Currently browsing category

2 IPv4

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. …

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 …

Tunnel Interfaces

1. Tunnel Modes A tunnel makes two distant devices appear directly connected over a logical interface. When a packet is sent out on the tunnel interface, it is encapsulated in the “carrier” protocol and sent over a physical interface.The most used carrier protocols are GRE, IP-in-IP and IPv6, and this …

More BGP

1. Route Dampening It is used to stop unstable routes from being forwarded throughout the network. When a route flaps, a penalty is assigned to the route (Default: 1000 per flap). A timer called Half-Life is used to reduce the penalty value to half (Default: 15 min). If the penalty …

IPv4 101

1. Setting an IP Address Any combination of IP-ADDR and NETMASK can be used as long as the host portion of the address is not all zeros. One exception is allowed, when using a /31 mask. By default, the router will accept combinations that result in a subnet portion of …