CCIE RS – Written – L2 – Describe Chassis Virtualization and Aggregation Technologies

Describe Chassis Virtualization and Aggregation Technologies


Multichassis Etherchannel

  • Interchassis redundancy mechanism, dual home
    • Points of Attachment (PoAs)
  • Multichassis LCAP (mLACP) – Enhancements to 802.3ad (LACP)
  • Lacp max-bundle -> must be configured on all POAs
  • DHD – Dual Homed Device

Restrictions for mLACP

  • mLACP does not support Fast Ethernet.
  • mLACP does not support half-duplex links.
  • mLACP does not support multiple neighbors.
  • Converting a port channel to mLACP can cause a service disruption.
  • The maximum number of member links per LAG per PoA is restricted by the maximum number of ports per port channel, as limited by the platform.
  • System priority on a DHD must be a lesser priority than on PoAs.
  • MAC Tunneling Protocol (MTP) supports only one member link in a port channel.
  • A port-channel or its member links may flap while LACP stabilizes.
  • DHD-based control does not function when min-links is not configured.
  • DHD-controlled revertive behavior with min-links is not supported.
  • Brute-force failover always causes min-link failures.
  • Any failure with brute-force failover behaves revertive.


  • 510 user configurable etherchannels
  • 128 on code older than 12.2(33)

VSS Concepts

Virtual Switching Systems

  • Combines pair of 6500 into a single network element
  • Manages redundant links
    • Act as single port channel
  • Reduces number of L3 neighbors and providing loop-free L2 topology

Activeand Standby Chassis

  • Active controls the VSS
  • Runs L2 and L3 control protocols
  • Provides management functions
  • Both perform packet forwarding
  • Standby sends all control traffic to active chassis for processing

Virtual Switch Link (VSL)

  • Separate link that carries control and data traffic between 2 chassis of VSS
  • VSL removes existing config from interfaces

Alternative to STP

This is a very broad heading. This could be relating to multichassis etherchannel or VPC or Stackwise virtual (recent feature in newer switches)

This could also be referencing an old feature – Flex Links

This would allow you to configure a backup port, if the primary connection would go down the secondary port would be enabled and that interface would continue to forward the traffic. Preemption could be configured to allow the primary interface to take over the traffic forwarding if it recovered.


Stackwise is a technology that allows you to connect up to 9 (like) switches to form one large logical switch. The switches connect using backplane ports and are managed by the master switch, determined by election during the switches boot process.

Master Switch Election

  1. User priority – Manually configure the switch that will be the master
  2. Hardware/Software Priority – Default to switch with most features (IP services over IP base). Highest priority wins
  3. Default configuration – configured switches takes priority over non-configured switch
  4. Uptime – Longest uptime
  5. MAC Address – lowest mac address is selected

IOS images must match

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