Linux File System Hierarchy

Linux File System Hierarchy is a reference that describes how the Linux Files System Hierarchy should look like. Currently, the FHS in use is at version 2.3 and was released in 2004. You can check it at http://www.pathname.com/fhs/. Most Linux distros have a policy of respecting FHS, so most users …

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, …

Per VC Frame Relay QoS

QoS parameters can be set on Frame Relay interfaces or subinterfaces using MQC commands. The disadvantage is that the policy applies to all the traffic of the interface, and not per virtual circuit (DLCI). For this purpose, the concept of Frame Relay map-classes was developed. A map-class contains configuration information …

LFI for MultiLink PPP

1.LFI for MultiLink PPP on Serial Interfaces PPP Multilink LFI (Link Fragmentation and Interleaving) allows a router to send big frames fragmented so that smaller, delay sensitive packets can be send between these fragments of larger frames. If LFI is not enabled, a packet would have to wait for the …

IP RTP Priority

1. IP RTP Reservation IP RTP Reserve adds RTP traffic to the RSVP-reserved Queues of WFQ. These queues have a weight of 128, but RTP traffic will still have to compete with other RSVP flows for the bandwidth. Additionally, traffic that exceeds the configured RTP-BW will be treated as traffic …

CBWFQ

Class Based WFQ is configured using MQC. With CBWFQ, you use the same idea of Weighted Fair Queueing, only this time, instead of using the IP_Priority to assign a weight for each flow, like in Flow-Based WFQ, you can classify traffic on different criteria and then assign a weight for …