Multiple Internet locations with same subnet

Pain Area and aspects for consideration:-

  • Which type of Internet connectivity should take?
  • How can customer achieve 99.999% uptime for Mission Critical Applications?
  • Who will provide the IP block (subnet)?
  • Will it be a cost effective solution?
  • Can customer get same IP block from single ISP at all the different locations?
  • What happen will if any location Internet connectivity goes down?
  • How many ports required to connecting Internet connections on CPE?

Multiple Internet locations with same subnet

Since Internet is one of useful resource for any organization for communication, every customer expected less downtime and better services from ISP. Since this is fastest medium of communication hence all the companies are deploying Internet as connectivity to grow their network.

Today’s technology supports Internet over various platforms like Broadband, Internet over Leased Line and over Mobile network. This is detail scenario where customer has Internet connectivity from Single Service Provider at his number of different locations and wanted to use same subnet from the corresponding ISP at all the locations for high availability or those customer who runs mission critical sites on Internet platform of their DC-DR scenario.

 One way to have OWN set of IP’s from APNIC and advertise to corresponding ISP through BGP but 2 major challenges are 1st it is costly solution and 2nd time taking procedure to apply in APNIC and get the IP block on time.

Simplest way to resolve this problem is to have same subnet of IP’s from the ISP and configure at both the locations. Customer should have any Router which supports BGP protocol at least with required number of ports (1 Routed port + 1 Layer2 port). Customer will run eBGP with Private AS number with the corresponding ISP and use BGP attribute (As path prepend) at one of location or advise ISP to configure Local preference attribute at their end for any one of customer location. After this configuration, IP Subnet will be reachable through ISP to the rest of world but if any location Internet goes down IP subnet would be still reachable through another path and uses would get seamless connectivity without any fail.     


Case Study – 2 Internet locations with same subnet


Technical Arrangement:-

  1. Internet Links should be terminated on different CE routers from same ISP.
  2. Recommended routing protocol is eBGP between CE-PE.
  3. Configured same IP block provided by ISP on different location.
  4. Configure eBGP with private AS no along with BGP attribute AS path prepend on CE Router.
  5. Else advice ISP to configure eBGP along with BGP attributes Local preference on PE Router.
  6. Routers should have minimum 1 Layer3 port + 1 Layer2 port at both the locations.
  7. Router should support BGP as routing protocol.


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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