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Routing & Switching

NetFlow 102 – FNF – Flexible NetFlow

Netflow configuration is different by platform and IOS version. Initially, Cisco IOS supported what is now known as “Traditional/Original Netflow(TNF)”, but newer versions of the IOS support “Flexible Netflow (FNF). Support for Traditional Netflow configuration is being dropped from neweer IOS versions, so if available, use Flexible Netflow configuration on …

How CEF works

1. Process Switching 1.1 How it works Network interface detects a new packet on the wire. The interface will receive the packet and will place it in the I/O memory. It will then send a “receive interrupt” to the processor to indicate that a new packet needs to be switched. …

MPLS L3 VPN

This article assumes the “provider” network already has an IGP in place and that the LDP is configured to advertise label bindings between LSRs. Check MPLS 101 on how to do that. 1. Verify LDP is working within provider network One common mistake when configuring L3 MPLS VPN appears when …

IS-IS Mechanics – CLNP

1. ISO OSI Terminology ISO OSI term TCP/IP Equivalent End System Host Intermediate System Router Circuit Interface Area Area Domain Autonomous System IS-IS = Intermediate System to Intermediate System CLNP = Connection-Less Network Protocol = Layer 3 network protocol that is used to communicate between ESes. CLNP offers a CLNS …

IS-IS 101

1. Starting the routing process Starting IS-IS process requires a 2 step configuration: 1. In the global config 2. On the interfaces that will be enabled for IS-IS 1.2 Passive interface The passive interface command in IS-IS has a basically an opposite meaning to what it means in the other …

PfR 101 – Perfromance Routing

1. PfR Technology PfR stands for Performance Routing, but the feature was first called OER (Optimized Edge Routing). This is why most commands still start with the oer keyword. The idea behind PfR is to have a controlling entity (Master Controller) that takes over routing decisions for one or more …

NSF – Non Stop Forwarding

1. What is NSF NSF is a feature that allows routers to keep on forwarding traffic (non stop forwarding) even in the event of a restart. This is done by separating the control and the data plane, having one process involved in building the routing table and another process in …

BFD – Bidirectional Forwarding Detection

1. What is BFD? BFD stands for Bidirectional Forwarding Detection and it’s a protocol that is used for rapid detection of link failures when the line-protocol is still “up”. BFD is enabled on interface and creates a BFD session with the neighboring router (BFD Peer). Routing protocols such as EIGRP, …

Routing Order of Operations

The original information was taken from Cisco article on NAT Order of Operations. However, this order helps understand other features, like WCCP. 1. Routing Order of Operations If IPSec then check input access list decryption – for CET (Cisco Encryption Technology) or IPSec check input access list check URPF (Unicast …

MTU 101

MTU stands for Maximum Transmission Unit. This is the amount of data that can be transmitted by one protocol. MTU is used at every layer of the OSI stack, but it’s value is closely related to the layer/protocol. 1. On a router 1.1 Layer 2 – mtu On a router, …