2 :23 4:7 E 6 C 5 CR Call Request IC Incoming Call MPLS, v4.5 Page 85-5

6 Data Transfer A Virtual connection A - B: B D from to 23 from to A :4 3:23 3:7 B:44 from to 2 :23 4:7 E 6 C 5 D Data Packet payload MPLS, v4.5 Data Transfer 2 A Virtual connection A - B: B 4 44 D from to 23 from to A :4 3:23 3:7 B:44 from to 2 :23 4:7 E 6 C 5 D Data Packet payload MPLS, v4.5 2 Page 85-6

7 Data Transfer 3 A Virtual connection A - B: B from to A :4 3:23 23 D 7 from to 3:7 B:44 from to 2 :23 4:7 E 6 C 5 D Data Packet payload MPLS, v4.5 3 Data Transfer 4 A Virtual connection A - B: B 4 44 D from to 23 from to A :4 3:23 3:7 B:44 from to 2 :23 4:7 E 6 C 5 D Data Packet payload MPLS, v4.5 4 Page 85-7

8 Example Virtual Circuits A 4 virtual circuit A-B ( ) 44 B virtual circuit A-C ( ) 7 E 44 C MPLS, v4.5 5 Some Virtual Call Service Facts connection-oriented packet switching allows reservation of resources capacity, buffers, cpu time, etc. can offer Quality of Service (QoS) call setup can be denied by network QoS can not be guaranteed the sequence of data packets is guaranteed by the network packets can use the established path only path selection is done during connection setup afterwards, entries of routing table are not used in case of trunk line or packet switch failure virtual circuits will be closed and must be reestablished again by end systems using call setup packets MPLS, v4.5 6 Page 85-8

9 Network Technologies based on Virtual Call Method X.25 reliable transport pipe because of protocol inherent error recovery and flow control identier = LCN; in-band signaling Frame Relay virtual circuit technique but no error recovery congestion indication instead of flow control identier = DLCI; out-band signaling ATM same as Frame Relay but packets with fixed length hence called cell switching identier = VPI/VCI; out-band signaling MPLS, v4.5 7 ATM Scenario -> VPI / VCI A VPI/VCI = /5 (A->B) ATM-DTE ATM-DCE ATM-DCE VPI/VCI = /44 2 ATM-DTE B 3 4 VPI/VCI = /99 C D VPI/VCI = /88 (D->C) ATM-DTE ATM-DTE MPLS, v4.5 8 Page 85-9

10 ATM Switching Tables ATM-DTE ATM-DCE ATM-DTE A B from I from I: /77 O2: /99 I4: /77 O3: 4/88 2 to I: /5 O3: /77 O3 I I4 to O2 O3 I4 O2 from Switching Table of ATM Switch 2 to I4: /99 O2: /44 D I O2 I O3 3 from to from to I: /88 O2: /77 I: 4/88 O3: 2/99 MPLS, v C Cell Forwarding / Label Swapping Cell Header (5 Byte) Payload (48 byte) A B 5 I VPI / VCI O3 from to I: /5 O3: /77 from to I: /77 O2: /99 I4: /77 O3: 4/88 I I4 O2 O3 I4 O2 from to I4: /99 O2: /44 88 I O2 I O3 from to D from to I: /88 O2: /77 C I: 4/88 O3: 2/99 MPLS, v4.5 2 Page 85 -

11 Cell Forwarding / Label Swapping 2 A B I from to I: /77 O2: /99 I4: /77 O3: 4/88 2 O3 from to I: /5 O3: /77 D O2 I4 from to 77 I O3 I4: /99 O2: /44 I4 77 O2 I I O3 3 from to from to I: /88 O2: /77 I: 4/88 O3: 2/99 MPLS, v O2 C Cell Forwarding / Label Swapping 3 A B I from to I: /77 O2: /99 I4: /77 O3: 4/88 2 O3 O2 I4 from to from to I O3 99 I4: /99 O2: /44 I: /5 O3: /77 I4 O2 D I O I O3 3 from to from to I: /88 O2: /77 I: 4/88 O3: 2/99 MPLS, v C Page 85 -

12 Cell Forwarding / Label Swapping 4 A B 44 I from to O2 I: /77 O2: /99 I4: /77 O3: 4/88 2 O3 O2 I4 from to from to I O3 I4: /99 O2: /44 I: /5 O3: /77 I4 D I O2 I 2 99 O3 3 from to from to I: /88 O2: /77 I: 4/88 O3: 2/99 MPLS, v C Segmentation Principle Cells are much smaller than data packets Segmentation and Reassembly is necessary in ATM DTE s (!!!) ATM DCE s (ATM switches) are not involved in that H Datagram SDU BOM COM COM COM COM EOM PAD H 44 Octet T 5 48 H Payload H Payload H Payload H 44 Octet T T Bitstream MPLS, v Page 85-2

13 ATM Routing in Private ATM Networks PNNI is based on Link-State technique like OSPF Topology database Every switch maintains a database representing the states of the links and the switches Extension to link state routing!!! Announce status of node (!) as well as status of links Contains dynamic parameters like delay, available cell rate, etc. versus static-only parameters of OSPF (link up/down, node up/down, nominal bandwidth of link) Path determination based on metrics Much more complex than with standard routing protocols because of ATM-inherent QoS support MPLS, v PNNI Routing Generic Connection Admission Control (GCAC) Used by the source switch to select a path through the network Calculates the expected CAC (Connection Admission Control) behavior of another node. Support this QoS ly? CAC UNI/NNI 2. Yes/No GCAC 3.) Is it likely that path will deliver expected QoS? MPLS, v Page 85-3

14 PNNI Routing (Simple QoS -> ACR only) Operation of the GCAC CR Cell Rate ACR Available Cell Rate D Distance like OSPF costs ATM-DCE ATM-DTE S2 ACR = 2 S6 Requested CR = 3 ATM-DTE S ATM-DCE ACR = ACR = 5, D = 5 ACR = 5 D = 5 S3 ACR = 4 D = 5 ACR = 5 D = ACR = 5 D = 5 S4 S5 ACR = 4 D = 5 MPLS, v PNNI Routing Operation of the GCAC ) Links not supporting requested CR are eliminated -> Metric component -> ACR value used Requested CR = 3 S2 ACR = 2 S6 S ACR = ACR = 5, D = 5 ACR = 5 D = 5 S3 ACR = 4 D = 5 ACR = 5 D = ACR = 5 D = 5 S4 S5 ACR = 4 D = 5 MPLS, v Page 85-4

15 PNNI Routing Operation of the GCAC 2) Next, shortest path(s) to the destination is (are) calculated Metric component -> Distance value used Requested CR = 3 S2 ACR = 2 S6 S ACR = ACR = 5, D = 5 ACR = 5 D = 5 S3 ACR = 4 D = 5 ACR = 5 D = ACR = 5 D = 5 S4 S5 ACR = 4 D = 5 MPLS, v PNNI Routing Operation of the GCAC 3) One path is chosen and source node S constructs a Designated Transit List (DTL) -> source routing --> Describes the complete route to the destination Requested CR = 3 S2 ACR = 2 S6 S ACR = ACR = 5, D = 5 ACR = 5 D = 5 S3 ACR = 4 D = 5 ACR = 5 D = ACR = 5 D = 5 S4 MPLS, v4.5 3 S5 ACR = 4 D = 5 requested ACR = 3 Page 85-5

16 PNNI Routing - Source Routing Operation of the GCAC 4) DTL is inserted into signaling request and moved on to next switch 5) After receipt next switch perform CAC 5a) ok -> pass PNNI signaling message on to next switch of DTL 6a) finally signaling request will reach destination ATM-DTE -> VC ok PNNI Signaling with DTL list S2 ACR = 2 S6 S ACR = ACR = 5, D = 5 ACR = 5 D = 5 S3 ACR = 4 D = 5 ACR = 5 D = ACR = 5 D = 5 S4 S5 ACR = 4 D = 5 requested ACR = 3 MPLS, v4.5 3 PNNI Routing - Crankbank Operation of the GCAC 5) After receipt next switch (S2) perform CAC 5b) nok -> return PNNI signaling message to originator of DTL 6b) S will construct alternate source route PNNI Signaling with DTL list S2 cannot fulfill requirements on trunk to S5 S2 ACR = 2 S6 S ACR = ACR = 5 D = 5 S3 ACR = 4 D = 5 ACR = 5, D = 5 ACR = 5 D = ACR = 5 D = 5 Crankbank to S S4 S5 ACR = 4 D = 5 requested ACR = 3 MPLS, v Page 85-6

17 PNNI Routing - New Trial Operation after Crankbank 7b) The other possible path is chosen - source node constructs again a new Designated Transit List (DTL) Requested CR = 3 S2 ACR = 2 S6 S ACR = ACR = 5, D = 5 ACR = 5 D = 5 S3 ACR = 4 D = 5 ACR = 5 D = ACR = 5 D = 5 S4 MPLS, v S5 ACR = 4 D = 5 requested ACR = 3 PNNI Routing - Source Routing Operation of the GCAC 8b) DTL is inserted into signaling request 9b) After receipt next switch perform CAC ok -> pass PNNI signaling message on to next switch of DTL b) finally signaling request will reach destination ATM-DTE -> VC ok PNNI Signaling with DTL list S2 ACR = 2 S6 S ACR = ACR = 5, D = 5 ACR = 5 D = 5 S3 ACR = 4 D = 5 ACR = 5 D = ACR = 5 D = 5 S4 S5 ACR = 4 D = 5 requested ACR = 3 MPLS, v Page 85-7

18 Agenda Review Datagram- versus Virtual Call Service IP over WAN Problems (Traditional Approach) MPLS Principles Label Distribution Methods MPLS Details (Cisco) RFC s MPLS, v IP Overlay Model - Scalability Base problem Nr. IP routing separated from ATM routing because of the normal IP overlay model no exchange of routing information between IP and ATM world leads to scalability and performance problems many peers, configuration overhead, duplicate broadcasts note: IP system requests virtual circuits from the ATM network ATM virtual circuits are established according to PNNI routing virtual circuits are treated by IP as normal point-to-point links IP routing messages are transported via this point-to-point links to discover IP neighbors and IP network topology MPLS, v Page 85-8

19 A Simple Physical Network Physical wiring MPLS, v IP Data Link View (Non-NBMA) Every virtual circuit has its own IP Net-ID (subinterface technique) MPLS, v Page 85-9

20 A Single Network Failure MPLS, v Causes Loss of Multiple IP Router Peers!!! MPLS, v4.5 4 Page 85-2

21 Example - Physical Topology net A net B net A-A net B-B Ra Rb net D-D Sa Sb net C-C net D Rd Sd Sc Rc net C MPLS, v4.5 4 IP Connectivity through Full-mesh VC s net A net B net A-A net B-B Ra Rb net D-D net C-C net D Rd Rc net C MPLS, v Page 85-2

22 Static Routing/No Routing Broadcasts net A-A net A net B net B-B Ra Rb net D-D net C-C net D Rd Configuration Router Rd static routing resolution PVC resolution SVC net A via next hopra Ra map VPI/VCI Rd Ra Ra map ATM addr. Ra net B via next hoprb Rb map VPI/VCI Rd Rb Rb map ATM addr. Rb net C via next hoprc Rc map VPI/VCI Rd Rc Rc map ATM addr. Rc every remote network listed here! Rc net C MPLS, v Dynamic Routing/Routing Broadcasts net A-A net A net B net B-B Ra Rb net D-D net C-C Configuration Router Rd net D Rd Rc dynamic routing on PVC resolution PVC net C VPI/VCI Rd Ra broadcast Ra map VPI/VCI Rd Ra VPI/VCI Rd Rb broadcast Rb map VPI/VCI Rd Rb VPI/VCI Rd Rc broadcast Rc map VPI/VCI Rd Rc note: SVCs may be possible Cisco neighbor command is specied for Cisco routing process because no automatic neighbor discovery is possible in this case MPLS, v Page 85-22

23 Observations This clearly does not scale Switch/router interaction needed peering model Without MPLS Only outside routers are layer 3 neighbors one ATM link failure causes multiple peer failures routing traffic does not scale (number of peers) With MPLS Inside MPLS switch is the layer 3 routing peer of an outside router one ATM link failure causes one peer failure highly improved routing traffic scalability MPLS, v A Simple Physical Network Physical wiring and NBMA behavior MPLS, v Page 85-23

24 IP Data Link View (NBMA) Routers assume a LAN behavior because all interfaces have the same IP Net-ID but LAN broadcasting to reach all others is not possible LIS Logical IP Subnet MPLS, v Some Solutions for the NBMA Problem ARP (Address Resolution Protocol) Server keeps configuration overhead for resolution small but does not solve the routing issue (neighbor discovery and duplicate routing broadcasts on a single wire) MARS/MCS (Multicast Address Resolution Server / Multicast Server) additional keeps configuration overhead for routing small and does solve broadcast/multicast problem with either full mesh of point-to-multipoint circuits or by usage of MCS server LANE (LAN Emulation = ATM VLAN s) simulates LAN behavior where resolution and routing broadcasts are not a problem All of them require a lot of control virtual circuits (p-t-p and p-t-m) and SVC support of the underlying ATM network MPLS, v Page 85-24

25 RFC 2225 Operation (Classical IP over ATM) ARP server for every LIS multiple hops for communication between Logical IP Subnets ARP Server Subnet ATM Network LIS LIS2 ARP Server Subnet 2 MPLS, v MARS/MCS Architecture Control VC MARS MCS CLIENT Server Control VC Cluster Control VC CLIENT CLIENT MCS point-to-multipoint data VC CLIENT CLIENT CLIENT MPLS, v4.5 5 Page 85-25

26 LANE Connections LES Control Direct Control Direct Control Distribute Data Direct (SVC -> VC on Demand) Multicast Forward Configure Direct Multicast Send LECS MPLS, v4.5 5 BUS Scalability Aspects Number of IP peers determines number of data virtual circuits number of control virtual circuits number of duplicate broadcasts on a single wire Method to solve the broadcast domain problem split the network in several LIS (logical IP subnets) connect LIS s by normal IP router (ATM-DCE) which is of course outside the ATM network But then another problem arise traffic between to two systems which both are attached to the ATM network but belong to dferent LIS s must leave the ATM network and enter it again at the connecting IP router (-> SAR delay) MPLS, v Page 85-26

27 IP Multiple LIS s in case of ROLC (Routing Over Large Clouds) IP router A connects LIS and LIS2 Router A LIS LIS 2 MPLS, v Some Solutions for the ROLC Problem NHRP (Next Hop Resolution Protocol) creates an ATM shortcut between two systems of dferent LIS s MPOA (Multi Protocol Over ATM) LANE + NHRP combined creates an ATM shortcut between two systems of dferent LIS s In both methods the ATM shortcut is created traffic between the two systems exceeds a certain threshold -> data-flow driven a lot of control virtual circuits (p-t-p and p-t-m) is required MPLS, v Page 85-27

28 Wish for Optimized Connectivity Logical Network LIS2 Source Logical Network LIS ATM Network Logical Network LIS4 Logical Network LIS3 Classical Path Optimized Path Destination MPLS, v Next Hop Resolution Protocol (RFC 2332) NHS2 NHS3 NH-Request NH-Reply NHS NHS4 Next Hop Server ATM Network LIS LIS2 LIS3 LIS4 Direct Connection Next hop requests are passed between next hop servers Next hop servers do not forward data NHS that knows about the destination sends back a NH-reply Allows direct connection between logical IP subnets across the ATM cloud Separates data forwarding path from reachability information MPLS, v Page 85-28

29 IP Performance Base problem Nr.2 IP forwarding is slow compared to ATM cell forwarding IP routing paradigm hop-by-hop routing with (recursive) IP routing table lookup, IP TTL decrement and IP checksum computing destination based routing (large tables in the core of the Internet) Load balancing in a stable network all IP datagram's will follow the same path (least cost routing versus ATM s QoS routing) QoS (Quality of Service) IP is connectionless packet switching (best-effort delivery versus ATM s guarantees) VPN (Virtual Private Networks) ATM VC s have a natural closed user group (=VPN) behavior MPLS, v Basic Ideas to Solve the Problems Make ATM topology visible to IP routing to solve the scalability problems a classical ATM switch gets IP router functionality Divide IP routing from IP forwarding to solve the performance problems IP forwarding based on ATM s swapping paradigm (connection-oriented packet switching) IP routing based on classical IP routing protocols Combine best of both forwarding based on ATM swapping paradigm routing done by traditional IP routing protocols MPLS, v Page 85-29

30 MPLS Several similar technologies were invented in the mid-99s IP Switching (Ipsilon) Cell Switching Router (CSR, Toshiba) Tag Switching (Cisco) Aggregated Route-Based IP Switching (ARIS, IBM) IETF merges these technologies MPLS (Multi Protocol Label Switching) note: multiprotocol means that IP is just one possible protocol to be transported by a MPLS switched network RFC 33 MPLS, v MPLS Building Blocks MPLS VPN (Virtual Private Network) MPLS Multicast MPLS Transport MPLS ATOM (Any Transport over MPLS) MPLS TE (Traffic Engineering) MPLS QoS (Quality of Service) You always need this! MPLS Transport solves most of the mentioned problems (scalability / performance) If you need "Advanced Features like VPN or Multicast support you optionally may choose from these building blocks riding on top of a MPLS Transport network MPLS, v4.5 6 Page 85-3

31 Agenda Review Datagram- versus Virtual Call Service IP over WAN Problems (Traditional Approach) MPLS Principles Label Distribution Methods MPLS Details (Cisco) RFC s MPLS, v4.5 6 MPLS Approach Traditional IP uses the same information for path determination (routing) packet forwarding (switching) MPLS separates the tasks L3 es used for path determination s used for switching MPLS Network consists of MPLS Edge Routers and MPLS Switches Edge Routers and Switches exchange routing information about L3 IP networks exchange forwarding information about the actual usage of s MPLS, v Page 85-3

32 MPLS Network MPLS Edge Router or LER (Label Edge Router) MPLS Switch or LSR (Label Switching Router) MPLS Network Router Component + Control Component Forwarding Component MPLS, v MPLS LSR Internal Components Routing Component still accomplished by using standard IP routing protocols creating routing table Control Component maintains correct distribution among a group of switches Label Distribution Protocol for communication between MPLS Switches between MPLS Switch and MPLS Edge Router Forwarding Component uses s carried by packets plus information maintained by a switch (classical VC switching table) to perform packet forwarding -> swapping MPLS, v Page 85-32

33 MPLS Control Communication Label Distribution Protocol Routing Protocol MPLS, v Generic Overview of MPLS LSR Internal Processes and Communication Routing Protocol Label Distribution Protocol control packets in for routing and distribution Routing Table () Routing Component Control Component Label Mgt. Process Routing Process Label Information Base (LIB) Routing Protocol Label Distribution Protocol control packets out for routing and distribution ed data packets in Forwarding Component Forwarding Process Label Switching Table ed data packets out MPLS, v Page 85-33

34 MPLS Basic Operations a. Routing protocol (e.g. OSPF) establishes reachability to destination networks b. Label Distribution Protocol establishes MPLS paths (VC) along switching tables 4. Egress MPLS router at egress removes and delivers packet 2. Ingress MPLS router receives packet, s it and by sends it along a particular MPLS path (VC) 3. MPLS switches ed packets using switching table MPLS, v MPLS Header: Frame Mode One 4 Byte MPLS header Layer 2 (Ethernet, PPP) Label Exp S TTL IP 2 Bit 3 8 Label Stack Layer 2 MPLS Header MPLS Header 2 MPLS Header 3 IP "Layer 2.5 can be used over Ethernet, 82.3 or PPP links note: 2.5 means 32 bit 2-bit MPLS (Label) 3-bit experimental field (Exp) could be copy of IP Precedence -> MPLS QoS like IP QoS with DfServ Model based on DSCP -bit bottom-of-stack indicator (S) Labels could be stacked (Push & Pop) MPLS switching performed always on the first of the stack 8-bit time-to-live field (TTL) MPLS, v Page 85-34

35 MPLS Header: Cell Mode MPLS Header MPLS Header 2 IP Packet ATM Convergence Sublayer (CS): MPLS Header MPLS Header 2 IP Packet AAL5 Trailer ATM Switches can only switch VPI/VCI no MPLS s! Only the topmost is inserted in the VPI/VCI field ATM Segmentation and Reassembling Sublayer (SAR): (first cell) GFC VPI VCI PTI CLP HEC MPLS Header(s) IP Header DATA Topmost Label (subsequent cells) GFC VPI VCI PTI CLP HEC DATA Topmost Label MPLS, v Labels and FEC A is used to identy a certain subset of packets which take the same MPLS path or which get the same forwarding treatment in the MPLS switched network The path is so called Label Switched Path (LSP) The MPLS Virtual Circuit Thus a represents a so called Forwarding Equivalence Class (FEC) The assignment of a packet to FEC is done just once by the MPLS Edge Router, as the packet enters the network most commonly this is based on the IP network layer destination MPLS, v4.5 7 Page 85-35

36 Label Binding Two neighboring LSR s R and R2 may agree that when R transmits a packet to R2, R will with packet with value L and only the packet is a member of a particular FEC F They agree on a so called "binding" between L and FEC F for packets moving from R to R2 As a result L becomes R s "outgoing " or remote representing FEC F L becomes R2 s "incoming " or representing FEC F MPLS, v4.5 7 Creating and Destroying Label Binding Control Driven (favored by IETF-WG) creation or deconstruction of s is triggered by control information such as OSPF routing, IS-IS routing PIM Join/Prune messages in case of IP multicast routing IntSrv RSVP messages in case of IP QoS IntSrv Model DfSrv Traffic Engineering in Case of IP QoS DfSrv Model hence we have a pre-assignment of s based on reachability information and optionally based on QoS needs also called Topology Driven MPLS, v Page 85-36

37 Creating and Destroying Label Binding 2 Data Driven creation or deconstruction of s is triggered by data packets but only a critical threshold number of packets for a specic communication relationship is reached may have a big performance impact hence we have dynamic assignment of s based on data flow detection also called Traffic Driven MPLS, v Some FEC Examples for Topology Driven FEC s could be for example a set of unicast packets whose network layer destination matches a particular IP MPLS application: Destination Based (Unicast) Routing a set of multicast packets with the same source and destination network layer MPLS application: Multicast Routing a set of unicast packets whose network layer destination matches a particular IP and whose Type of Service (ToS) or DSCP bits are the same MPLS application: Quality of Service MPLS application: Traffic Engineering or Constraint Based Routing MPLS, v Page 85-37

38 Label Distribution MPLS architecture allows an LSR to distribute bindings to LSR s that have not explicitly requested them Unsolicited Downstream" distribution usually used by Frame-Mode MPLS MPLS architecture allows an LSR to explicitly request, from its next hop for a particular FEC, a binding for that FEC Downstream-On-Demand" distribution must be used by Cell-Mode MPLS MPLS, v Label Binding The decision to bind a particular L to a particular FEC F is made by the LSR which is DOWNSTREAM with respect to that binding the downstream LSR then informs the upstream LSR of the binding thus s are "downstream-assigned thus bindings are distributed in the "downstream to upstream direction Discussion were about s should also be upstream-assigned not any longer part of current MPLS-RFC MPLS, v Page 85-38

39 Label Retention Mode A LSR may receive a binding for a particular FEC from another LSR, which is not next hop based on the routing table for that FEC This LSR then has the choice of whether to keep track of such bindings, or whether to discard such bindings A LSR supports "Liberal Label Retention Mode" it maintains the bindings between a and a FEC which are received from LSR s which are not its next hop for that FEC MPLS, v Label Retention Mode 2 A LSR supports "Conservative Label Retention mode " If it discards the bindings between a and a FEC which are received from LSR s which are not its next hop for that FEC Liberal Label Retention mode allows for quicker adaptation to routing changes LSR can switch over to next best LSP Conservative Label Retention mode requires an LSR to maintain fewer s LSR has to wait for new bindings in case of topology changes MPLS, v Page 85-39

40 Independent versus Ordered Control Independent Control: each LSR may make an independent decision to assign a a to a FEC and to advertise the assignment to its neighbors typically used in Frame-Mode MPLS for destination based routing loop prevention must be done by other means (-> MPLS TTL) but there is faster convergence Ordered Control: assignment proceeds in an orderly fashion from one end of a LSP to the other under ordered control, LSP setup may be initiated by the ingress (header) or egress (tail) MPLS Edge Router MPLS, v Ordered Control - Egress in case of egress method the only LSR which can initiate the process of assignment is the egress LSR a LSR knows that it is the egress for a given FEC its next hop for this FEC is not an LSR this LSR will sent a advertisement to all neighboring LSR s a neighboring LSR receiving such a advertisement from a interface which is the next hop to a given FEC will assign its own and advertise it to all other neighboring LSR s inherent loop prevention slower convergence MPLS, v4.5 8 Page 85-4

41 Ordered Control - Ingress in case of ingress method the LSR which initiates the process of assignment is the ingress LSR the ingress LSR constructs a source route and pass on requests for bindings to the next LSR this is done until LSR which is the end of the source route is reached from this LSR bindings will flow upstream to the ingress LSR used for MPLS Traffic Engineering (TE) MPLS, v4.5 8 MPLS Applications and MPLS Control Plane Dferent Control Planes Unicast Fwd. Multicast Fwd. MPLS TE MPLS QoS MPLS VPN Any IGP OSPF/ISIS Any IGP Any IGP IP M- IP IP IP LDP/TDP PIMv2 LDP RSVP LDP/TDP LDP BGP Data Plane (Forwarding Plane) Label Switching Table MPLS, v Page 85-4

42 Agenda Review Datagram- versus Virtual Call Service IP over WAN Problems (Traditional Approach) MPLS Principles Label Distribution Methods Unsolicited Downstream Downstream On Demand MPLS and ATM, VC Merge Problem MPLS Details (Cisco) RFC s MPLS, v Routing Table Created by Routing Protocol FEC Label Binding: Control Driven Destination Based Routing i/f interface i/f interface LSR Routing Table interface LER LER i/f LER i/f i/f 7.69 Data Flow interface 7.69 MPLS, v Page 85-42

43 Labels Sent by LDP x x Label Distribution: Unsolicited Downstream remote i/f remote i/f Switching Table (ST) remote 5 x Advertises binding <5,28.89.> Routing Table () Label Binding i/f Advertisings received from the IP next hop () for those networks (FEC s) -> switching table i/f Advertises binding <7,7.69> i/f 7.69 Data Flow 7 remote x 7.69 MPLS, v Labels Sent and Switching Table Entry Created by MPLS Switch x x Label Distribution: Unsolicited Downstream remote remote Label Binding i/f 5 remote x i/f i/f Advertises bindings <3,28.89.> <4,7.69> i/f Advertisings received from the IP next hop () for those networks (FEC s) -> switching table Data Flow 7 remote x i/f MPLS, v Page 85-43

44 MPLS Switched Packets x x remote remote MPLS Path = LSP to FEC Label Swapping MPLS Path = LSP to FEC data data MPLS Edge Router does longest match, adds ( impose ) Data Flow subsequent MPLS switch forwards on (based on ST), swaps data last MPLS router strip off the ( untag ) and routes packet based on data remote x 7.69 MPLS, v Routing Table Created by Routing Protocol FEC Label Binding: Control Driven Destination Based Routing interface interface interface i/f LER i/f i/f LSR LER LER i/f Data Flow interface MPLS, v Page 85-44

45 Labels Sent by LDP 5 Label Distribution: Unsolicited Downstream remote x remote x remote i/f i/f i/f Advertises binding <5, > i/f Advertising received from the IP next hop () for those networks (FEC s) -> switching table x Data Flow remote MPLS, v Labels Sent and Switching Table Entry Created by MPLS Switch remote x i/f Label Distribution: Unsolicited Downstream Data Flow remote 7 5 i/f remote x 7 remote x MPLS, v4.5 9 Advertises binding <7, > i/f Advertisings received from the IP next hop () for those networks (FEC s) -> switching table Advertises binding <7, > i/f Page 85-45

46 Label Merging - LSP Merging 5 remote x remote x remote MPLS Path = LSP to FEC MPLS Path = LPS to FEC MPLS Path = LSP to FEC data data last MPLS router strip off the and routes packet Data Flow subsequent 7 MPLS switch forwards on, swaps data data MPLS Edge Router does longest match, adds ( imose ) MPLS, v4.5 9 Agenda Review Datagram- versus Virtual Call Service IP over WAN Problems (Traditional Approach) MPLS Principles Label Distribution Methods Unsolicited Downstream Downstream On Demand MPLS and ATM, VC Merge Problem MPLS Details (Cisco) RFC s MPLS, v Page 85-46

47 Routing Table Created by Routing Protocol FEC Label Binding: Control Driven Destination Based Routing i/f interface i/f interface LSR interface LER LER i/f LER i/f i/f 7.69 interface 7.69 MPLS, v Labels Requested by MPLS Edge Routers x x Label Distribution: Downstream-On-Demand remote remote i/f remote x i/f i/f Data Flow Request binding <28.89.> i/f Request binding <7.69> Request binding are sent in direction of the IP next hop () for these networks (FEC s) remote x i/f MPLS, v Page 85-47

48 Labels Requested by MPLS Switch x x Label Distribution: Downstream-On-Demand remote i/f remote i/f i/f Request binding <28.89.> Request binding <7.69> remote x i/f i/f Request binding are passed on in direction of the IP next hop () for these networks (FEC s) 7.69 Data Flow remote x 7.69 MPLS, v Labels Allocated by MPLS Edge Router x x Label Distribution: Downstream-On-Demand remote i/f remote i/f remote 5 x i/f Advertises binding <5,28.89.> Advertise-Bindings caused by former requests will lead to entries in the switching table i/f Advertises binding <7,7.69> i/f 7.69 Data Flow 7 remote x 7.69 MPLS, v Page 85-48

49 Labels Allocated and Switching Table Built by MPLS Switch x x Label Distribution: Downstream-On-Demand remote remote i/f 5 remote x i/f i/f Advertises bindings <3,28.89.> <4,7.69> i/f i/f 7.69 Data Flow Advertise-Bindings caused by former requests will lead to entries in the switching table 7 remote x 7.69 MPLS, v MPLS Switched Packets x x remote remote MPLS Path = LSP to FEC data data MPLS Edge Router does longest match, adds Data Flow subsequent MPLS switch forwards solely on, swaps data 7 remote x MPLS Path = LSP to FEC 7.69 last MPLS router strip off the and routes packet data MPLS, v Page 85-49

50 Routing Table Created by Routing Protocol FEC Label Binding: Control Driven Destination Based Routing interface interface interface i/f LER i/f i/f LSR LER LER i/f Data Flow interface MPLS, v Labels Requested by MPLS Edge Routers Label Distribution: Downstream-On-Demand remote x in- 2 remote i/f out- i/f requests binding < > remote x i/f i/f request binding < > i/f 2 i/f Data Flow remote x MPLS, v4.5 Page 85-5

51 Labels Requested by MPLS Switch Label Distribution: Downstream-On-Demand remote x in- 2 remote i/f out- i/f remote x i/f i/f requests binding < > i/f 2 i/f Data Flow request binding < > remote x MPLS, v4.5 Labels Allocated by MPLS Edge Router 5 7 Label Distribution: Downstream-On-Demand remote x x in- 2 remote i/f out- i/f remote x i/f i/f advertise binding < 5, > i/f 2 i/f advertise binding <7, > Data Flow remote x MPLS, v4.5 2 Page 85-5

52 Labels Allocated and Switching Table Built by MPLS Switch 5 7 Label Distribution: Downstream-On-Demand remote x x in- remote i/f out- advertise binding <3, > 3 i/f remote x i/f i/f i/f 2 advertise binding <4, > i/f Data Flow 4 remote x MPLS, v4.5 3 Two Separate LSP s remote x x MPLS Path = LPS to FEC in- remote out- MPLS Path = LSP to FEC remote 3 x 4 remote x MPLS Path 2 = LSP 2 to FEC data data 2 last MPLS router strip off the and routes packet Data Flow subsequent MPLS switch forwards solely on, swaps data data MPLS Edge Router does longest match, adds MPLS, v4.5 4 Page 85-52

53 Agenda Review Datagram- versus Virtual Call Service IP over WAN Problems (Traditional Approach) MPLS Principles Label Distribution Methods Unsolicited Downstream Downstream On Demand MPLS and ATM, VC Merge Problem MPLS Details (Cisco) RFC s MPLS, v4.5 5 Label Switching and ATM Can be easily deployed with ATM because ATM uses swapping VPI/VCI is used as a ATM switches needs to implement control component of switching ATM attached router peers with ATM switch ( switch) exchange binding information Dferences how s are set up distribution -> downstream on demand allocation merging in order to scale, merging of multiple streams (s) into one stream () is required MPLS, v4.5 6 Page 85-53

54 Label Switching and ATM IP Packet 5 remote 3 y IP Packet ATM switch interleaves cells of dferent packets onto same. That is a problem in case of AAL5 encapsulation. No problem in case of AAL3/AAL4 encapsulation because of AAL3/AAL4 s inherent multiplexing capability. MPLS, v4.5 7 Label Distribution Solution for ATM requests a for input i/f remote output i/f requests a for requests two s for returns a to each requester Downstream On Demand Label Distribution MPLS, v4.5 8 Page 85-54

55 Label Distribution Solution for ATM input i/f remote output i/f Downstream On Demand distribution is necessary multiple s per FEC may be assigned one per (ingress, egress) router pair Label space can be reduced with VC-merge technique MPLS, v4.5 9 VC Merge Technique 5 remote ATM switch avoids interleaving of frames VC Merge technique looking for AAL5 trailers and storing corresponding cells of a frame until AAL5 trailer is seen MPLS, v4.5 Page 85-55

56 Agenda Review Datagram- versus Virtual Call Service IP over WAN Problems (Traditional Approach) MPLS Principles Label Distribution Methods MPLS Details (Cisco) Internal Components MPLS in Action TDP, LDP TTL Traffic Engineering MPLS and BGP RFC s MPLS, v4.5 Generic MPLS Control and Data Plane Routing Protocol Label Distribution Protocol Routing Table () Label Mgt. Process Control Plane Routing Process Label Information Base (LIB) Routing Protocol Label Distribution Protocol MPLS Domain control packets in Data Plane MPLS Domain control packets out ed data packets in Forwarding Process Label Switching Table ed data packets out MPLS, v4.5 2 Page 85-56

57 Frame Mode MPLS for IP at LSR (Cisco) Routing Protocol Label Distribution Protocol MPLS Domain Incoming IP datagram s Incoming ed packets Routing Table () Label Mgt. Process Control Plane Data Plane Routing Process Label Information Base (LIB) Forwarding Information Base (FIB) = Optimized Cache, Cisco s CEF Label Forwarding Information Base (LFIB) = Label Switching Table e.g. IP OSPF e.g. MPLS LDP (RFC) or Cisco s TDP MPLS Domain Outgoing IP datagram s Outgoing ed packets MPLS, v4.5 3 Frame Mode MPLS for IP at Edge (LER) Routing Protocol Routing Table () Label Mgt. Process Control Plane Routing Process Label Information Base (LIB) Routing Protocol Label Distribution Protocol Incoming IP datagram s L3 lookup may point to LFIB and inserted Data Plane Forwarding Information Base (FIB) = Optimized Cache, Cisco s CEF Label Forwarding Information Base (LFIB) = Label Switching Table MPLS Domain Outgoing IP datagram s Outgoing ed packets MPLS, v4.5 4 Page 85-57

58 Frame Mode MPLS for IP at Edge (LER) 2 Routing Protocol Routing Table () Label Mgt. Process Control Plane Routing Process Label Information Base (LIB) Routing Protocol Label Distribution Protocol Outgoing IP datagram s after removal subsequent L3 lookup Data Plane Forwarding Information Base (FIB) = Optimized Cache, Cisco s CEF Label Forwarding Information Base (LFIB) = Label Switching Table MPLS Domain Incoming IP datagram s Incoming ed packets MPLS, v4.5 5 Important Databases FIB Forwarding Information Base This is the CEF database at Cisco routers Contains L2/L3 headers, IP es, s, next hop, metric The routing table is only a subset of the FIB LIB Label Information Base Contains all s and associated destinations LFIB Label Forwarding Information Base Contains selected s used for forwarding Selection based on FIB MPLS, v4.5 6 Page 85-58

59 Cisco Express Forwarding (CEF) Requirement for MPLS Forwarding information (L2-headers, es, s) are maintained in FIB for each destination Newest and fastest IOS switching method Critical in environments with frequent route changes and large s: The Internet backbone! Invented to overcome Fast Switching problems: Originally Hash table, since.2 2-way radix-tree No overlapping cache entries Any change of or ARP cache invalidates route cache First packet is always process-switched to build route cache entry Inefficient load balancing when "many hosts to one server" MPLS, v4.5 7 How CEF Works CEF "Fast Cache" consists of CEF table: Stripped-down version of the (256-way mtrie data structure) Adjacency table: Actual forwarding information (MAC, interfaces, ) CEF cache is pre-built before any packets are switched No packet needs to be process switched CEF entries never age out Any or ARP changes are immediately mapped into CEF cache CEF Table root Example-Look up " x CEF Table is built directly from the Adjacency Table is built directly from the ARP cache in case of LAN Attention: For an IP-Prefix the pointer to the Adjacency Table will start earlier in the structure Adj Tab Example-Look up " Adjacency Table E3.CF.8B Interface e/ MPLS, v4.5 8 Page 85-59

60 Label Distribution /8 exist /8 exist /8 exist /8 exist /8 exist /8 via R2 /8 via R3 /8 via R4 /8 via R5 /8 via R6 Routing Update R R2 LER FIB /8 via R3 use 89 /8 use 89 R3 LSR FIB /8 via R4 use 22 /8 use 22 R4 LSR FIB /8 via R5 use 4 LDP Binding /8 use 4 R5 LER FIB /8 via R6 no lab. R6 /8 LFIB LFIB LFIB LFIB In Out In Out In Out In Out Untag Both routing updates and LDP/TDP distribute reachability information in =, out = remote MPLS, v4.5 9 Label Switching /8 via R R R2 R3 R4 R5 R6 FIB /8 via R3 use 89 FIB /8 via R4 use 22 FIB /8 via R5 use 4 FIB /8 via R6 no lab. /8 LFIB LFIB LFIB LFIB Local Remote Local Remote Local Remote Local Remote Untag R5 must perform double lookup: LFIB tells "remove the FIB tells "use next hop R6" Label should be removed on hop earlier (by R4)!!!! MPLS, v4.5 2 Page 85-6

61 Penultimate Hop Popping /8 via R6 /8 exist Routing Update R R2 /8 use 89 R3 /8 use 22 R4 /8 do POP R5 R6 FIB /8 via R3 use 89 FIB /8 via R4 use 22 FIB /8 via R5 do POP FIB /8 via R6 no lab. /8 In - LFIB Out 89 In 89 LFIB Out 22 LFIB Last hop router (R5) tells penultimate router (R4) to remove "Penultimate Hop Popping" (PHP) Also called "Implicit Null Label" In 22 Out POP LFIB In Out implicit - null MPLS, v4.5 2 Penultimate Hop Popping 2 /8 via R R R2 R3 R4 R5 R6 FIB /8 via R3 use 89 FIB /8 via R4 use 22 FIB /8 via R5 do POP FIB /8 via R6 no lab. /8 In - LFIB Out 89 In 89 LFIB Out R5 only performs single lookup in FIB Note: PHP does not work with ATM VPI/VCI cannot be removed 22 In 22 LFIB Out POP In implicit null LFIB Out - MPLS, v Page 85-6

62 Cisco IOS Standard Behavior Routers with packet interfaces (Frame-Mode MPLS) Per-platform Label Space!!! a assigned by an LSR to a given FEC is used on all interfaces in advertisements of this LSR Unsolicited Downstream Label Distribution distribution is done unsolicited Liberal Label Retention Mode received s which are not used by a given LSR are still stored in the LIB allows faster convergence of LSP after rerouting Independent Control s are assigned by LSR independently from each other MPLS, v Cisco IOS Standard Behavior 2 Routers with ATM interfaces (Cell-Mode MPLS) Per-interface Label Space a dferent for the same FEC is used on each single interface in advertisements of this LSR Downstream On Demand Label Distribution distribution is done on request Conservative or Liberal Label Retention Mode received s which are not used by a given LSR are not stored in the LIB in case of conservative mode Independent Control MPLS, v Page 85-62

63 Cisco IOS Standard Behavior 3 ATM switches (Cell-Mode MPLS) Per-interface Label Space Downstream On Demand Label Distribution Conservative Label Retention Mode Ordered control s are assigned by LSR in a controlled fashion from egress to ingress MPLS, v Agenda Review Datagram- versus Virtual Call Service IP over WAN Problems (Traditional Approach) MPLS Principles Label Distribution Methods MPLS Details (Cisco) Internal Components MPLS in Action TDP, LDP TTL Traffic Engineering MPLS and BGP RFC s MPLS, v Page 85-63

64 Building Routing Tables /8 via R2 /8 via R3 /8 via R5 /8 R LER R2 LSR s R3 R5 LER FIB R2 Net Next Hop Label /8 R3 none R4 /8 via R3 Assumption: no PHP used LIB R2 Net Label Type LFIB R2 Label Action Next Hop Routing Protocol establish routing tables in all routers best path based on metric is stored in contains next hop information (outgoing interface) FIB additionally contains outgoing information (which can be used towards next hop) MPLS, v Allocating Labels /8 via R2 /8 via R3 /8 via R5 /8 R R2 R3 R5 FIB R2 Net Next Hop Label /8 R3 none R4 /8 via R3 LIB R2 Net Label Type / LFIB R2 Label Action Next Hop 49 untag - R2 allocates 49 to FEC /8 stored in LIB with type stores action untag in LFIB because no other router has advertised a for that FEC Every MPLS router allocates s for all IP destinations found in the routing table this is done independently from each other a has only signicance MPLS, v Page 85-64

65 Advertising and Receiving Labels via LDP /8 via R2 /8 via R3 /8 use 49 /8 use 49 /8 via R5 /8 R R2 R3 R5 LIB R Net Label Type /8 49 remote LIB R3 Net Label Type /8 49 remote /8 use 49 R4 /8 via R3 LIB R4 Net Label Type /8 49 remote - - R2 advertises 49 for FEC /8 to all neighbor routers Per platform allocation same on all interfaces LFIB may not contain an incoming interface (next HOP) field at that moment Every neighbor MPLS router stores received for IP destination /8 in the corresponding LIB MPLS, v Actions on Receiving Labels on R /8 via R2 /8 via R3 /8 use 49 /8 use 49 /8 via R5 /8 R R2 R3 R5 LIB R Net Label Type /8 49 remote - FIB R Net Next Hop Label /8 R LFIB R Label Action Next Hop - 49 R2 /8 use 49 R4 /8 via R3 R receives 49 for FEC /8 is advertised by router which is the next hop in the routing table -> therefore populates the FIB LFIB is adapted to use 49 for FEC /8 towards R2 action in LFIB has the meaning of outgoing or remote in LFIB has the meaning of incoming or MPLS, v4.5 3 Page 85-65

66 Actions on Receiving of Labels from R3 and R4 on Router R2 /8 via R2 /8 via R3 /8 use 22 /8 via R5 /8 use 22 /8 R R2 R3 R5 FIB R2 /8 use 55 R4 Net Next Hop Label /8 R3 22 /8 via R3 LIB R2 Net Label Type /8 49 /8 /8 22 remote 55 remote LFIB R2 Label Action Next Hop R3 R2 receives 22 for FEC /8 this is advertised by router which is the next hop in the routing table -> therefore populates the FIB LFIB is adapted to use (swap) 22 for FEC /8 towards R3 receives 55 for FEC /8 this is advertised by router which is not the next hop in the routing table but will be still stored in the LIB -> liberal retention mode MPLS, v4.5 3 Receiving of Labels from R2 and R3 on Router R4 /8 via R2 /8 via R3 /8 use 22 /8 via R5 /8 use 33 /8 R R2 R3 R5 Assumption: FIB R4 R4 no PHP used Net Next Hop Label /8 R3 22 /8 via R3 LIB R4 Net Label Type /8 55 /8 22 remote /8 49 remote LFIB R4 Label Action Next Hop R3 /8 use 49 /8 use 22 R4 receives 22 for FEC /8 this is advertised by router which is the next hop in the routing table-> therefore populates the FIB LFIB is adapted to use 22 for FEC /8 towards R3 already received 49 for FEC /8 this is advertised by router which is not the next hop in the routing table but will be still stored in the LIB MPLS, v Page 85-66

67 Label Switching /8 via R2 /8 via R3 /8 via R5 /8 R R R R5 FIB R2 Net Next Hop Label /8 R3 22 R4 /8 via R3 Assumption: no PHP used LIB R2 Net Label Type /8 49 /8 22 remote /8 55 remote Packets of FEC /8 will follow the corresponding Label Switched Path LFIB R2 Label Action Next Hop R3 MPLS, v Link Failure R2 <-> R3 /8 via R2 /8 via? /8 via R5 /8 R R2 R3 R5 FIB R2 Net Next Hop Label /8 R3 22 R4 /8 via R3 LIB R2 Net Label Type /8 49 /8 22 remote /8 55 remote LFIB R2 Label Action Next Hop R3 Routing protocol neighbors and LDP neighbors are lost after failure corresponding entries in FIB, LIB and LFIB are removed Traffic to FEC /8 will not be forwarded until routing table converges MPLS, v Page 85-67

68 Routing Protocol Convergence /8 via R2 /8 via R4 /8 via R5 /8 R R R R FIB R2 R4 Net Next Hop Label /8 R4 55 /8 via R3 LIB R2 Net Label Type /8 49 /8 /8 55 remote LFIB R2 Label Action Next Hop R4 After routing protocol convergence R2 can switch over immediately to other LSP alternative advertisements were stored in LIB and ed packets will flow again Otherwise R2 must wait for new bindings and can forward packets only based on IP in the meantime (action untag in LFIB) Packets of FEC /8 will follow the new Label Switched Path via R4 MPLS, v Link Failure Repair /8 via R2 /8 via R3 /8 via R5 /8... R R2 R R5 FIB R2 Net Next Hop Label /8 R3 - R4 /8 via R3 LIB R2 Net Label Type /8 49 /8 /8 55 remote LFIB R2 Label Action Next Hop 49 untag - After link repair Routing protocol neighbor detection and routing table adaptation R2 must wait for new bindings and can forward packets only based on IP in the meantime (action untag in LFIB) MPLS, v Page 85-68

69 Link Failure Repair 2 /8 via R2 /8 via R3 /8 via R5 /8 R R R R5 FIB R2 Net Next Hop Label /8 R3 22 R4 /8 via R3 LIB R2 Net Label Type /8 49 /8 22 remote /8 55 remote After LDP session to R3 is up and binding for FEC /8 from R3 received Packets of FEC /8 will follow the corresponding Label Switched Path again LFIB R2 Label Action Next Hop R3 MPLS, v Agenda Review Datagram- versus Virtual Call Service IP over WAN Problems (Traditional Approach) MPLS Principles Label Distribution Methods MPLS Details (Cisco) Internal Components MPLS in Action TDP, LDP TTL Traffic Engineering MPLS and BGP RFC s MPLS, v Page 85-69

70 TDP Key Facts Tag Distribution Protocol (TDP) invented by Cisco for distributing <, > bindings enabled by default Session establishment: UDP/TCP port 7 Hello messages via UDP destination -> well-known multicast for all subnet routers TDP session via TCP, incremental updates Not compatible with LDP but can co-exist as long as two peers use the same protocol MPLS, v LDP Key Facts Label Distribution Protocol IETF standard RFC 336 descendent of Cisco's proprietary TDP Same concept but port 646 LDP-Identier Router ID (4 bytes) Label Space ID (2 bytes) in case of per-platform space this field is set to zero note: in ATM you need a per-interface space TCP session initiated from router with highest MPLS, v4.5 4 Page 85-7

71 LDP Message Types Four basic types: Discovery (UDP): getting into contact with neighbor LSR s Adjacency (TCP): Initialization, Keepalive and Shutdown of LDP sessions Label Advertisement (TCP): Label Binding - Advertisement, - Request, - Withdrawal, - Release Notication (TCP): Signal of Error Information, Advisory Information TLV (Type/Length/Value) encoding is used for easy extension of the protocol MPLS, v4.5 4 Discovery Message Basic discovery of directly connected LSR s: Hello Message with targeted bit set to UDP to port 646 IP multicast all routers on this subnet ( ) Extended discovery of non-directly connected LSR s: Hello Message with targeted bit set to (Targeted Hello) UDP to port 646 IP unicast of neighbor used e.g. in case of MPLS Traffic Engineering After discovery LDP session is created running on top of TCP well known port 646 MPLS, v Page 85-7