Rate Limiting of RPF Failure Traffic

When you enable rate limiting of packets that fail the RPF check (non-RPF packets), most non-RPF packets are dropped in hardware. According to the multicast protocol specification, the router needs to receive the non-RPF packets for the PIM assert mechanism to function properly, so all non-RPF packets cannot be dropped in hardware. When a non-RPF packet is received, a NetFlow entry is created for each non-RPF flow. When the first non-RPF packet arrives, the PFC bridges the pa..

Load Balancing Across PortChannels

When a switch decides to forward a frame out a PortChannel, the switch must also decide which physical link to use to send each frame. To use the multiple links, Cisco switches load balance the traffic over the links in an EtherChannel based on the switch’s global load-balancing configuration. Load-balancing methods differ depending on the model of switch and software revision. Generally, load balancing is based on the contents of the Layer 2, 3, and/or 4 headers. If load ..

Forming PIM Adjacencies Using PIM Hello Messages

PIM routers form adjacencies with neighboring PIM routers for the same general reasons, and with the same general mechanisms, as many other routing protocols. PIMv2, the current version of PIM, sends Hello messages every 30 seconds (default) on every interface on which PIM is configured. By receiving Hellos on the same interface, routers discover neighbors, establish adjacency, and maintain adjacency. PIMv2 Hellos use IP protocol number 103 and reserved multicast destination ..

Network Design Elements

Multiplexing is a fundamental element of network design. Indeed, you could argue that a network is typically one huge multiplexing system. More specifically, however, multiplexing is a tool that provides economies of scale—multiple users share one large resource rather than a number of individual resources.  NOTE  Multiplexing is the aggregation of multiple independent traffic flows into one large traffic flow. A useful analogy is the freeway system, which mul..

Detecting Error Conditions

 By default, a Catalyst switch detects an error condition on every switch port for every possible cause. If an error condition is detected, the switch port is put into the errdisable state and is disabled. You can tune this behavior on a global basis so that only certain causes trigger any port being disabled. Use the following command in global configuration mode, where the no keyword is added to disable the specified cause: Switch(config)# [no] errdisable detect cause ..