[ppml] Policy Proposal 2006-2: Micro-allocations for Internal infrastructure - Last Call

Member Services info at arin.net
Fri Oct 13 14:31:18 EDT 2006

The ARIN Advisory Council (AC), acting under the provisions of the ARIN
Internet Resource Policy Evaluation Process (IRPEP), has reviewed Policy
Proposal 2006-2: Micro-allocations for Internal Infrastructure and has
determined that there is community consensus in favor of the proposal to
move it to last call. The AC made this determination at their meeting at
the conclusion of the ARIN Public Policy meeting on 12 October 2006. The
results of the AC meeting were reported by the Chair of the AC at the
member meeting. This report can be found at

The policy proposal text is provided below and is also available at

Comments are encouraged. All comments should be provided to
ppml at arin.net. This last call will expire at 23:59, Eastern Time, 27
October 2006.

The ARIN Internet Resource Policy Evaluation Process can be found at


Member Services
American Registry for Internet Numbers (ARIN)


Policy Proposal 2006-2: Micro-allocations for Internal Infrastructure

Policy statement

Proposal type: modify

Policy term: permanent

Policy statement:

6.10.1 Micro-allocations for Internal Infrastructure

Organizations that currently hold IPv6 allocations may apply for a
micro-allocation for internal infrastructure. Applicant must provide
technical justification indicating why a separate non-routed block is
required. Justification must include why a sub-allocation of currently
held IP space cannot be utilized. Internal infrastructure allocations
must be allocated from specific blocks reserved only for this purpose.

Policy Rationale

Organizations that have only a single aggregate may require additional
noncontiguous IP space for their internal infrastructure. This space
should not be routed in the global Internet routing table. This will
provide for the protection of internal infrastructure and support for
applications that are sensitive to long convergence times like VoIP.

It is important to note that the additional prefix allocation will not
negatively impact the global routing table size as the additional prefix
should not be routed.

BGP Re-Convergence

ISPs use BGP to originate their aggregate from multiple nodes within
their infrastructure. They do this by routing their aggregate to discard
on multiple devices. This ensures the Internet can reach the aggregate
even when one or more nodes fail.

If the next hop for a route is reachable via an aggregate that is in the
routing table, then failures affecting the reachability of the next hop
are subject to BGP hold timers, which can cause traffic to be dropped
for the length of the bgp hold time

(typically 3 minutes)

The BGP re-convergence problem results when a multi-homed customer is
announcing the same route to two different edge routers. When the edge
router sourcing the primary path fails, the local address which is
acting as the next hop, is removed from the IGP. If the next hop is
still reachable through an aggregate or covering route, then the route
will not be immediately invalidated in bgp. Until the bgp session with
the failed device times out, traffic will be drawn to the device
originating the aggregate, which is routed to discard and traffic will
be dropped. After the bgp session with the failed device times out, the
route will be removed and the next best route will be used. To minimize
route failover time, you must ensure that the local addresses of the
infrastructure, that act as next-hops for Internet routes, are NOT
numbered with addresses that are a more specific than the aggregate.

A detailed description of the problem space follows in the next three

Having BGP next-hops that are not aggregated can cause faster
convergence for customers who have multiple links to multiple routers of
a single upstream AS. Take the case where a customer has two
connections, link1 to edge-router1 and link2 to edge-router2, to a
single upstream AS. The customer has an eBGP session with the loopback
2001:DB8::1/128 on edge-router1 and with loopback 2001:DB8::2/128 on
edge-router2. The customer advertises a single prefix 2001:DB8:1000::/48
to both edge-router1 and edge-router2. The edge routers set next-hop
self. The upstream ISP will have two paths to the prefix
2001:DB8:1000::/48, one with a protocol next-hop of 2001:DB8::1 and one
with a protocol next-hop of 2001:DB8::2. Assume the upstream ISP's
entire network prefers the path to 2001:DB8:1000::/48 with a protocol
next-hop of 2001:DB8::1 due to lower BGP MED value. Also assume that all
of the address space owned by the upstream ISP is 2001:DB8::/32, and the
loopbacks of both edge routers are a more specific of the aggregate /32.
The upstream ISP has a pull-up route for 2001:DB8::/32 in the core of
the network. This allows for the aggregation of all the more specific
routes of 2001:DB8::/32. It insures the stability of the 2001:DB8::/32
announcement, while preventing an isolated edge router from advertising
reachability to the network.

If edge-router1 fails then 2001:DB8::1/128 will be immediately removed
from the IGP. The preferred prefix for 2001:DB8:1000::/48 with a
next-hop of 2001:DB8::1 will remain a valid bgp route and will continue
to be the best path because 2001:DB8::1 is reachable through the pull-up
route 2001:DB8::/32. Traffic will get blackholed for up to three minutes
(BGP default hold time) until the BGP prefix 2001:DB8:1000::/48 with a
protocol next-hop of 2001:DB8::1 times out. Only then will traffic get
forwarded to the next best path for 2001:DB8:1000::/48 with a protocol
next-hop of 2001:DB8::2.

If instead the loopbacks of the edge routers (or any BGP protocol
next-hop addresses) are not part of the 2001:DB8::/32 aggregate, and
there is no aggregate that covers the edge router loopbacks, then
convergence will be much quicker. Assume that edge-router1 is using
2001:408::1 and edge-router2 is using 2001:408::2, and the only pull-up
route is 2001:DB8::/32. In this case once edge-router1 fails, the IGP
will detect it and remove 2001:408::1/128 from the IGP. This will
invalidate the preferred path to 201:DB8:1000::/48 with a protocol
next-hop of 2001:408:1 as there will be no route to the next hop (or
even a less specific of this address). Once the path is invalidated,
then the next best path to 2001:DB8:1000::/48 with a protocol next-hop
of 2001:408::2 will be declared best. Convergence times will be on the
order of magnitude of the IGP failure detection and path re-calculation,
typically less than one second.

                       | Core Router |static route
                       |             |2001:DB8::/32 discard
                           |      |
                           /       \
            /-------------/         \--------\
           /                                  \
          /  /----------------------------\    \
          |  |                             |   |
------+---+--                         --+---+------
|Core Router|static route             |Core Router|static route
|           |2001:DB8::/32 discard    |           |2001:DB8::/32 discard
---------+---                         ---------+---
          |                                     |
---------+---------                   ---------+---------
|  edge-router1   |                   |  edge-router2   |
| 2001:DB8::1/128 |                   | 2001:DB8::2/128 |
---------+---------                   ---------+---------
          |                                     |
           \    link1                   link2   /
            \------------\            /---------/
                          \          /
                           |         |
                       |      CPE        |
                       |                 |
                      LAN 2001:DB8:1000::/48

Internal Infrastructure Security Considerations

Internal infrastructure could be numbered out of space that is not
routed or reachable by the public Internet. This could be used to secure
internal only services in a multi-layered approach by filtering direct
network connections in the forwarding plane, and not routing the network
in the global Internet routing table. Internal services which could take
advantage of these layers of protection include: SNMP services, iBGP
mesh, Out-of-Band management network(s), remote access to the network
devices that make up the network in question. A layered security
approach will help to prevent breaches in security via singular config
management problems. Additionally, having all of the services out of an
aggregate block will simplify the configuration management situation.

In essence, this allows for a two tier approach of protecting
infrastructure, both in the control plane by not routing the network,
and in the forwarding plane by utilizing packet filters which are easily
constructed and managed due to the uniqueness of the internal
infrastructure block.

Private Address Considerations

Private addresses are not appropriate for a number of reasons. A public
Internet network using private addresses internally may create confusion
if trace routes contain private addresses. Additional problems may
result due to wide spread filtering of private address space. ICMP
messages may get dropped due to such a policy. This can lead to
perceived odd behavior and make troubleshooting difficult.

Additionally, the consequences of accidentally routing private ip space
that is not globally unique, are potentially worse than if you
accidentally announced globally unique space.

DNS for private address space is today provided by blackhole-1.iana.org.
and blackhole-2.iana.org. A provider who wants to maintain forward and
reverse DNS sanity has to hijack those ip addresses to provide
consistent DNS resolution. This will cause any users who's traffic
transits that provider's network to also get 'inconsistent' answers with
respect to the private address space in question.

For management and troubleshooting purposes, it is important that
infrastructure which provides Internet route reachability be numbered
with addresses that resolve through DNS. Also, global uniqueness of
addressing is important in minimizing renumbering efforts as
organizations (and their networks) merge. RFC 4193 provides for neither
of these needs.

Timetable for implementation: Immediate

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