Routing Protocol Solution

Routing Protocol Solution Should Be Based On Individual Network Requirements, But Should Be Limited To Static Routes, RIP V2, OSPF, EIGRP, IS-IS And BGP Routing Protocols

Building multi-sites network environment that separates each other across different city, different state, or even different continental / geography, the need of well-managed inter-network fast-convergence routing information is a must.

Routing is the process of performing intelligent path selection in the delivery of data across an internetwork. Choice of path can be influenced by the use of static routes, dynamically with an intelligent routing protocol or a combination of both. Dynamic routing protocols can be used to automatically exchange network path information between routers. This is important in large complex networks where potentially many paths may exist to a remote destination.

For organization that contains multiple sites / remote sites, the routing connectivity should be based on individual network requirements, but should be limited to static routes, RIP Version 2, OSPF, EIGRP, IS-IS and BGP routing protocols.

The Open Shortest Path First (OSPF) however must be used to provide connectivity to the corporate WAN core (backbone).

The minimum requirement with regards to Routing Protocols is:

• Static (and default) routes may be used to provide internetwork connectivity.
• The OSPF (version 2) routing protocol is to be used for the connection to the corporate WAN core.
• Internal (within the sites) routing protocols are limited to RIP version 2, OSPF, IS-IS and EIGRP. RIP version 1 should not be used.
• BGP may be used for multi-homed Internet connections or multi-business unit interconnections.

The following provides background information regarding routing protocols:

Static routes are recommended for small hub and spoke style networks or networks that lack sufficient bandwidth to periodically advertise route tables. Static routes (with default routes) are often the easiest way to connect remote sites to a major central site.

Dynamic routing protocols are commonly used in complex environments and/or when networks undergo topology changes that require them to converge quickly. The key characteristics of any routing protocol include;

• Routing overhead (router memory and network bandwidth),
• path selection process (metric),
• convergence time,
• Scalability and support for advanced features such as route summarization and Variable Length Subnet Masking (VLSM).

Many routing protocols exist including:

• RIP (version 1 and 2), (RFC 2453, 1721)
• OSPF, (RFC 2328)
• IS-IS, (RFC 1195)
• Cisco’s IGRP and EIGRP, EIGRP (Enhanced IGRP) is a Cisco proprietary routing protocol only suitable for running on Cisco IOS routers
• BGP (RFC 1771).

However due to a network stability and functionality reasons only RIP Version 2, OSPF, IS-IS EIGRP and BGP should be used within the corporate environment.

In a large organization, networks should be planned to ensure effective IP addressing through the use of subnets and route summarization. Route summarization can be used to greatly reduce the impact of advertising large network tables. Route summarization is also an effective way of reducing the memory and processing requirements of all routers in a large enterprise network.

The following information can be used to assist with routing protocol selection:

RIP (Routing Information Protocol) is a popular distance vector routing protocol designed for small usually hub and spoke networks. It sends periodic updates every 30 seconds and uses a hop count (number of routers) as its path selection process (metric). This can generate excessive overhead on low bandwidth links. There are two current versions of RIP, namely RIP v1 and RIP v2. RIP v2 has some enhancements over v1 including Variable Length Subnet Masking (VLSM) and support for route authentication.

OSPF (Open Shortest Path First) is a popular standards based link-state routing protocol. It uses multicast to transmit incremental network updates and is thus very fast to converge with little impact on the network. It supports VLSM and manual route summarization, and uses a bandwidth based cost as it’s metric. OSPF requires a hierarchical design and does have a number of topology constraints that must be followed.

IS-IS (Intermediate System – Intermediate System) is a less popular OSI standards based protocol similar in fashion to OSPF. EIGRP (Enhanced Interior Gateway Routing Protocol) is a popular hybrid (advanced distance vector) routing protocol developed by Cisco Systems. It offers fast convergence, VLSM, low network/router overhead and is backward compatible with earlier IGRP implementations. It uses a composite metric consisting of a bandwidth and interface delay function. It supports symmetric and asymmetric load balancing as well as supporting both automatic and manual route summarization on any network interface boundary. See also IP routing guide

BGP (Border Gateway Protocol) is an exterior (advanced distance vector) routing protocol used between large autonomous networks to exchange Internet routes. The use of BGP should be avoided unless a multi-homed Internet connection (or complex multi-organization peering) is required, and the use of a BGP routing policy is well understood.

The choice of routing protocol has a number of significant implications including scalability, convergence and path selection. If implementing a high availability based solution a routing protocol with rapid convergence must be chosen (typically OSPF or EIGRP). Carefully planning and needs analysis of specific routing requirements must be undertaken to ensure reliable routing connectivity exists within the network.

For company tele-workers that frequently travel for business, the need of remote connection to corporate network becomes the need to support their mobile activity. The use of standard tunneling with secure L2TP/IPSec should be use to connect to the corporate network via public network.

Reference: Cisco

See also:

• networking security essentials
• home firewall – the basic concept
• computer networking diagram