1. Overview/Introduction
This document is meant to concisely describe the signalling options that Deutsche Telekom's AS3320 makes available to customer networks supported by BGP routing (transit service products). The intended audience is a customer's network administrator who is familiar with BGP and general public Internet routing techniques as well as how to configure and control their routers. This version of the document describes the options as defined for the initial roll out of the advanced routing policy definitions (implemented using the TROPOS configuration generator) identified as TSD3320 v1.0 targetted for January 17th 2005.

Verizon Business supports a user configurable routing policy by allowing customers to fine tune their routing announcements via the BGP community attribute. The following information outlines the policy and demonstrates how customers can implement the routing policy of their choice.

Cogent will send the customer a complete BGP table without aggregating the internal Cogent routes. This is useful for customers who are multi-homed within the Cogent Network.

1. SAVVIS Received BGP Community Attribute Values (BGP community String)

SAVVIS Prepend/Suppression BGP Community Attribute Values (3561:30PPN)

SAVVIS allows customers to control certain traffic flows off-net with the implementation of BGP community attribute values that prepend route/prefix paths with additional AS hops. These BGP community attribute values, which the customer applies, affects the way SAVVIS peers choose the degree of preference of a given prefix/route, because the number of AS hops within the route-path has been lengthened.

Level 3 BGP Communities 

Level 3 (AS3356) does not allow any part of 4.0.0.0/8 to be multihomed. If you are a customer who is currently using address space from 4.0.0.0/8 and if you need to multihome your network to another provider, please contact Level 3 for new address space which can be multihomed.

Global Crossing (GBLX) allows customer to control their routes announced within GBLX/AS3549 network using bgp community string. These community strings can be used various attributes of their prefixes announced within GBLX network, and can be useful if you are multihomed with another IP transit.

Global Crossing has standard policy applied for its customers and peers.

Customers:

Local preference : 300

Metric policy : Accept customer's metric

BGP community attribute is such a way for tagging routes.  It is widely used for route manipulating.  Administrator can tag a community to a route then set a policy when the community is match.  BGP community can be used to influence routes at the upstream, so it affect the way routes back to our network or inbound traffic.

Configuring RIP for routing protocol between PE and CPE on MPLS VPN cover three steps.
1. Configure RIP on CPE
2. Configure RIP on address-family level on MPLS PE
3. Redistribute RIP to BGP vice versa on MPLS PE

Sample BGP regular expressions that can be used on Cisco router.
_100_ Going through AS 100
^100$ Directly connected to AS 100
_100$ Originated in AS 100
^100. Networks behind AS 100
^[0-9]+$ AS paths one AS long
^([0-9]+)(_\1)*$ Networks originating in neighboring AS
^$ Networks originated in local AS
.* Matches everything

BGP route selection criteria (on Cisco router) :

1. Exclude route with inaccessible next-hop
2. Prefer highest weight (local to router)
3. Prefer highest local preference (globa within AS)
4. Prefer routes that router originated
5. Prefer shortest AS paths (only length is compared)
6. Prefer lowest origin code (IGP
7. Prefer lowest MED
8. Prefer external (EBGP) path over internal (IBGP)
9. For IBGP paths, prefer path through closest IGP neighbor
10. For EBGP paths, prefer oldest (most stable) path
11. Prefer paths from router with the lowest BGP router-id

Before configuring BGP, you need gather information about your network and peer. Basically, configuring BGP on Juniper router is the same with Cisco or another router. Basic configuration is just configure BGP session the advertise our network.

Configuring BGP on Cisco router is simple enough. Before start configuring BGP, you need two consideration :
1. BGP only advertise routing entry that exist in IGP routing table
2. BGP is classfull routing protocol, you must include netmask in network statement BGP configuration if the network is not classfull.

IT is important thing in business today. Many company have IT consolidated or centralized, meaning that application or data center is centralized at head quarter or centralized data center. This scenario include file server consolidation, email consolidation, and application consolidation. File server consolidation reduces complexity, increases efficiency, and reduces risk. Email consolidation simplifies management and upgrades matter.