Martian and RFC1918 addresses

Daniel Senie dts at
Thu Jul 29 23:57:24 UTC 1999

rfuller at wrote:
> I have been reading Cisco's "Essential IOS Features Every ISP Should
> Consider" document and came across a section called Martian and RFC1918
> networks.  It is discussing different bogus or reserved networks that
> should be filtered by every ISP.  In the list are some addresses I thought
> were legal and after checking the ARIN Whois database, some of them seem to
> be.  Can anyone give me some additional information as to the need to
> filter the following networks:

Some of these are indeed questionable. I recommend using Bill Manning's
draft on this subject (draft-manning-dsua-01.txt) as a guide, rather
than Cisco's document. Page 27 of Cisco's document has a sample
access-list which does match Bill's document. Page 59 of the document
has the list you saw and were concerned about. It claims the information
comes from the NANOG list. Hmmm...

>             reserved for IANA
>          this belongs to Ford
>            reserved for IANA
>         this belongs to SUN

>         IANA use for local link numbers???

169.254/16 should never be routed. It's used for self assigned
addresses, and is useful in small networks especially. Win98 takes
advantage of this if DHCP fails to find a server. It allows a small
cluster of systems to select unique IP addresses, and in the case of
Windows, they'll then talk Netbios over IP on that. It eliminates the
need to use Netbeui, which in itself is a good thing.

>      reserved for IANA

192.0.2/24 is set aside for use in documentation and examples. By
ensuring this block is not routed, folks who type the exact values from
their documentation don't screw up someone else's network.

>      no ARIN match
>         no ARIN match
>          this belongs to SUN
> If you can elaborate on what they are used for and if any problems would
> arise from filtering these networks, it would be appreciated.  If you could
> also please include where you found the information, I would appreciate it.
> Some of them belong to companies, so why would you filter them?  Are they
> development networks for Ford and SUN?  Are there any other martian
> networks that should be filtered?

Lots of folks used to set up their Sun workstations on private networks
using Sun's IP space, 'cause that's what was in the Sun documentation.
The only thing I can figure is the other blocks in the example must be
ones that were frequently used in documentation and got used in a lot of
private networks that later connected to the public network. Anyone have
better insight into these?

Daniel Senie                                        dts at
Amaranth Networks Inc.  

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