Multi-homing Overview

The technological advancement that resulted in the establishment of Internet communication has impact on all aspects of working life. The need for reliable and redundant internet connectivity on the end user side has resulted in such a technique called “Multi-homing”which is a configuration of several network interfaces/IP addresses in customer premise equipment. A single network channel has proved to be less advantageous than the multiple connections. This is because multiple connections work based on different network segments thereby proving to be more reliability than the single network channel. Multiple network connectivity depends on various service providers available at your location. A host that holds multiple IP addresses and has physical connectivity to multiple data networks is called a Multi-homed server or a Multi-homed computer, this act like a router or gateway device.

Following are the various scenarios or variants of Multi-homing:

Single Link – Multiple IP addresses
Multiple Interfaces – An IP address per interface
Multiple Links – An IP address
Multiple Links – Multiple IP addresses

Similar to multihoming technique is Dual homing, a network topology that connects two devices to the network. It provides two independent access points, first is the primary connection, and second is the standby connection that activates in case of primary connection failure.

Protocols that supports Multi-homing

Border Gateway Protocol (BGP) is an exterior routing protocol that can exchange routing information across the Internet. A Multi-homed network that runs BGP can ensure network uptime by providing various routes in and out of the network for traffic flow. If a customer is in need of multi-homed service, the Internet service providers make use of BGP to set up routing between one another. BGP can efficiently perform functions such as network capacity, redundancy, network optimization, etc. Without BGP, expensive and higher capacity links might remain idle.

Configuring BGP is a cumbersome process and it requires knowledge of BGP programming. When technical support engineers configure BGP, they require AS number (Autonomous System number), range of IP addresses, prefixes, netmask notations, address allocation, and assignment policies. They have to plan physical infrastructure, the number of routers required, connections in the setup, bandwidth requirement from ISP, and so on. Hardware should have enough CPU capacity and memory to support BGP. Engineers can configure BGP and direct filters to ignore improper route announcements. Routing policy has to be registered in Routing Registry. They have to check frequently one by one whether all destinations can be reached. An expert in BGP programming can fine-tune the BGP properties to balance the traffic with available bandwidth. BGP and multi-homing configuration can meet Internet performance, reliability, and redundancy goals in a cost-effective manner.

Stream Control Transmission Protocol (SCTP) is similar to or provides some of the same features of Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). Multi-homing makes use of single SCTP endpoint to connect two or more IP addresses. By this, multi-homing can guarantee stability of connection associated with the host. When redundancy is critical, SCTP multi-homing proves to be advantageous. It ensures reliability by providing facilities such as Multi-streaming and Multi-homing to control the congestion in transport of messages. Moreover, it supports multi-homed network by facilitating transparent fail-over between redundant network paths.

When an enterprise network connects multiple service providers at the same time, it is called Site Multi-homing. SHIM6 (Site Multi-homing by IPv6 Intermediation) is a layer protocol that provides IPv6 multi-homing with failover and load sharing. A site host makes use of SHIM6 protocol to setup peer hosts, for this, the network has multiple provider allocated IPv6 prefixes. The advancement of technology has given birth to IPv6, the next generation Internet Layer Protocol for packet switched internet-works used in multi-homing. IPv6 provides resilience against failure of links, hardware, or protocols in the network. It provides network advantages such as redundancy, load sharing, transport layer survivability, DNS compatibility, traffic balancing across multiple providers, maintaining existing TCP and UDP sessions through cut-overs, etc.

Multi-homing Router

This device is specifically designed to handle multiple WAN connections or Internet links to provide link redundancy, bandwidth aggregation using bonding and load balancing through connection sharing methods.

Features of multi-homing router:

Load Balancing - Multiple connections for internet can be taken via cable, Broadband modem, satellite, etc to server load balancing in multi-homing. When multi-homing is set up using specialized link load balancer or WAN load balancer in between link routers and firewall, it detects saturation and failure of links and redirects traffic. Load balancing and failover can be handled without BGP routing tables. For this purpose, WAN link controllers make use of Network Address Translation (NAT) that unifies incoming and outgoing traffic to various destination IP addresses.
Link Redundancy – A multi-homing router provides high availability through link redundancy by protecting against failure of physical links. For link redundancy, two interfaces are taken for the router, they are assigned IP network for each, and a routing protocol interacts with connected routers for link selection.

Multi-WAN Router

To increase the business performance, the corporate network is radically focusing on designing a WAN infrastructure with fundamental WAN design goals. Two or multiple WAN connections for a network have become adequate to ensure redundancy, fault-tolerance, fail-over capability, etc. Multi-WAN router, a component of WAN infrastructure, is a device that forwards data packets from a network to another using multiple WAN connections.

In addition to essential requirements like higher performance and throughput, customers require more features from a Multi-WAN router. It should support multiple WAN ports, outbound load balancing by session, weight round robin, etc. It must assure Quality of Service (QoS) and send alerts through email in case of emergency. In addition to this, few features of the Multi-WAN router are discussed below:

Internet Sharing – Router should be able to support hundreds of users sharing multiple WAN lines.
DHCP – Dynamic Host Configuration Protocol Server configures IP address for the computers in network, and provides netmask, gateway, and DNS addresses automatically.
NAT - Network Address Translation helps the router to share the Internet connection among all the systems connected to the local network.
DMZ Host – A router that supports multiple DMZ host can easily forward all ports to other firewall or NAT device.
Data Logging System – This system should record WAN failures, restores and other information with time and date. This is an easy way to diagnose problems in the activity of the system.
SPI firewall – A Multi WAN router with State Packet Inspection firewall inspects the state of packets and examines the header and footer. It ensures security to incoming traffic.
DNS – Multi-WAN router should allow separate DNS entries for EACH WAN.
User-friendly GUI – Router should have easy-to-use user interface for configuration and management.

A Multi WAN router with above features can ensure high performance for multiple WAN connections. In precise, it can increase the network speed and provide less downtime.

Benefits and Advantages of Multi-homing

Bandwidth Aggregation – Multi-homing is cost effective solution for an organization that requires more bandwidth. It bundles multiple connections to provide combined bandwidth to the network.
Increased Reliability – Since multiple connections are used, if one connection becomes unavailable then others can takeover. Moreover, reliability is assured when multi-homing techniques route Internet sessions from congested links.
Load balancing in Multi-homing increases throughput, and diverts traffic from non-functional links in case of failure. In addition, it lowers the number of systems connecting to Internet through single connection.
Less downtime - Multi-homed network assures redundancy indicating less downtime during failure. It supports add-on like WAN link controllers to maintain the network connectivity in case of natural disasters or adverse events that extents for a period of time. Consequently, multi-homing is part of Disaster Recovery Initiatives and Business Continuity Planning.
WAN redundancy - WAN Redundancy is must for a backup system in a network; this ensures continuous uptime and flow in case of business continuity. A greater WAN redundancy is assured when an organization multi-homes their sites with two or more WAN links from different ISP’s.