Re: Can a prefix be never routed on Internet but used only for source address in IP packets?
This happens unintentionally quite a bit with misconfigured NAT. You will see RFC 1918 source addresses in packets from time to time. I can't speak to the application or value of this, but I have seen this and done it accidentally on one occasion. Jonathan Kalbfeld office: +1 310 317 7933 fax: +1 310 317 7901 home: +1 310 317 7909 mobile: +1 310 227 1662 ThoughtWave Technologies, Inc. Studio City, CA 91604 https://thoughtwave.com View our network at https://bgp.he.net/AS54380 +1 844 42-LINUX
On Aug 19, 2025 at 9:34 AM, Sriram, Kotikalapudi (Fed) via NANOG <nanog@lists.nanog.org> wrote:
Question: Can a prefix be never routed on the Internet but used only one-way for source address in IP packets?
That is. a user owns an IP prefix. They never advertise a route to it in BGP on the Internet. But they use the prefix solely for source address in IP traffic from a source to a destination (sink). In this set up, the destination server obviously cannot/doesn't return any acknowledgements etc. to the source. Anyone aware if there is any such known application in use on the Internet - even if it is rare? Thanks.
Sriram _______________________________________________ NANOG mailing list https://lists.nanog.org/archives/list/nanog@lists.nanog.org/message/MSEGDFSZ...
I think that’s the nature of unidirectional ip flow. Unless source-based PBR, FBF, or uRPF (iirc, strict) is in use, seems that’s how regular IP works in a unidirectional manner Aaron
On Aug 19, 2025, at 11:37 AM, Jonathan Kalbfeld via NANOG <nanog@lists.nanog.org> wrote:
This happens unintentionally quite a bit with misconfigured NAT. You will see RFC 1918 source addresses in packets from time to time. I can't speak to the application or value of this, but I have seen this and done it accidentally on one occasion.
Jonathan Kalbfeld
office: +1 310 317 7933 fax: +1 310 317 7901 home: +1 310 317 7909 mobile: +1 310 227 1662
ThoughtWave Technologies, Inc. Studio City, CA 91604
View our network at
+1 844 42-LINUX
On Aug 19, 2025 at 9:34 AM, Sriram, Kotikalapudi (Fed) via NANOG <nanog@lists.nanog.org> wrote:
Question: Can a prefix be never routed on the Internet but used only one-way for source address in IP packets?
That is. a user owns an IP prefix. They never advertise a route to it in BGP on the Internet. But they use the prefix solely for source address in IP traffic from a source to a destination (sink). In this set up, the destination server obviously cannot/doesn't return any acknowledgements etc. to the source. Anyone aware if there is any such known application in use on the Internet - even if it is rare? Thanks.
Sriram _______________________________________________ NANOG mailing list https://lists.nanog.org/archives/list/nanog@lists.nanog.org/message/MSEGDFSZ...
_______________________________________________ NANOG mailing list https://lists.nanog.org/archives/list/nanog@lists.nanog.org/message/POV2RZVC...
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