draft-ietf-grow-private-ip-sp-cores-02.txt   draft-ietf-grow-private-ip-sp-cores-03.txt 
Network Working Group A. Kirkham Network Working Group A. Kirkham
Internet-Draft Palo Alto Networks Internet-Draft Palo Alto Networks
Obsoletes: None (if approved) April 25, 2012 Obsoletes: None (if approved) May 7, 2012
Intended status: Informational Intended status: Informational
Expires: October 27, 2012 Expires: November 8, 2012
Issues with Private IP Addressing in the Internet Issues with Private IP Addressing in the Internet
draft-ietf-grow-private-ip-sp-cores-02 draft-ietf-grow-private-ip-sp-cores-03
Abstract Abstract
The purpose of this document is to provide a discussion of the The purpose of this document is to provide a discussion of the
potential problems of using private, RFC1918, or non-globally- potential problems of using private, RFC1918, or non-globally-
routable addressing within the core of an SP network. The discussion routable addressing within the core of an SP network. The discussion
focuses on link addresses and to a small extent loopback addresses. focuses on link addresses and to a small extent loopback addresses.
While many of the issues are well recognised within the ISP While many of the issues are well recognised within the ISP
community, there appears to be no document that collectively community, there appears to be no document that collectively
describes the issues. describes the issues.
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 27, 2012. This Internet-Draft will expire on November 8, 2012.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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4. Effects on Path MTU Discovery . . . . . . . . . . . . . . . . 7 4. Effects on Path MTU Discovery . . . . . . . . . . . . . . . . 7
5. Unexpected interactions with some NAT implementations . . . . 8 5. Unexpected interactions with some NAT implementations . . . . 8
6. Interactions with edge anti-spoofing techniques . . . . . . . 10 6. Interactions with edge anti-spoofing techniques . . . . . . . 10
7. Peering using loopbacks . . . . . . . . . . . . . . . . . . . 10 7. Peering using loopbacks . . . . . . . . . . . . . . . . . . . 10
8. DNS Interaction . . . . . . . . . . . . . . . . . . . . . . . 11 8. DNS Interaction . . . . . . . . . . . . . . . . . . . . . . . 11
9. Operational and Troubleshooting issues . . . . . . . . . . . . 11 9. Operational and Troubleshooting issues . . . . . . . . . . . . 11
10. Security Considerations . . . . . . . . . . . . . . . . . . . 12 10. Security Considerations . . . . . . . . . . . . . . . . . . . 12
11. Alternate approaches to core network security . . . . . . . . 13 11. Alternate approaches to core network security . . . . . . . . 13
12. Normative References . . . . . . . . . . . . . . . . . . . . . 14 12. Normative References . . . . . . . . . . . . . . . . . . . . . 14
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 14 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . . 14
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction 1. Introduction
In the mid to late 90's, some Internet Service Providers (ISPs) In the mid to late 90's, some Internet Service Providers (ISPs)
adopted the practice of utilising private (or non-globally unique) IP adopted the practice of utilising private (or non-globally unique) IP
(i.e. RFC1918) addresses for the infrastructure links and in some (i.e. RFC1918) addresses for the infrastructure links and in some
cases the loopback interfaces within their networks. The reasons for cases the loopback interfaces within their networks. The reasons for
this approach centered on conservation of address space (i.e. this approach centered on conservation of address space (i.e.
scarcity of public IPv4 address space), and security of the core scarcity of public IPv4 address space), and security of the core
network (also known as core hiding). network (also known as core hiding).
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3 198.51.100.9 20 msec 20 msec 32 msec 3 198.51.100.9 20 msec 20 msec 32 msec
4 10.1.1.5 20 msec 20 msec 20 msec 4 10.1.1.5 20 msec 20 msec 20 msec
5 10.1.1.1 20 msec 20 msec 20 msec 5 10.1.1.1 20 msec 20 msec 20 msec
R6# R6#
This effect in itself is often not a problem. However, if anti- This effect in itself is often not a problem. However, if anti-
spoofing controls are applied at network perimeters, then responses spoofing controls are applied at network perimeters, then responses
returned from hops with private IP addresses will be dropped. Anti- returned from hops with private IP addresses will be dropped. Anti-
spoofing refers to a security control where traffic with an invalid spoofing refers to a security control where traffic with an invalid
source address is discarded. Anti-spoofing is further described in source address is discarded. Anti-spoofing is further described in
BCP 38/RFC 2827. [BCP 38]/[RFC 2827].
The effects are illustrated in a second example below. The same The effects are illustrated in a second example below. The same
network as example 1 is used, but with the addition of anti-spoofing network as example 1 is used, but with the addition of anti-spoofing
deployed at the ingress of R4 on the R3-R4 interface (IP Address deployed at the ingress of R4 on the R3-R4 interface (IP Address
198.51.100.10). 198.51.100.10).
R6#traceroute 203.0.113.1 R6#traceroute 203.0.113.1
Type escape sequence to abort. Type escape sequence to abort.
Tracing the route to 203.0.113.1 Tracing the route to 203.0.113.1
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Tracing the route to 203.0.113.65 Tracing the route to 203.0.113.65
1 10.1.1.2 0 msec 4 msec 0 msec 1 10.1.1.2 0 msec 4 msec 0 msec
2 10.1.1.6 0 msec 4 msec 0 msec 2 10.1.1.6 0 msec 4 msec 0 msec
3 198.51.100.10 [AS 64497] 0 msec 4 msec 0 msec 3 198.51.100.10 [AS 64497] 0 msec 4 msec 0 msec
4 198.51.100.5 [AS 64497] 0 msec 0 msec 4 msec 4 198.51.100.5 [AS 64497] 0 msec 0 msec 4 msec
5 198.51.100.1 [AS 64497] 0 msec 0 msec 4 msec 5 198.51.100.1 [AS 64497] 0 msec 0 msec 4 msec
R1# R1#
It should be noted that some solutions to this problem have been It should be noted that some solutions to this problem have been
proposed in RFC 5837 which provides extensions to ICMP to allow the proposed in [RFC 5837] which provides extensions to ICMP to allow the
identification of interfaces and their components by any combination identification of interfaces and their components by any combination
of the following: ifIndex, IPv4 address, IPv6 address, name, and of the following: ifIndex, IPv4 address, IPv6 address, name, and
MTU. However at the time of writing, little or no deployment was MTU. However at the time of writing, little or no deployment was
known to be in place. known to be in place.
4. Effects on Path MTU Discovery 4. Effects on Path MTU Discovery
The Path MTU Discovery (PMTUD) process was designed to allow hosts to The Path MTU Discovery (PMTUD) process was designed to allow hosts to
make an accurate assessment of the maximum packet size that can be make an accurate assessment of the maximum packet size that can be
sent across a path without fragmentation. Path MTU Discovery is sent across a path without fragmentation. Path MTU Discovery is
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The issue is as follows: The issue is as follows:
o When an ICMP Type 3 Code 4 message is issued from an infrastructure o When an ICMP Type 3 Code 4 message is issued from an infrastructure
link that uses a private (RFC1918) address, it must be routed back to link that uses a private (RFC1918) address, it must be routed back to
the originating host. As the originating host will typically be a the originating host. As the originating host will typically be a
globally routable IP address, its source address is used as the globally routable IP address, its source address is used as the
destination address of the returned ICMP Type 3 packet. At this destination address of the returned ICMP Type 3 packet. At this
point there are normally no problems. point there are normally no problems.
o As the returned packet will have an RFC1918 source address, o As the returned packet will have an [RFC1918] source address,
problems can occur when the returned packet passes through an anti- problems can occur when the returned packet passes through an anti-
spoofing security control (such as Unicast RPF (uRPF)), other anti- spoofing security control (such as Unicast RPF (uRPF)), other anti-
spoofing ACLs, or virtually any perimeter firewall. These devices spoofing ACLs, or virtually any perimeter firewall. These devices
will typically drop packets with an RFC1918 source address, breaking will typically drop packets with an [RFC1918] source address,
the successful operation of PMTUD. breaking the successful operation of PMTUD.
As a result, the potential for application level issues may be As a result, the potential for application level issues may be
created. created.
5. Unexpected interactions with some NAT implementations 5. Unexpected interactions with some NAT implementations
Private addressing is legitimately used within many enterprise, Private addressing is legitimately used within many enterprise,
corporate or government networks for internal network addressing. corporate or government networks for internal network addressing.
When users on the inside of the network require Internet access, they When users on the inside of the network require Internet access, they
will typically connect through a perimeter router, firewall, or will typically connect through a perimeter router, firewall, or
network proxy, that provides Network Address Translation (NAT) or network proxy, that provides Network Address Translation (NAT) or
Network Address Port Translation (NAPT) services to a public Network Address Port Translation (NAPT) services to a public
interface. interface.
Scarcity of public IPv4 addresses, and the transition to IPv6, is Scarcity of public IPv4 addresses, and the transition to IPv6, is
forcing many service providers to make use of NAT. CGN (Carrier forcing many service providers to make use of NAT. CGN (Carrier
Grade NAT) will enable service providers to assign private RFC 1918 Grade NAT) will enable service providers to assign private [RFC 1918]
IPv4 addresses to their customers rather than public, globally unique IPv4 addresses to their customers rather than public, globally unique
IPv4 addresses. NAT444 will make use of a double NAT process. IPv4 addresses. NAT444 will make use of a double NAT process.
Unpredictable or confusing interactions could occur if traffic such Unpredictable or confusing interactions could occur if traffic such
as traceroute, PMTUD and possibly other applications were launched as traceroute, PMTUD and possibly other applications were launched
from the NAT IPv4 'inside address' and it passed over the same from the NAT IPv4 'inside address' and it passed over the same
address range in the public IP core. While such a situation would be address range in the public IP core. While such a situation would be
unlikely to occur if the NAT pools and the private infrastructure unlikely to occur if the NAT pools and the private infrastructure
addressing were under the same administration, such a situation could addressing were under the same administration, such a situation could
occur in the more typical situation of a NAT'ed corporate network occur in the more typical situation of a NAT'ed corporate network
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2 198.51.100.13 0 msec 4 msec 0 msec 2 198.51.100.13 0 msec 4 msec 0 msec
3 10.1.1.2 0 msec 4 msec 0 msec <<<< 3 10.1.1.2 0 msec 4 msec 0 msec <<<<
4 198.51.100.5 4 msec 0 msec 4 msec 4 198.51.100.5 4 msec 0 msec 4 msec
5 198.51.100.1 0 msec 0 msec 0 msec 5 198.51.100.1 0 msec 0 msec 0 msec
R1# R1#
This example has been included to illustrate an effect. Whether that This example has been included to illustrate an effect. Whether that
effect would be problematic would depend on both the deployment effect would be problematic would depend on both the deployment
scenario and the application in use. scenario and the application in use.
Certainly a scenario where the same RFC1918 address space becomes Certainly a scenario where the same [RFC1918] address space becomes
utilised on both the inside and outside interfaces of a NAT/NAPT utilised on both the inside and outside interfaces of a NAT/NAPT
device can be problematic. For example, the same private address device can be problematic. For example, the same private address
range is assigned by both the administrator of a corporate network range is assigned by both the administrator of a corporate network
and their ISP. Some applications discover the outside address of and their ISP. Some applications discover the outside address of
their local CPE to determine if that address is reserver for special their local CPE to determine if that address is reserver for special
use. Application behavior may then be based on this determination. use. Application behavior may then be based on this determination.
RFC6598 provides further analysis of this situation. [RFC6598] provides further analysis of this situation.
To address this scenario and others, RFC6598 requests a dedicated /10 To address this scenario and others, [RFC6598] requests a dedicated
address block for the purpose of Shared CGN (Carrier Grade NAT) /10 address block for the purpose of Shared CGN (Carrier Grade NAT)
Address Space. The purpose of Shared CGN Address Space is to number Address Space. The purpose of Shared CGN Address Space is to number
CPE (Customer Premise Equipment) interfaces that connect to CGN CPE (Customer Premise Equipment) interfaces that connect to CGN
devices. As explained in RFC6598, RFC1918 addressing has issues when devices. As explained in [RFC6598], [RFC1918] addressing has issues
used in this deployment scenario. when used in this deployment scenario.
6. Interactions with edge anti-spoofing techniques 6. Interactions with edge anti-spoofing techniques
Denial of Service Attacks (DOS) and Distributed Denial of Service Denial of Service Attacks (DOS) and Distributed Denial of Service
Attacks (DDoS) can make use of spoofed source IP addresses in an Attacks (DDoS) can make use of spoofed source IP addresses in an
attempt to obfuscate the source of an attack. RFC2827 (Network attempt to obfuscate the source of an attack. [RFC2827] (Network
Ingress Filtering) strongly recommends that providers of Internet Ingress Filtering) strongly recommends that providers of Internet
connectivity implement filtering to prevent packets using source connectivity implement filtering to prevent packets using source
addresses outside of their legitimately assigned and advertised addresses outside of their legitimately assigned and advertised
prefix ranges. Such filtering should also prevent packets with prefix ranges. Such filtering should also prevent packets with
private source addresses from egressing the AS. private source addresses from egressing the AS.
Best security practices for ISPs also strongly recommend that packets Best security practices for ISPs also strongly recommend that packets
with illegitimate source addresses should be dropped at the AS with illegitimate source addresses should be dropped at the AS
perimeter. Illegitimate source addresses includes private IP perimeter. Illegitimate source addresses includes private IP
(RFC1918) addresses, addresses within the provider's assigned prefix (RFC1918) addresses, addresses within the provider's assigned prefix
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not possible, or considerably more complex to implement. not possible, or considerably more complex to implement.
8. DNS Interaction 8. DNS Interaction
Many ISPs utilise their DNS to perform both forward and reverse Many ISPs utilise their DNS to perform both forward and reverse
resolution for the infrastructure devices and infrastructure resolution for the infrastructure devices and infrastructure
addresses. With a privately numbered core, the ISP itself will still addresses. With a privately numbered core, the ISP itself will still
have the capability to perform name resolution of their own have the capability to perform name resolution of their own
infrastructure. However others outside of the autonomous system will infrastructure. However others outside of the autonomous system will
not have this capability. At best, they will get a number of not have this capability. At best, they will get a number of
unidentified RFC1918 IP addresses returned from a traceroute. unidentified [RFC1918] IP addresses returned from a traceroute.
It is also worth noting that in some cases the reverse resolution It is also worth noting that in some cases the reverse resolution
requests may leak outside of the AS. Such a situation can add load requests may leak outside of the AS. Such a situation can add load
to public DNS servers. Further information on this problem is to public DNS servers. Further information on this problem is
documented in the internet draft "AS112 Nameserver Operations". documented in the internet draft "AS112 Nameserver Operations".
9. Operational and Troubleshooting issues 9. Operational and Troubleshooting issues
Previous sections of the document have noted issues relating to Previous sections of the document have noted issues relating to
network operations and troubleshooting. In particular when private network operations and troubleshooting. In particular when private
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and review - Dan Wing (Cisco Systems), Roland Dobbins (Arbor and review - Dan Wing (Cisco Systems), Roland Dobbins (Arbor
Networks), Philip Smith (APNIC), Barry Greene (ISC), Anton Ivanov Networks), Philip Smith (APNIC), Barry Greene (ISC), Anton Ivanov
(kot-begemot.co.uk), Ryan Mcdowell (Cisco Systems), Russ White (Cisco (kot-begemot.co.uk), Ryan Mcdowell (Cisco Systems), Russ White (Cisco
Systems), Gregg Schudel (Cisco Systems), Michael Behringer (Cisco Systems), Gregg Schudel (Cisco Systems), Michael Behringer (Cisco
Systems), Stephan Millet (Cisco Systems), Tom Petch (BT Connect), Wes Systems), Stephan Millet (Cisco Systems), Tom Petch (BT Connect), Wes
George (Time Warner Cable). George (Time Warner Cable).
The author would also like to acknowledge the use of a variety of The author would also like to acknowledge the use of a variety of
NANOG mail archives as references. NANOG mail archives as references.
Index
H
http://tools.ietf.org/html/draft-ietf-dnsop-as112-ops-08 11
http://tools.ietf.org/html/rfc2827 5
Author's Address Author's Address
Anthony Kirkham Anthony Kirkham
Palo Alto Networks Palo Alto Networks
Level 32, 101 Miller St Level 32, 101 Miller St
North Sydney, New South Wales 2060 North Sydney, New South Wales 2060
Australia Australia
Phone: +61 7 33530902 Phone: +61 7 33530902
Email: tkirkham@paloaltonetworks.com Email: tkirkham@paloaltonetworks.com
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