I had some headache with a proxy setup which I couldn't figure out. Turns out that only "" and "localhost" were recognized as "localhost" or "internal" IP addresses, whereas (my router) had to be manually added to a list of "do not use proxy for".

But isn't "192.168." always internal/local? Isn't it one of those weird "special ranges"? Can they ever refer to an external/outside machine? Why would not that, and the other "special ranges", always be ignoring any proxy configuration?

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    That range is "private" not "internal." And how would you define internal anyway? On my customer's network, there are 192.168. networks hundreds of miles away from others. – Ron Trunk Oct 8 '20 at 17:03
  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can post and accept your own answer. – Ron Maupin Dec 17 '20 at 22:41

The range is a Private IPv4 address range as defined by RFC 1918, Address Allocation for Private Internets, but that does not mean it is defined as "internal." It means that the ISPs have agreed to not route packets with those addresses on the public Internet, but that does not mean that IPv4 distinguishes Private addresses from any other addresses. IPv4, itself, does not have the conept of Private and Public addresses.

If you look at the IANA IPv4 Special-Purpose Address Registry, it explains the special address blocks that are recognized by IPv4, and those that are not. For example, the block is Reserved-by-Protocol* (recognized by IPv4), but any of the Private address blocks are not.

You seem to be forgetting that a lot of businesses have multiple routers internal to the business, and having a router demand that all Private addresses be recognized as "internal" and not routed would be a real problem. Addresses that are not reserved by the IPv4 protocol rightly need special configuration for special handling by a device because, as far as the device is concerned, they are simply IPv4 addresses.

*Reserved-by-Protocol - A boolean value indicating whether the special-purpose address block is reserved by IP, itself. This value is "TRUE" if the RFC that created the special-purpose address block requires all compliant IP implementations to behave in a special way when processing packets either to or from addresses contained by the address block.


The RFC 1918 IP address ranges are marked as private, meaning they can't and mustn't be used on the open Internet. What you do with those addresses within your (private) network is entirely up to you.

A proxy doesn't have an inherent logic to decide whether it's required or not. Actually, it's the source node ("client") that decides whether to use a proxy for the destination or not, and the source can't make the decision without proper configuration.

There are quite a few scenarios where a proxy is (at least somewhat) reasonable within a private network, so yes, you do need to configure all address ranges that the proxy is not used for, even private addresses. Conversely, there are several scenarios where you'd want to connect from private to public IP space without a proxy or source NAT (e.g. into a public-address DMZ).

Whether proxy or SNAT - "always proxy/source NAT from private to non-private" isn't a bright idea. It covers 98% of the scenarios but miserably fails for the last 2%. It's much more reasonable to actively configure what you actually require.

  • This also applies to your ISP or carrier's in-house networks, leaving your phone behind CGNAT. Note also that some enterprises also re-use obscure ranges of public internet addresses on their private networks and rely on the "real" owners not being important. – mckenzm Oct 9 '20 at 1:31
  • IP address 192.168 .88.1 is private ip address range .but it's depends upon your requirement whether to define it's as internal or not .. ISP won't route this ip address ranges but still check your ISP sometimes service providers will use private ip ranges for routing between ISP edge router and your organization edge router. – Sagar Uragonda Oct 9 '20 at 3:21
  • I was trying to point out legitimate uses of RFC1918 addressing... ;-) – Zac67 Oct 9 '20 at 6:29

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