Consequences of BGP Peering with Private Addresses

Jeff Wheeler jsw at
Thu Jun 16 11:09:04 UTC 2011

On Wed, Jun 15, 2011 at 12:47 PM, James Grace <james at> wrote:
> So we're running out of peering space in our /24 and we were considering using private /30's for new peerings.  Are there any horrific consequences to picking up this practice?

I agree with other posters that this is not a good practice.  Is it
somehow not possible for you to obtain additional address space?  Can
you not use neighbor-assigned /30s more frequently to avoid exhausting
your existing allocation?

For eBGP neighbors, I would sooner use non-unique /30s than utilize
RFC1918 space.  While this would not allow for correct reverse DNS,
and traceroute would be less obvious, it has fewer disadvantages than
assigning RFC1918 for your peer link-nets.  You will need to re-write
next-hop towards iBGP neighbors, though (using next-hop-self or
translating to internal numbers for routing protocol use) and you
should not re-use the same /30 twice on the same ASBR.

This may sound crazy, and it is certainly not an ideal way of doing
things; but it is an alternative worth consideration as networks
exhaust their available IPv4.

Jeff S Wheeler <jsw at>
Sr Network Operator  /  Innovative Network Concepts

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