2-3 ISP’s Internet – Multi Homing Scenario

Pain Area and aspects to be considered:-

  • Which type of Internet connectivity should take?
  • How can customer achieve 99.999% uptime for Internet connectivity?
  • Who will provide the IP block (subnet)?
  • Will it be a cost effective solution?
  • What would be the default-gateway IP address of LAN users?
  • What happen if ISP1 Internet connectivity goes down?
  • Can customer get their OWN IP block for advertisement?
  • How many ports required to connecting Internet connections on CPE?

Internet – Multi-Homing – Solution Proposed

In Today’s world everybody knows what is Internet and what are benefits and advantages of the Internet connectivity, so some of the customer can’t afford any kind of down time from any services provider for any xyz reasons. Basically it totally depends upon the criticality of the business, as some of businesses can afford downtime or some cannot afford even a single minute down time.

First of all customer should prefer Teristrial last mile connectivity as it is more reliable/scalable source of last mile in comparison to RF or any other last mile. Best way to achieve 99.9999% uptime is to have 2 separate Internet connectivity from 2 different ISP’s because if in any case ISP-1 goes down traffic would be rerouted through ISP-2. This scenario called Multi-Homing scenario where 2 different ISP’s terminates at Customer’s end.Customers have to make sure that both the Service providers should not offer same last connectivity at that location unless if any last goes down that site would be isolated because both the last miles are same, so one link should be on Teristrial last mile and other would be on RF or use other service provider last mile connectivity to ensure better uptime.

To implement this scenario into existing network customer should have taken own Public IP’s block + AS no from APNIC because customer can’t configure 2 separate Public IP Subnet into their network. Once customer receive OWN IP Subnet + AS no from APNIC, next step is to run BGP as routing protocol between CPE to both the ISP’s CE with BGP attributes which decide outgoing path/incoming path and advertise own IP subnet to both the service provider so that Customer’s IP Subnet would be reachable to outside world from both the ISP’s. Configure i-BGP between both the CPE’s at customer end for redundancy and at LAN side HSRP/VRRP should be enabled. Router should feature to support BGP routing protocol and should have required minimum ports (1 Routed port + 1 LAN port) to terminate Internet connection.


2 ISP's Internet - 2 CPE



Technical Arrangement’s:-

  1. Terminate both ISP’s Internet Links on different CPE’s for redundancy.
  2. NATTING OR PATTING configuration is required to route Private LAN IP Pool on Internet cloud.
  3. Router should have minimum 1 Layer3 port + 1 Layer2 port CE.
  4. Configure i-BGP between both the CPE’s along VRRP/HSRP on LAN side for redundancy.
  5. Default gateway IP address of LAN devices will be virtual IP address of VRRP/HSRP.
  6. Configured eBGP between CE-PE with BGP attributes. (Weight and Local Preference for Outgoing traffic and AS Prepend for incoming traffic).
  7. Advertise OWN IP subnet to both the ISP’s.


Akshay Sharma

AKshay has a rich experience of 10+ years in data and telecom domains. He is working as a solution architect in a reputed Telecom in India from the last 5 yrs and has diversified experience in providing robust network solution to SMB and enterprise segment. His core expertise is in DSL broadband/IP/MPLS/Routing and switching with hands on multiple telecom equipment’s and had done multiple certifications into his long career.

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1 Response

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