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Internet Services & Protocols

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Department of Computer Science Institute for System Architecture, Chair for Computer Networks Internet Services & Protocols IP Switching Dipl.-Inform. Stephan Groß Room: GRU314
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Department of Computer Science Institute for System Architecture, Chair for Computer Networks Internet Services & Protocols IP Switching Dipl.-Inform. Stephan Groß Room: GRU314 Dresden, June Registering for Examination Study course Type of examination Registration Process Computer Science Oral, part of Fachprüfung Individual Computational Engineering Information Systems Engineering Written test. Date: August , Time: 10:00am 11:30am Room: GRU172 Duration: 90 minutes Personal registration necessary Ms. Einer (DÜR186), Deadline: July Personal registration necessary Ms. Jarschel (GRU316b), Deadline: July Successful participation in a group homework is an indispensable requirement to get registered for the test! (This is true for all people listed in the group homework schedule on the lecture's web page.) Stephan Groß, June Internet Services & Protocols 2 Today's Agenda Introduction / motivation MPLS: components, network Traffic engineering, routing MPLS & QoS Error handling Summary and Future aspects Stephan Groß, June Internet Services & Protocols 3 Why IP switching? Internet grows within all dimensions: Data volume Number of users Number of nodes Required bandwidth ISPs demand more powerful switches & router Scalability Solution touching problems: IPv6 IP over ATM IP Switching Stephan Groß, June Internet Services & Protocols 4 IP Switching Motivation IP packet forwarding: dynamic, solid but expensive because of time costs: longest prefix match forwarding Switching technologies (e.g. ATM): fast and simple Fixed length labels for forwarding (VCI/VPI) Separation of routing and forwarding in IP networks After one-time routing fast forwarding without IP-Routing better scalability by managing labels No routing tables in nodes of the MPLS domain; only routes to the router of the domain s edges required Stephan Groß, June Internet Services & Protocols 5 IP Packet Forwarding IP forwarding per Hop for every packet on the base of: Packet header (addresses) Routing algorithm (routing table). Hop decides about next forwarding Remove layer 2 Header Longest matching prefix lookup New layer 2 header The longest matching prefix lookup can be expensive : o o big databases of prefixes (routes) Variable-length, bit-bybit comparison (max. 32 bit) Layer 2 header Layer 3 header Data Network layer (3) Link layer (2) Physicallayer (1) Stephan Groß, June Internet Services & Protocols 6 Label switching Additional tag/ label provides fast tracing of destination ports (switch/ router) can be placed in various locations to be compatible with various link & network layer technologies within layer 2 Header In a separate header between layer 2 and 3 (shim) As a part of layer 3 header Layer 2 header Layer 3 header Data Alternative positions of the label tag is a short (few-bit) identifier. only used if there is an exact match (as opposed to longest matching prefix) Stephan Groß, June Internet Services & Protocols 7 Label switching Lookup using the small tag is much faster often easy to do in hardware often don t need to involve layer 3 processing Layer 2 header Layer 3 header Data Network layer(3) Link layer (2) Physical layer(1) Stephan Groß, June Internet Services & Protocols 8 Multi-Protocol Layer Switching (MPLS) PACKET ROUTING HYBRID CIRCUIT SWITCHING IP MPLS+IP ATM Combines routing and switching functionalities and advantages Independent to layer 2 and 3 layer model Solution for any networks technologies (also LAN) Consists of separation of IP router functionality in Forwarding: forwarding of data packets (label swapping) Control: routing Protocols, signalling, management Stephan Groß, June Internet Services & Protocols 9 MPLS Terminology Label: short, IP-independent identifier, e.g. Layer 2 information (ATM VPI/VCI) Shim header (header between IP layer and layer 2 header) Label Swapping: Table lookup determines route and new labels Label Switching Routers (LSR) forwards packets along a unidirectional Label Switched Path (LSP). Label Distribution Protocol (LDP) determines LSP to destination net Forwarding Equivalence Class (FEC) describes packets with similar characteristics which may be forwarded the same way; that is, they may be bound to the same MPLS label. Stephan Groß, June Internet Services & Protocols 10 MPLS operations 1a. IP routing protocols e.g. ISIS, OSPF, BGP- Routing to destination network/node, exchange information about availability 1b. Label Distribution Protocol (LDP) Determines Label Switch Path to destination net. 4. Egress LSR removes label and delivers packet 2. Ingress Edge LSR receives packet, provides layer 3 added value services and marks packets with label 3. LSR switches packets using label swapping Stephan Groß, June Internet Services & Protocols 11 MPLS components Routing protokoll messages Routing protokoll messages Database Label Database Label Database FIB FIB FIB LIB LIB LIB Labeled packets Labeled packets LSR A LSR B LSR C MPLS Routing uses existing IP routing protocols Requires a control protocol for distributing labels between neighboured LSR Labels are stored in Label Information Bases (LIBs) MPLS Forwarding Label Swapping (exchange) and forwarding Allocation to Forward Equivalence Class (FEC) Forwarding Rules stored in Forwarding Information Base (FIB) L3 processing eventually needed at MPLS Ingress and Egress LSR Stephan Groß, June Internet Services & Protocols 12 Forwarding Equivalency Class (FEC) Packets, processed by a router in the same way Conventional routing: In a FEC all packet use the same path. The FEC is determined by processing the routing table and destination address. Packet is assigned per hop to a FEC MPLS: When a packet enters the network (Ingress LSR), the FEC is determined, e.g. similar address prefix. Packets of one FEC are assigned to the same LSP. Packet forwarding by processing labels in combination with QoS, in conformity with class of service Stephan Groß, June Internet Services & Protocols 13 MPLS Example (1) Label Switched Path: Virtual connection (path) through a MPLS network In label Address Prefix/FEC Out I face Out label In label Address Prefix/FEC Out I face Out label In label Address Prefix/FEC Out I face Out label Data Data Data Data 1 Label Switch Router (LSR): Label based packet forwarding Stephan Groß, June Internet Services & Protocols 14 MPLS Example (2) Stephan Groß, June Internet Services & Protocols 15 Label stacking Hierarchic label stack MPLS allows the usage of more then one label per packet: also called label stack. Used for nested tunnel When a new label is stacked, the packet is ruled by the new. at the end of tunnel the top LSR is removed. The packet is ruled by the following LSR. Stephan Groß, June Internet Services & Protocols 16 Hierarchic via label stack = network scalability Layer 2 header Label 3 Label 2 Label 1 IP packet Joining several paths to one path in the core reduces the number of used labels. MPLS domain 1 MPLS domain 2 MPLS domain 3 Resulting tunnel reduce routing tables. Stephan Groß, June Internet Services & Protocols 17 MPLS Signalling Protocols RSVP-TE (Resource Reservation Protocol: Traffic Extension) Mainstream protocol, used for traffic engineering Commonly used Scalable, lots of options, for MPLS extended LDP (Label Distribution Protocol) Based on TCP, except discovery function (getting neighbourhood relations) LSR sends HELLO multicast messages to known UDP port to multicast group every router in subnet LSR learn direct neighbours Establishing of a TCP LDP connection between neighboured LSRs for exchanging labels Stephan Groß, June Internet Services & Protocols 18 Label Distribution Label distribution ensures, that neighboured router uses the same data basis: FEC - Label assignment Routing table (FIB): Addr-prefix Next Hop /8 LSR2 Routing table (FIB): Addr-prefix Next Hop /8 LSR3 LSR1 LSR2 LSR3 IP Packet Label Information Base: Label-In FEC Label-Out XX /8 17 For /8 use label 17 Label Information Base: Label-In FEC Label-Out /8 XX Step 3: LSR adds Label value to FIB Step 2: LSR informs neighboured LSR about FEC and label Step 1: LSR establishes connection between FEC and label value. Label distribution is made by existing routing protocol, or label distribution protocols like LDP or RSVP-TE. Stephan Groß, June Internet Services & Protocols 19 MPLS Applications Traffic Engineering Problem: Shortest-Path Routing results in overloaded links, while other links are less used. Establishing of LSPs for specified (aggregated) flows Load Balancing Generate one FEC for several LSPs Change between LSPs - Rerouting Virtual private network Forwarding between subnetworks using labels Replacement for IP-in-IP-tunnel Extend label stacks QoS support Resource reservation (DiffServ, ATM) for specified LSPs Rerouting when a link fails Establish more LSPs for one FEC and switch if a error occurs (Backups FRR) Establish bypass LSPs (Rerouting) Stephan Groß, June Internet Services & Protocols 20 MPLS Traffic Engineering Targets Distribute traffic to available resources efficiently Controlled usage of resources Fast reaction if network topology changes L S R MPLS - Traffic Engineering Explicit routing or constraint-based routing allows generating paths with regards to any requirements Distribute packet flows (not only shortest path ) Reserve network resources Protocols: CR-LDP, RSVP LSP tunnel or paths are uni-directional point-to-point connections L S R L S R L S R L S R Stephan Groß, June Internet Services & Protocols 21 Explicit Routing LSP route is defined by ingress node. 1. Label request message contains ER path B,C,D 2. Request message is processed, next node is determined. Path lists are modified to C,D 3. Request message terminates. 6. If LER A receives label mapping path is established. 5. LSR C receives label to transmit data to LER D. LIB is refreshed. 4. Label mapping message is generated LER A LSR B LSR C LER D Ingress ER Label Egress Switched Path Stephan Groß, June Internet Services & Protocols 22 MPLS QoS Explicit path makes associations of special resource requirements possible: Bandwidth, delay Router maintenance LSP Main target: supporting Diff-Serv QoS model: Ensure, that DSCP marked packets get the same QoS in every LSR network IP header contains DSCP; DSCP does not affect forwarding Per-Hop-Behavior must be deducted from the label header Usage of EXP field in Shim Header (3 Bit), E-LSP Deduce PHB direct from label (in MPLS without Shim Header like ATM) Stephan Groß, June Internet Services & Protocols 23 Error Correction Why MPLS Error correction? Rises reliability of the network, because of fast reactions without or with little information loss when error occur IP Routing Protocols are solid on the one hand, on the other hand error correction/ Rerouting is to slow (several sec. IGP, several min. BGP) Not suitable for applications like VPNs, VoIP etc., delays 10 ms not acceptable IP routing has no error correction/ Rerouting in regard to bandwidth requirements etc. (e.g. bandwidth old path = bandwidth new path) MPLS provides fast reaction if error occur (fail of nodes or links) MPLS carries on providing priority allocations for VPNs,VoIP etc. Rerouting: On Demand, if error occur (or for optimisation) a new path is established with the help of a signalling protocol (without handover if possible) Protection Switching or Fast ReRoute (FRR): Additional backup LSP s (hop path, whole path), permanent Established by signalling when primary LSPs are initialised Stephan Groß, June Internet Services & Protocols 24 Rerouting RSVP-TE (1) R8 R3 R9 R4 R2 Pop R R6 R7 32 R5 22 Actual Path ( R1- R2- R6- R7- R4- R9) R1 initiates new path (R1- R2- R3- R4- R9) sending path message While R9 does not receive a path message, the actual is reservation hold (refreshed) Stephan Groß, June Internet Services & Protocols 25 Rerouting RSVP-TE (2) R1 R8 R R6 R3 26 R4 R7 32 R9 R5 22 Resv: allocates Label for both paths and resources if necessary PathTear can free allocated resources if the network is optimised. In the case of errors softstates expires after timeout. Stephan Groß, June Internet Services & Protocols 26 Fast Reroute Client Tunnel choice IP/MPLS Backbone Primary TE tunnel Client Client (Provider Edge PE) PE Client Backup TE tunnel established before error situation Fast Reroute allows to locally patch traffic onto a backup tunnel in case of a link or node failure until a more appropriate backup path has been established. 1. Primary TE-tunnel transmits data of various clients if an error occurs (e.g. Link fail) straight after PE, backup TE tunnel is activated and layer 2 connections (e.g. ATM, GE,etc) are rerouted over the backup tunnel (LSP). 2. Fast Reroute reactivates connections in 50 ms. Stephan Groß, June Internet Services & Protocols 27 MPLS Standards RFC 2547 BGP/MPLS VPNs. E. Rosen, Y. Rekhter. March RFC 2702 Requirements for Traffic Engineering Over MPLS. D. Awduche et al. September 1999 RFC 2917 A Core MPLS IP VPN Architecture. K. Muthukrishnan, A. Malis. September 2000 RFC 3031 Multiprotocol Label Switching Architecture. E. Rosen, A. Viswanathan, R. Callon. January 2001 RFC 3032 MPLS Label Stack Encoding. E. Rosen, D. Tappan, G. Fedorkow, Y. Rekhter, D. Farinacci, T. Li, A. Conta. January 2001 RFC 3035 MPLS using LDP and ATM VC Switching. B. Davie, J. Lawrence, K. McCloghrie, E. Rosen, G. Swallow, Y. Rekhter, P. Doolan. January 2001 RFC 3270 Multi-Protocol Label Switching (MPLS) Support of Differentiated Services. F. Le Faucheur et al May 2002 RFC 3468 The Multiprotocol Label Switching (MPLS) Working Group decision on MPLS signaling protocols. L. Andersson, G. Swallow. February 2003 RFC 3469 Framework for Multi-Protocol Label Switching (MPLS)-based Recovery. V. Sharma, Ed., F. Hellstrand, Ed. February 2003 Stephan Groß, June Internet Services & Protocols 28 Provider and MPLS Americas EMEA AsiaPac/Japan Some 200 Customers (MPLS Core & L2/L3 Edge) Stephan Groß, June Internet Services & Protocols 29 EBT Korea Telecom Source: Cisco Summary MPLS Two directions of development: New application/services VPN, Diffserv TE, L2 Transport Generalization of MPLS TE (Generalized MPLS - GMPLS), e.g. for optical technologies Positive aspects through MPLS Router performance overtops ATM switches Constraint-based routing in IP networks intra-domain TE Universal IP control layer IP and optical connections Fast Restoration no longer depends on SONET/SDH back to the basics - IP solutions are reanimated Not so positive aspects because of MPLS Emotional IP-is-the-only-way optimism manufacturer/ seller must provide new solutions: IPv4 and MPLS control and forwarding Missing network management lots of competitive standards Stephan Groß, June Internet Services & Protocols 30
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