Cisco Cisco 1700 2600 3600 3700 Series VPN Module White Paper

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Another example of multiple Cisco Virtual Switching System domains is in the area of Layer 2 adjacent WAN

deployments. It may be a requirement for the business or the applications that a routed Layer 3 WAN connection

may not be possible requiring a Layer 2 connection between two disparate geographic sites, yet still providing link

redundancy at the same time. This will ultimately require some form of Layer 2 redundancy protocol be

implemented (such as Spanning Tree Protocol), resulting in complex topologies as well as inefficient bandwidth

utilization across network links. By leveraging Cisco Virtual Switching System, such inefficiencies will be mitigated

through the formation of multichassis Cisco EtherChannel connections.

Cisco EtherChannel Concepts

Cisco EtherChannel interfaces on the Cisco Catalyst 6500 platform represent a grouping of one or more physical

ports into a single, logical port from the perspective of either a Layer 2 switching or Layer 3 routing environment.

Cisco EtherChannel interfaces allow for individual link resiliency as well as providing added bandwidth without the

necessity of complex protocols.

There are generally no restrictions with regard to which ports or modules can form members of a Cisco

EtherChannel link, except that the member interfaces need to be of the same speed and no more than 8 members

can belong to a single Cisco EtherChannel grouping. You can, therefore, extend members of the Cisco

EtherChannel interface across switching modules to allow for the maximum availability of the Cisco EtherChannel

interface if either a single link or module fails.

Traffic Distribution and Hashing

The distribution of traffic across the various members of the Cisco EtherChannel link is accomplished through

different hash schemes, each using a fixed set of fields within the frame to determine which Cisco EtherChannel

member is used to forward a particular traffic flow. With the Supervisor Engine 720-10 G, you can choose from 13

possible different hash schemes:

vss(config)#port-channel load-balance ?

dst-ip Dst IP Addr

dst-mac Dst Mac Addr

dst-mixed-ip-port Dst IP Addr and TCP/UDP Port

dst-port Dst TCP/UDP Port

mpls Load Balancing for MPLS packets

src-dst-ip Src XOR Dst IP Addr

src-dst-mac Src XOR Dst Mac Addr

src-dst-mixed-ip-port Src XOR Dst IP Addr and TCP/UDP Port

src-dst-port Src XOR Dst TCP/UDP Port

src-ip Src IP Addr

src-mac Src Mac Addr

src-mixed-ip-port Src IP Addr and TCP/UDP Port

src-port Src TCP/UDP Port