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Virtual LAN as A Network Control Mechanism

Learn about Virtual LAN (VLAN) as a network control mechanism, IEEE 802.1Q specifications, IGMP Snooping, Traffic Engineering, and more. Explore how VLANs are implemented in practice and the benefits they offer for large-scale L2 networks. Discover new approaches for network control and traffic management in commodity Ethernet switches.

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Virtual LAN as A Network Control Mechanism

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  1. Virtual LAN as A Network Control Mechanism Tzi-cker Chiueh Computer Science Department Stony Brook University EdgeNet2006 Summit

  2. Ethernet Routing • Spanning tree topology • Source Learning to populate the forwarding table • Broadcast if don’t know what to do • Question: How to control the routes on large L2 networks of commodity Ethernet switches? VLAN EdgeNet2006 Summit

  3. Virtual LAN (IEEE 802.1Q) • Originally proposed to support multiple IP subnets on a L2 network without L3 routers • VLAN limits the scope of a broadcast packet • 4-byte 802.1Q header inserted between SRC MAC and Type/Length • 2-byte 802.1Q tag type = 0x8100 • 3 bits for priority (IEEE 802.1P) • 1 bit for Canonical Format Indicator • 12 bits for VLAN ID EdgeNet2006 Summit

  4. EdgeNet2006 Summit

  5. VLAN in Practice • 802.1Q tag is added at the hosts or edge switches • Packets are exchanged between two VLANs through a router • Conceptually, each VLAN is like a physical LAN that has its own • Spanning tree • L2 routing table • 802.1S allows per-VLAN spanning tree • Number of VLANs supported in real switches is hundreds • VLAN specification is port-based or host-based • Configuration can be based on SNMP or web requests or CLI EdgeNet2006 Summit

  6. Viking Project • Goal: A network resource management system for campus-wide L2 network backbone or Metro Ethernet Services • A large number of low-port-density switches vs. a small number of high-port-density switches • Larger geographic coverage • More cost-effective (economy of scales) • More redundancy at the physical connectivity level • Higher aggregate back-plane throughput EdgeNet2006 Summit

  7. Problem with Existing Ethernet • Main problem: single spanning tree • Inefficient • Inflexible routing • Longer failure recovery EdgeNet2006 Summit

  8. Traffic Engineering • Constantly measure traffic load matrix • Compute an active-backup path for each node pair to balance loads among links and use shorter links whenever possible mesh rather than tree • Force a path’s route by setting up a dedicated logical VLAN for it  ATM-like behavior on Ethernet • Need to combine multiple logical VLANs into one physical VLAN, which corresponds to a spanning tree; active and path paths belong to different VLANs EdgeNet2006 Summit

  9. Big Picture • Each host in a single IP subnet participates in multiple VLANs, and uses different VLANs to reach different destination • Fast failure recovery: Switch to a different 802.1S VLAN to reach a destination when the current VLAN fails • The failure recovery time of the Viking prototype is less than 500 msec, most of which is SNMP trap • Next step: Edge-based traffic shaping and 802.1P for QoS guarantee EdgeNet2006 Summit

  10. EdgeNet2006 Summit

  11. IGMP Snooping • Why: Avoid using L2 broadcast when supporting L3 multicast • How: Snoop on IGMP packets to infer a L2 distribution tree for an IP multicast group on top of a L2 network’s spanning tree • Supported by most commodity Ethernet switches • Real switches can only track a small number of IP multicast groups • Configuration: Sending IGMP packets to the root, which acts as the default router EdgeNet2006 Summit

  12. Cassini Project • Goal: Leverage commodity Ethernet switches as building block for storage area network • Multicast is an important primitive • Idea: Use VLAN/IGMP snooping to support tree-based L2 multicast • Transparent Reliable Multicast: • Multiple L3 connections (e.g. TCP) layered on on top of a L2 multicast connection • ACK/Retransmission on individual L3 unicast connection EdgeNet2006 Summit

  13. EdgeNet2006 Summit

  14. Conclusion • Many innovative features in commodity Ethernet switches that are largely exploited • CLI or SNMP or HTTP provides the possibility of on-the-fly reconfiguration according to workloads and/or hardware health status • Interesting application scenarios: • Large-scale L2 network • Storage area network • Compute cluster interconnect: program-specific topology EdgeNet2006 Summit

  15. Thank You! Questions? EdgeNet2006 Summit

  16. Mariner Project • Goal: Leverage advanced features of commodity Gigabit Ethernet switches to build scalable compute cluster interconnects (~1000 nodes) • Programmable application-specific interconnect topology • Fault management: asynchronous state check-pointing and pessimistic message logging • Scalable multicast state management EdgeNet2006 Summit

  17. EdgeNet2006 Summit

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