My question is maybe sort of awkward. Is our local Internet exchange using public IP addresses for communicating with other branches, and if they are, then suppose my PTCL (ISP) Lahore exchange public IP address is, then what should be the IP address of the Islambad Internet exchange? Is it something like 182.191.226.X, or there is a backup public IP address use by another exchange, and if they are using different IP addresses because my friend public of ISP exchange is, then how do the two branches communicate with different public IP addresses under the same infrastructure of PTCL?

It would be very helpful for me to understand this concept.

  • Could you explain what PTCL is?
    – user36472
    Commented Aug 14, 2017 at 12:09
  • Ptcl is an ISP.
    – CrackTechs
    Commented Aug 14, 2017 at 12:15

1 Answer 1


Each site should have a different public address. A problem would be if the different sites had the same IP address.

Your ISP can have many different networks assigned by the RIR, and customers can be assigned addresses from any of the networks. Routers route traffic between networks, and your ISP will have a bunch of routers that do just that. Traffic from one of your ISP networks will be routed to and from your other ISP networks, and even other ISPs. That is what the Internet is.

Unfortunately, we cannot explain how your ISP network is connected internally. You would need to discuss that with the ISP, but it is likely that it will not reveal that information. Every ISP does things differently, and each will want to keep its internal network structure proprietary.

  • Suppose my ISP has its three further branches in different cities every city contain 3 lacks users by letting it like this that every user contain a single public Ip address ,in that case of three cities it become 9 lacs so Is my ISP bought 9 lack public Ip from IANA !
    – CrackTechs
    Commented Aug 14, 2017 at 12:38
  • It is impossible for us to determine what your ISP does internally. It could have one network across multiple cities, it could have multiple networks in one city, etc. Also, understand that networks are determined by the length of the network mask, not the octets, which are just for human readability and have nothing to do with how a network is divided. The RIRs assign the networks to the ISPs, IANA assigns them to the RIRs. IANA has run out of IPv4 networks for several years, and the RIRs have run out of IPv4 networks to assign to the ISPs. The networks are assigned in different sizes.
    – Ron Maupin
    Commented Aug 14, 2017 at 13:04

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