Virtual LAN as A Network Control Mechanism

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Virtual LAN as A Network Control Mechanism

• Tzi-cker Chiueh
• Computer Science Department
• Stony Brook University

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Ethernet Routing

• Spanning tree topology
• Source Learning to populate the forwarding table
• Broadcast if dont know what to do
• Question How to control the routes on large L2
  networks of commodity Ethernet switches? VLAN

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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

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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

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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

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Problem with Existing Ethernet

• Main problem single spanning tree
• Inefficient
• Inflexible routing
• Longer failure recovery

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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 paths 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

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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

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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 networks 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

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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

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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

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Thank You! Questions?
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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

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