Not announcing (to the greater internet) loopbacks/PTP/infra - how ?

Karl Gerhard karl_gerh at
Thu Oct 4 19:59:44 UTC 2018

Hello Brandon,

instead of not announcing it you can send it to your upstream and tag it with no-export.
That way you can still see your router in traceroutes if the source ASN of the traceroute doesn't do uRPF.

If you don't have a separate range from which you assign PTP/loopback addresses, but your upstream offers a BGP blackhole community you can permanently blackhole your PTPs/loopbacks/infra at your upstream if you want to increase your security. Another way to keep your traceroutes pretty. However, if it's thousands of /32s then you should probably talk to your upstream before doing that. :)


*From:* Brandon Applegate [mailto:brandon at]
*Sent:* Thu, Oct 4, 2018 9:07 PM CEST
*To:* NANOG mailing list
*Subject:* Not announcing (to the greater internet) loopbacks/PTP/infra - how ?

> Hello,
> I’ve seen mention on this list and other places about keeping one’s PTPs / loopbacks out of routing tables for security reasons.  Totally get this and am on board with it.  What I don’t get - is how.  I’m going to list some of my ideas below and the pros/cons/problems (that I can think of at least) for them.
> - RFC 1918 for loopbacks and PTP
>   - Immediately “protects” from the internet at large, as they aren’t routable.
>   - Traceroutes are miserable.
> - Use public block that is allocated to you (i.e. PI) - but not announced.
>   - So would this be a totally separate (from user/customer prefixes) announcement and allocation ?  In other words, let’s say you were a small ISP getting started.  You manage to get a /20 from a broker (IPv6 should be “easy”).  Do you also now go out and get a /23 (I’m making these sizes up, obviously all of these will vary based on ISP size, growth plan, etc.).  You have the /23 registered to you (with proper rDNS delegation, WHOIS, etc.).  But you simply don’t announce it ? I’d say I need this /23 day one to even build my network before it’s ready for customers.
>   - On the IPv6 front - would a RIR give you your /32 and then also a /48 (for loop/PTP) ?
> - Deaggregate and not announce your infra
>   - Bad net behavior out of the gate with this method.  The opposite of elegant.
>   - Keeping with previously made up / arbitrary prefixes - for your /20 - you’d end up announcing 2 x /23, 1 x /22 and 1 x /21.  I’m too lazy to enumerate the IPv6 gymnastics, but with IPv6 you could “waste” a bit more to get to boundaries that are a bit easier to work with I suppose.
> Thanks in advance for insights on this.
> --
> Brandon Applegate - CCIE 10273
> PGP Key fingerprint:
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> "For thousands of years men dreamed of pacts with demons.
> Only now are such things possible."

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