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Greg.Hankins

Layer 3 Routing Over MCT

by Greg.Hankins on ‎07-29-2013 11:27 AM (231 Views)

Multi-Chassis Trunking (MCT) is a key Brocade technology that helps network operators build scalable and resilient networks, and we are continuing to add more enhancements to MCT that provide advanced redundancy.  MCT-aware routers appear as a single logical router that is part of a single link aggregation trunk interface to connected devices.  While standard LAG provides link- and module-level protection, MCT adds node-level protection, and provides sub-200 ms link failover times.  It works with existing devices that connect to MCT-aware routers and does not require any changes to the existing infrastructure. Pete Moyer wrote about the multicast over MCT features we added in NetIron software release 05.4.00 in his blog earlier this year, and we recently released version 05.5.00 with support for Layer 3 dynamic routing over MCT which is what I want to write about today.  Together these two enhancements give network operators the ability to deploy MCT Layer 3 active-active or active-passive redundancy at the network edge or border for IP unicast and multicast.

Layer 3 Routing Over MCT Highlights

  • Enables Layer 3 active-active or active-passive redundancy.
  • Supports RIP, OSPF, IS-IS, and BGP for IPv4 and IPv6 routing protocols (static routes are already supported in previous releases).
  • Supports active or passive interfaces for OSPF and IS-IS on MCT Cluster Client Edge Ports (CCEPs).
  • Provides the flexibility to run different Layer 3 protocols on MCT CCEPs and MCT Cluster Edge Port (CEP), for example OSPF on CCEPs and BGP on the CEP.
  • Provides rapid failover if one of the CCEPs or MCT routers fails; Layer 3 traffic will still be forwarded via the remaining MCT router.

Here’s how it works in a nutshell for a quick example with OSPF.  The CCEP and CEP in the diagram are on different Layer 3 networks and the routers run OSPF as the IGP.  The MCT CCEPs can be configured as active in the OSPF so that they establish an OSPF adjacency with the connected device.  Or they can be configured as passive in the IGP so that the interface is advertised via OSPF, and a static route is configured on the connected device.l3-mct.png

Layer 3 traffic that is sent to the network connected to the CEP is load-balanced over the two MCT routers by the connected device, assuming an active-active configuration. If one of the CCEPs or MCT routers fails, Layer 3 traffic will still be forwarded over the MCT Inter-Chassis Link (ICL) to the remaining MCT router.  I left out some details for simplicity to illustrate the functionality; obviously you’d want redundant connections via CEPs on each MCT router in order to provide full redundancy.

For more information on Layer 3 routing with MCT, refer to the “MCT L3 Protocols” section in the MCT chapter in the Multi-Service Switching Configuration Guide.  If you need more information on MCT then we have two technical white papers that you can read.  “Multi-Chassis Trunking for Resilient and High-Performance Network Architectures” provides an overview of the technology, and “Implementing Multi-Chassis Trunking on Brocade NetIron Platforms” has design and deployment details.