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Christophe Jelger Post-doctoral researcher Christophe.Jelger@unibas.ch

Routing, Addressing, and Naming Switching in the Internet. Christophe Jelger Post-doctoral researcher Christophe.Jelger@unibas.ch. Today's lecture. MPLS: MultiProtocol Label Switching. Metropolitan Ethernet. The Spanning Tree Protocol (SPT) for Ethernet networks.

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Christophe Jelger Post-doctoral researcher Christophe.Jelger@unibas.ch

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  1. Routing, Addressing, and NamingSwitching in the Internet Christophe Jelger Post-doctoral researcher Christophe.Jelger@unibas.ch Christophe Jelger – CS221 Network and Security - Universität Basel - 2005

  2. Today's lecture • MPLS: MultiProtocol Label Switching. • Metropolitan Ethernet. • The Spanning Tree Protocol (SPT) for Ethernet networks. Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  3. MPLS: MultiProtocol Label Switching (1) • What is it all about? • The Internet grew from circuit-switched (telephone) networks to packet switched networks. • Telcos were offering leased lines to inter-connect networks located at different locations (e.g. the world-wide branches of a large company). • Circuit-switching was very well known and provided a clear separation of services with different levels of quality. • Circuit-switching was offering a higher level of control in the core of the ISPs' networks. • Technologies like ATM were offering virtual circuits and a relatively high level of traffic enginneering capabilities. • With the growth of IP, telcos/ISPs needed a new technology to provide this kind of services in an IP-friendly manner. Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  4. MPLS: MultiProtocol Label Switching (2) • History: MPLS was hence initially designed to: • Provide a more IP-friendly data-carrying technology than ATM. • Running IP over ATM was complex, and ATM small cells (53 bytes) were becoming an overhead when carrying potentially large IP packets. • Allow the creation of simple high-speed "IP switches". • At that time, IP forwarding was not entirely feasible in hardware (because of the longest-prefix-match forwarding scheme). • No longer an issue in modern routers, although "switching is still faster than routing". • Create a "shim" 2.5 layer to unify data-carrying technologies. • MPLS used over existing ATM and FrameRelay infrastructures. • IP used directly over MPLS. Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  5. MPLS: MultiProtocol Label Switching (3) • What is the goal of MPLS today? • ISPs need to separate/isolate different kinds of traffic (IP, voice, video, business-critical applications, etc) in their core network(s). In practice, MPLS is used to provide: • Virtual Private Networks (VPNs). • Quality of Services (e.g. guaranteed bandwidth between some points in the network). • Traffic Enginnering (e.g. load balance traffic over all links of a network). • To do this, MPLS introduces the notion of FEC: Forwarding Equivalence Class. • A FEC is a group of IP packets which are forwarded in the same manner inside an MPLS network. • In practice, a classifier inspects each IP packet entering an MPLS network and decides to which FEC it belongs. Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  6. MPLS: MultiProtocol Label Switching (4) • How does it work? • MPLS uses label switching to forward packets. • Fowarding is based on "exact match": this is much faster than IP's longest-prefix match. • A label is a short (4 bytes) locally-significant identifier used to identify a Forwarding Equivalence Class (FEC). MPLS labels have the following format: • label value: 20 bits, unstructured (flat) • exp: 3 bits, currently used as Class of Service (CoS) field • S bit: "bottom of stack" indicator (when labels are stacked) • Time To Live: 8 bits. label value exp S TTL 32 bits Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  7. MPLS: MultiProtocol Label Switching (5) • The forwarding of packets inside an MPLS network. • Labels are used to identify Label-Switched Paths (LSPs). • The mapping between IP packets – FECs and LSPs is done by Label Switched Routers (LSRs) at the edges of the MPLS network. 13 → pop, oif:1 Packets for 10.1.2.3.0/24 (blue) 10.1.2.4.0/24 (red) Forwarding is based on label 1 13 Ingress LSR subnet 10.1.3.0/24 1 Egress LSR 17 1 21 2 44 subnet 10.1.2.0/24 Assigns each IP packet to the appropriate FEC and adds appropriate label to IP packet 17 → swap(13), oif:1 21 → swap(44), oif:2 1 44 → pop, oif:1 subnet 10.1.4.0/24 10.1.3.0/24 → push(17), oif:1 10.1.4.0/24 → push(21), oif:1 Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  8. MPLS: MultiProtocol Label Switching (6) • The forwarding of packets inside an MPLS network. • FECs can be encasulated inside other FECs: we end up with stacks of labels. This is useful to create "trunks" and reduce state in the core MPLS network. Packets for 10.1.2.3.0/24 (blue) 10.1.2.4.0/24 (red) 13 → pop, oif:1 Forwarding is based on label 1 17 13 subnet 10.1.3.0/24 1 11 17 6 17 1 1 6 21 11 21 2 21 44 6 → swap(11), oif:1 11 → pop 17 → swap(13), oif:1 21 → swap(44), oif:2 1 17 → push(6), oif:1 21 → push(6), oif:1 44 → pop, oif:1 subnet 10.1.4.0/24 Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  9. MPLS: MultiProtocol Label Switching (7) • The distribution of labels. • For each hop, the label is chosen by the downstream LSR and passed to the upstream LSR. Hence labels are distributed "against the flow of packets". • The distribution of labels can be done "in collaboration" with an intra-domain routing protocol like OSPF or IS-IS. • There are currently 2 protocols to distribute labels: • LDP: Label Distribution Protocol. • RSVP-TE: Resource reSerVation Protocol for Traffic Engineering. Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  10. MPLS: MultiProtocol Label Switching (8) • The distribution of labels. • A simplified example. The LSR chooses a label 13 → pop, oif:1 Request PATH: 10.1.3.0/24 Reply RESV: label 13 Reply RESV: label 17 Request PATH: 10.1.3.0/24 1 Ingress LSR subnet 10.1.3.0/24 1 Egress LSR 1 2 subnet 10.1.2.0/24 17 → swap(13), oif:1 1 The LSR chooses a label 10.1.3.0/24 → push(17), oif:1 subnet 10.1.4.0/24 Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  11. MPLS: MultiProtocol Label Switching (9) • MPLS in the Internet today. • MPLS is used extensively by most ISPs. An extended version called GMPLS (Generalized MPLS) is also used to setup LSPs over optical fiber technologies (SONET/SDH and DWDM). • With "Metro Ethernet" networks, MPLS is used to provide "pseudowires" between Ethernet switched networks. • MPLS is still evolving: the IETF mpls working group is very active, with many internet drafts still active and various mechanisms still being standardized (e.g. lsp-ping, security, network management, etc). Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  12. Metro/Carrier Ethernet (1) • According to some studies, 95% of today's Internet traffic starts and ends as Ethernet (end-sites are using Ethernet networks). • In the mean time, ISPs/carriers used everything but Ethernet in their backbone networks. • Ethernet is becoming extremely cheap with very high data rates. • In contrast, data carrying technologies (SONET/SDH, MPLS) are relatively expensive. • 10 Gb/s already there, 40 Gb/s and 100 Gb/s are on their way. • However, Ethernet is too "dumb" for carriers. • Backbone networks require advanced services like QoS, network management, traffic engineering, etc. Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  13. Metro/Carrier Ethernet (2) • Metro/Carrier Ethernet is a set of technologies and products. • The terms "metro" and "carrier" are more or less used to describe the same technologies. However "metro" is targeted more at customers networks, while "carrier" is targeted more at ISPs. • Many manufacturers, standards, and deployment styles. • Common denominator is Ethernet: for example, one typical obejctive is to inter-connect Ethernet VLANs via a backbone network (e.g. to inter-connect the networks located at different branches of a large organization). Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  14. Metro/Carrier Ethernet (3) • Metro/Carrier Ethernet: some protocols. • IEEE 802.1Q tunneling, or "tag stacking", or "QinQ". • Very similar to MPLS labeling and label stacking, but with Ethernet VLAN tagging technologies: the goal is to inter-connect customers' VLANs without any "collision of VLAN ids/tags". Image from: http://www.cisco.com/warp/public/cc/pd/si/casi/ca6000/prodlit/65met_wp.htm Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  15. Metro/Carrier Ethernet (4) • Metro/Carrier Ethernet: some protocols. • IEEE 802.1Q tunneling, or "tag stacking", or "QinQ". • Also known as 802.1ad or "Provider bridges". CPE = Customer Premises Equipment PE = Provider Edge Image from: http://www.cisco.com/warp/public/cc/pd/si/casi/ca6000/prodlit/65met_wp.htm Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  16. Metro/Carrier Ethernet (5) • Metro/Carrier Ethernet: scalability. • QinQ is limited to 4094 tags/customers, and there is a scalability issue with the size of forwarding tables. • To remediate this, new standards have been defined: • IEEE 802.1ah or "Backbone Provider Bridges" or "MAC-in-MAC". • Introduces encapsulation techniques of Ethernet in Ethernet. • IEEE 802.1Qay-TE: a carrier grade extension of 802.1ah with traffic engineering, MPLS compatibility, deterministic delivery. • HVLAN: proposed extension to introduce hierarchical VLAN tagging with a CIDR-style "bast match" forwarding. • Sound like re-inventing the wheel? • New variants (with new names) of MPLS, IP, SONET, ATM? Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  17. Metro/Carrier Ethernet (6) • Currently an extremely active area. • Plenty standards on their way. • IETF vs. IEEE battle. • Vendors battle with competing technologies and protocols. • Development seems to be fully driven by the market (and not always by technical advances). • ISPs want to save cost to extend their infrastructures. • Customers want to pay less. • Vendors want to sell new equipments. • Network deployments is really becoming "à la carte": • e.g. MPLS over Ethernet? Eth. over MPLS? Eth. over MPLS over Eth.? • A palette of technologies, costs, and services. Not clear who wins … Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  18. The spanning tree protocol (SPT). • A spanning tree of a graph is a sub-graph that contains all the vertices (nodes) and is a tree. • Note that a given graph usually have multiple spanning trees. Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  19. The spanning tree protocol (2). • In a bridged Ethernet network, the main objective of STP is to prevent loops in a topology with redundant paths. • How? Redundant links are de-activated (for forwarding). • One goal is to prevent the "broadcast storm problem". Broadcast loop Loop is prevented A A ARP REQ B? ARP REQ B? B B Ethernet switch. Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  20. The spanning tree protocol (3). • Another goal is to prevent duplicate frames to be received. A data sent to B B Duplicate frame is received! Ethernet switch. Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  21. The spanning tree protocol (4). • Loops also generate inconsistent and unstable states. • e.g. a switch learns on which port a machine is connected by looking at the source MAC address of Ethernet frames. Switch learns A is on right port Switch learns A is on left port A data sent to B B Ethernet switch. • Also note: Ethernet frames have no TTL ! • i.e. they can potentially re-circulate forever! Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  22. The spanning tree protocol (5). • Centralized algorithms are not desirable in practice but are interesting to study the problem. • E.g. Kruskal, Prim, Boruvka, and Dijkstra algorithms. • Challenges for distributed algorithms: • To converge (!): only one active spanning tree during steady-state. • To converge rapidly after topology change (Rapid STP). • Should remain simple for low-cost implementation. • Very old and well studied algorithm. • For Ethernet, it is standardized today by IEEE 802.1D (1990). • Since 2004, RSTP replaces STP in the standard. Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  23. The spanning tree protocol (6). • Basic operation of STP: All switches participating in STP gather information on other switches in the network through an exchange of data messages. • These messages are bridge protocol data units (BPDUs). This exchange of messages results in the following: • The election of a unique root switch. • The election of a designated switch for every switched LAN segment. • The removal of loops in the switched network by placing redundant switch ports in a backup state. • The root switch is the logical center of the spanning-tree topology. All paths that are not needed to reach the root switch from anywhere in the switched network are placed in backup mode. Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  24. The spanning tree protocol (7). • Electing a root bridge. • Each switch has a MAC address and a configurable priority number; both of these numbers make up the Bridge Identification or BID. • The BID is used to elect a root bridge based upon the lowest priority number; if this is a tie then the numerically lowest MAC address wins. • Upon startup all bridges send BPDUs. Once found, only the root bridge sends BPDUs (e.g. every 2 seconds). • Typical forwarding algo: Forward a BPDU if and only if BID < my_BID.Stop sending my own BPDUs if I see BPDUs with BID < my_BID. Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  25. The spanning tree protocol (8). • Format for the BID. Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  26. The spanning tree protocol (9). • Finding shortest paths to the root bridge. • Each bridge must keep one and only one active link to the root bridge. • Link with lowest cost is kept as root link (root port). • Redundant links are blocked. • Shortest path is based on cumulative link cost. • Link costs are based on the speed of the link. Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  27. The spanning tree protocol (10). Root port Root port Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  28. The spanning tree protocol (11). • Electing a designated port for each segment. • Port announcing lowest cost is elected as designated port for segment. Root port Root port Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  29. The spanning tree protocol (12). • After convergence is reached there is: • One spanning tree per Ethernet network. • One root bridge. • One root port per non-root bridge. • One designated port per segment. • All other ports are blocked. • Note that it's possible to have one spanning tree per Ethernet VLAN. Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  30. The spanning tree protocol (13). • In 2004 STP is replaced in the standard by Rapid STP. • Convergence of STP takes up to 50 seconds. • Detection of lost BPDUs = 20 seconds (=root bridge lost). • Listening phase (no data forwarding) = 15 seconds. • Learning phase (no data forwarding) = 15 seconds. • Changes introduced by RSTP are • All bridges periodically generate BPDUs: costs are updated more rapidly. • Links are point-to-point, edge-type, shared: failures are detected more rapidly (e.g. non bridge-to-bridge ports are ignored). • Network convergence is up to 15 seconds. Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  31. The rapid spanning tree protocol (14). Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

  32. Thank you Questions? Christophe Jelger – cs321 Autonomic Computer Systems – UniversitätBasel - 2009

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