Virtual LAN as A Network Control Mechanism

EdgeNet2006 Summit 1

Virtual LAN as A Network Control Mechanism

Tzi-cker Chiueh

Computer Science Department

Stony Brook University


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


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


VLAN in Practice802.1Q tag is added at the hosts or edge switchesPackets are exchanged between two VLANs through a routerConceptually, each VLAN is like a physical LAN that has its own Spanning tree L2 routing table

802.1S allows per-VLAN spanning treeNumber of VLANs supported in real switches is hundredsVLAN specification is port-based or host-based

Configuration can be based on SNMP or web requests or CLI


Viking Project

Goal: A network resource management system for campus-wide L2 network backbone or Metro Ethernet ServicesA 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


Problem with Existing Ethernet

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


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 EthernetNeed to combine multiple logical VLANs into one physical VLAN, which corresponds to a spanning tree; active and path paths belong to different VLANs


Big Picture

Each host in a single IP subnet participates in multiple VLANs, and uses different VLANs to reach different destinationFast 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


IGMP SnoopingWhy: Avoid using L2 broadcast when supporting L3 multicastHow: Snoop on IGMP packets to infer a L2 distribution tree for an IP multicast group on top of a L2 network’s spanning treeSupported 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


Cassini Project

Goal: Leverage commodity Ethernet switches as building block for storage area network Multicast is an important primitiveIdea: Use VLAN/IGMP snooping to support tree-based L2 multicastTransparent Reliable Multicast: Multiple L3 connections (e.g. TCP) layered on on

top of a L2 multicast connection ACK/Retransmission on individual L3 unicast

connection


Conclusion

Many innovative features in commodity Ethernet switches that are largely exploitedCLI or SNMP or HTTP provides the possibility of on-the-fly reconfiguration according to workloads and/or hardware health statusInteresting application scenarios: Large-scale L2 network Storage area network Compute cluster interconnect: program-specific

topology


Thank You!

Questions?


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 loggingScalable multicast state management

Virtual LAN as A Network Control Mechanism

Documents

Transcript of Virtual LAN as A Network Control Mechanism