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Virtual Routing and Forwarding basics (VRF)

by ShahedSeptember 1, 2011October 24, 20150

Virtual Routing and Forwarding basics (VRF): Today i will discuss about Virtual Routing and Forwarding basics (VRF). VRF is a Layer 3 VPN technique. VRF can be use with or without MPLS. If we look bellow diagram we see here two VRF one is green VRF and another is blue VRF. [boxads] Virtual Routing and Forwarding basics (VRF) Diagram: Now one question what is VRF ? VRF associates to one or more interfaces on PE. Privatize an interface. [i.e. coloring of the interface in diagram] Has its own routing table and forwarding table (CEF) VRF has its own instance for …

by ShahedSeptember 1, 2011October 24, 20150

MPLS VPN Connectivity diagram: Today i will discuss about MPLS VPN Connectivity diagram or how a MPLS VPN domain buildup in service provider environment. [boxads] MPLS VPN domain are consist mainly P & PE router. P router means provider router, and PE router means provider edge router. P router are only forwarded Level & PE router collect & distribute customer prefixes. If we look bellow diagram we see P & PE router how connected. MPLS VPN Connectivity diagram:

by ShahedAugust 26, 2011October 22, 20150

BGP Regular Expressions Cheat Sheet Regular expressions are strings of special characters that can be used to search and find character patterns. Within the scope of BGP in Cisco IOS regular expressions can be used in show commands and AS-Path access-lists to match BGP prefixes based on the information contained in their AS-Path. [boxads] In order to understand how to build regular expressions we first need to know what the character definitions are for the regex function of IOS. The below table illustrates the regex characters and their usage. This information is contained in the Cisco IOS documentation under the …

by ShahedAugust 1, 2011October 22, 20150

BGP Best Path Selection Algorithm Cisco router BGP is the protocol used to announce prefixes throughout the internet. It’s a very robust protocol, and very useful to carry lot of prefixes, such as the Internet prefixes or internal client prefixes of an ISP. BGP Best Path Selection Algorithm Cisco router when a prefix is received in BGP, the path passes through two steps before being chosen as candidate to populate the RIB.[boxads] The first step consists on checking if the path is valid. If it is, the prefix will get into the BGP table, and later the second step of …

by ShahedJuly 27, 2011October 22, 20150

BGP MED Attribute Configuration example BGP MED Attribute Configuration example BGP MED is an optional non-transitive attribute meaning its not propagated throughout the whole internet but just to adjacent AS. The word “optional” means that this is not necessarily by default sent with the BGP updates. The purpose of MED is to influence how other autonomous systems enter your AS to reach a certain prefix. If the other attributes are set to default, MED will be the attribute used for path selection however, if Weight or Local preference is configured on the adjacent AS router, then MED will not be …

by ShahedJuly 24, 2011October 22, 20150

Removing Private AS Numbers in BGP Autonomous System (AS) is identified by a number in the range 1 to 65535. AS numbers in the range 1 to 64511 are assigned by InterNIC. These are reserved and globally unique AS numbers. AS numbers in the range 64512 to 65535 are known as private AS numbers, and like private IP addresses, these can be used to address ASs when a globally unique AS number is not necessary. It is important to ensure that the private AS numbers are not introduced into the global BGP table through the AS-Path attribute. To removing private …