Internet DRAFT - draft-lewis-infrastructure-security
draft-lewis-infrastructure-security
INTERNET-DRAFT Darrel Lewis
James Gill
Verizon Business.
Darrel Lewis
Cisco Systems, Inc.
Paul Quinn
Cisco Systems, Inc.
Peter Schoenmaker
NTT America
October 2006
Service Provider Infrastructure Security
<draft-lewis-infrastructure-security-00>
Status of this Memo
Status of this Memo
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Copyright Notice
Copyright (C) The Internet Society (2006)
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http://www.ietf.org/shadow.html.
This Internet-Draft will expire on October 28, 2006.
Copyright Notice
Copyright (C) The Internet Society (2006). All Rights Reserved.
Abstract
This RFC defines best current practices for implementing Service
Provider network infrastructure protection for network elements.
This RFC complements and extends RFC 2267 and RFC 3704. RFC 2267
provides guidelines for filtering traffic on the ingress to service
provider networks. RFC 3704 expands the recommendations described in
RFC 2267 to address operational filtering guidelines for single and
multi-homed environments. The focus of those RFCs is on filtering
ingress packets ingress, regardless of destination, if those packets
are have spoofed source address or fall within "reserved" address
space. Deployment of RFCs 2267 and 3704 has limited the effects of
denial of service attacks by dropping ingress packets with spoofed
source addresses, which in turn offers other benefits by ensuring
that packets coming into a network originate from validly allocated
and consistent sources.
This document focuses solely on traffic destined to the network
infrastructure itself to protect the network from denial of service
and other attacks. This document presents techniques that, together
with network edge ingress filtering and RFC 2267 and RFC 3704, create
a layered approach for infrastructure protection.
This document does not present recommendations for protocol
validation (i.e. "sanity checking") nor does it address guidelines
for general security configuration.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Overview of Infrastructure Protection Techniques . . . . . . . 5
2.1. Edge Infrastructure Access Control Lists. . . . . . . . . . 5
2.2. Edge Remarking. . . . . . . . . . . . . . . . . . . . . . . 5
2.3. Device and Element Protection . . . . . . . . . . . . . . . 6
2.4. Infrastructure Hiding . . . . . . . . . . . . . . . . . . . 6
3. Edge Infrastructure Access Control Lists . . . . . . . . . . . 6
3.1. Constructing the Access List. . . . . . . . . . . . . . . . 7
3.2. Other Traffic . . . . . . . . . . . . . . . . . . . . . . . 7
3.3. Edge Infrastructure Conclusion. . . . . . . . . . . . . . . 8
4. Edge Rewrite/Remarking . . . . . . . . . . . . . . . . . . . . 8
4.1. Edge Rewriting/Remarking Discussion . . . . . . . . . . . . 9
5. Device/Element Protection. . . . . . . . . . . . . . . . . . . 9
5.1. Service Specific Access Control . . . . . . . . . . . . . . 10
5.1.1. Common Services. . . . . . . . . . . . . . . . . . . . . 10
5.2. Aggregate Device Access Control . . . . . . . . . . . . . . 10
5.2.1. IP Fragments . . . . . . . . . . . . . . . . . . . . . . 11
5.2.2. Performance Considerations . . . . . . . . . . . . . . . 11
5.2.3. Access Control Implementation Guide. . . . . . . . . . . 11
5.3. Device Access Authorization and Accounting. . . . . . . . . 11
6. Infrastructure Hiding. . . . . . . . . . . . . . . . . . . . . 12
6.1. Use less IP. . . . . . . . . . . . . . . . . . . . . . . . 12
6.2. MPLS techniques . . . . . . . . . . . . . . . . . . . . . . 12
6.3. IGP configuration . . . . . . . . . . . . . . . . . . . . . 12
6.4. Route advertisement control . . . . . . . . . . . . . . . . 13
6.4.1. Route Announcement filtering . . . . . . . . . . . . . . 13
6.4.2. Address core out of rfc1918 space. . . . . . . . . . . . 13
7. IPv6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.1. IPv6 Edge Infrastructure Access Control List. . . . . . . . 14
7.2. IPv6 Edge Remarking . . . . . . . . . . . . . . . . . . . . 14
7.3. IPv6 Device and Element Protection. . . . . . . . . . . . . 15
7.4. IPv6 Infrastructure Hiding. . . . . . . . . . . . . . . . . 15
8. IP Multicast . . . . . . . . . . . . . . . . . . . . . . . . . 15
8.1. Multicast Group Protection. . . . . . . . . . . . . . . . . 16
8.2. Performance Considerations. . . . . . . . . . . . . . . . . 16
8.3. IPv6 and Multicast. . . . . . . . . . . . . . . . . . . . . 16
9. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . 17
10. References. . . . . . . . . . . . . . . . . . . . . . . . . . 18
10.1. Normative References . . . . . . . . . . . . . . . . . . . 18
10.2. Informative References . . . . . . . . . . . . . . . . . . 18
11. Authors' Addresses. . . . . . . . . . . . . . . . . . . . . . 19
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1. Introduction
This RFC defines best current practices for implementing Service
Provider network infrastructure protection for network elements.
RFC 2267 and RFC 3704 focuses on limiting the effects of denial of
service attacks by filtering ingress packets with spoofed source
addresses, which in turn offers other benefits by ensuring that
packets coming into a network originate from validly allocated and
consistent sources. RFC 3704 extends the recommendations described
in RFC 2267 to address operational filtering guidelines for single
and multi-homed environments. In both cases (RFC 2267 and RFC 3704),
the focus is on dropping packets on ingress, regardless of
destination, if those packets are have spoofed source address or fall
within "reserved" address space. This document both refines and
extends the filtering best practices outlined in RFC 2267 and RFC
3704 and focuses only on traffic destined to the network
infrastructure itself to protect the service provider network from
denial of service and other attacks. This document presents
techniques that, together with network edge ingress filtering and RFC
2267 and RFC 3704, create a layered approach for infrastructure
protection.
Denial of Service (DoS) attacks are common and the network
infrastructure itself is a target. Attacks targeting the network
infrastructure can take many forms, ranging from bandwidth saturation
to crafted packets destined to a router. These attacks might use
spoofed source address or they might use the true address of source
of the traffic. Regardless of the nature of the attack, the network
infrastructure must be protected from both accidental and intentional
attacks.
The techniques outlined in this document and described in section 2
below, provide a layered approach for infrastructure protection:
Edge policy (filtering and precedence), per device traffic policy
enforcement for packets destined to a device and finally,
routing/address advertising best practices to limit core network --
that is P and PE infrastructure -- exposure.
This document is aimed at network operators who would like to
"harden" their infrastructure and make it more resilient to external
attack. These techniques are designed to be used in addition to
specific protocol or application security features implemented in
network devices.
Infrastructure protection is a complex topic, improving protection is
always beneficial.
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2. Overview of Infrastructure Protection Techniques
This section provides an overview of the four recommended techniques
that may be used to protect network infrastructure. The details of
each area along with some deployment consideration are described in
detail in subsequent sections.
- Edge Infrastructure Access Control List
- Edge Remarking
- Device and Element Protection
- Infrastructure Hiding
The above list is not exhaustive; other mechanisms can be used to
provide a measure of protection. The techniques discussed in this
document have been widely deployment and have proven operational
security benefits in large networks.
2.1. Edge Infrastructure Access Control Lists
Edge infrastructure access control lists are ingress access control
lists that filter traffic destined to the network only. They should
permit all traffic through the network. Explicit filtering of
traffic destined to network devices creates a first level of
protection at the network edge: only traffic explicitly permitted
into the network can reach a device beyond the PE router with the
filter.
Although very effective, edge infrastructure access control lists are
not perfect and, like any filter lists, must be maintained and
updated. Furthermore, while widespread deployment on ingress
interface provides the most protection (which in some cases will not
be possible), some deployment is better than no deployment.
2.2. Edge Remarking
We define Edge Remarking as ensuring that ingress IP precedence or
DSCP values match expected values within the context of security.
This provides another layer of defense particularly for traffic
permitted through any of the Edge Infrastructure Access Control
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Lists. In this RFC we focus only on using Edge Remarking best
practices to enforce security policies.
2.3. Device and Element Protection
Each device infrastructure device should enforce local rules for
traffic destined to the device itself. These rules can take the form
of filters (permit/deny) or rate limiting rules that allow ingress
traffic at specified rates. These should complement any existing
Edge Infrastructure Access Control Lists.
The deployment of these local device protection rules compliments the
edge techniques by protecting the device from traffic that: i) was
permitted but violates device policy, ii) could not be filtered at
the edge, iii) entered the network on an interface that did not have
ingress filtering enabled.
2.4. Infrastructure Hiding
Hiding the infrastructure of the network provides an elegant
mechanism for protecting the network infrastructure. If the
destination of an attack is to an infrastructure address that is
unreachable, attacks become far more difficult. Infrastructure
hiding can be achieved in several ways:
- MPLS techniques
- IGP configuration
- Route advertisement control
3. Edge Infrastructure Access Control Lists
Edge Infrastructure Access Control Lists (EIACLs) are a specific
implementation of the more general Ingress Access List. As opposed
to generic ingress filtering which denies data (sometimes referred to
as user) plane traffic, edge infrastructure access control lists do
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not attempt to deny traffic going through the devices, rather this
form of access control limits traffic destined to infrastructure
equipment while permitting -- if needed, explicitly -- traffic
through the network.
3.1. Constructing the Access List
Edge Infrastructure Access Control Lists permit only required traffic
to the network infrastructure, while allowing data plane traffic to
flow through unaffected. The basic premise of EIACLs is that only a
relatively limited subset of traffic, sourced from outside your AS,
needs to be destined for a core router and that by explicitly
permitting only that known and understood traffic, the core devices
are not subjected to unnecessary traffic that might result in a
denial of service attack.
Since edge infrastructure access control lists protect only the
infrastructure, the development of the list differs somewhat from
"traditional" access filter lists:
1. Review addressing scheme, and identify address block(s)
that represent core devices.
2. Determine what traffic must be destined to the core devices
from outside the AS.
3. Create a filter that allow the required traffic, denies all
traffic destined to the core address block and then finally, permits
all other traffic to all.
As with other ingress filtering techniques, EIACLs are applied on
ingress into the network, and clearly comprehensive coverage (i.e. on
as many interface as possible) yields the most protection.
3.2. Other Traffic
In addition to the explicitly permitted traffic, EIACLs can be
combined with other common edge filters such as:
1. Source spoof prevention (as per RFC 3704) by denying
internal AS addresses as external sources.
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2. Filtering of reserved addresses (e.g. rfc1918 addresses) as
traffic should not be sourced from reserved address.
3. Other unneeded or unnecessary traffic
Filtering this traffic can be part of the list explicitly or
implicitly, however, explicit filters often provides log-able
information that can be of use during a security event.
3.3. Edge Infrastructure Conclusion
Edge Infrastructure Access Control Lists provide a very effective
first line of defense. To deploy them effectively, core address
space must be identifiable and widespread deployment is necessary.
4. Edge Rewrite/Remarking
RFC 1812 section 5.3 defines the use of IP Preference in IPv4 packets
for routing, management and control traffic. In addition it
recommends devices use a mechanism for providing preferential
forwarding for packets marked as routing, management or control
traffic using IP Preference bits 6 or 7 (110 or 111 in binary.)
RFC2474 defines DSCP and the compatibility of IP Preference bits when
using DSCP.
All packets received from the Customer edge (CE,) and the Peer Edge
by the Provider Edge (PE,) with IP Preference values of 6 or 7 or
DSCP bits of 11xxxx, as specified in RFC2474 Differentiated Services
Field Definition, should have the IP Preference bits rewritten.
Routing traffic received from the CE and the Peer Edge can safely
have the IP Preference bits rewritten, because only a limited number
of protocols are transmitted beyond the first PE router. The bits
may be rewritten to any value other than IP Preference values 6 or 7,
or any DSCP value other than 11xxxx. The new value can be based on
the network operators IP Preference or DSCP policy. If no policy
exists the bits should be rewritten to 0.
Providers may not want to modify traffic that goes through their
network in an effort offer a fully transparent service. If the
provider relies on alternative means of classifying traffic for
prioritized forwarding rewriting the IP Preference bits is not
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required. Alternatives include encapsulating customer traffic into a
second protocol, such as MPLS, GRE, and IP, or using an Access
Control List (ACL) to classify legitimate routing, management, and
control traffic. When encapsulating traffic into a second protocol,
policy must ensure that IP Preference bits 6 and 7 are not
transferred to the preference field of encapsulating protocol. In
this example the EXP bits or IP Preference/DSCP bits. A longer tuple
used for identifying routing, management and control traffic will
provide a higher level of security than a shorter one. Other
techniques may exist not covered in this document.
4.1. Edge Rewriting/Remarking Discussion
By default router vendors do not differentiate an interface on a PE
router connected to a P router from an interface connected to a CE
router. As a result any packet with the proper IP Preference or DSCP
bits set may receive the same preferential forwarding behavior as
legitimate routing, management, and control traffic. A malicious
attack may be able to take advantage of the vulnerability to increase
the effectiveness of the attack or to attack the routing, management,
and/or control traffic directly.
This document is aimed at protecting network infrastructure from
traffic to the device rather than traffic through the device. Even
though the edge rewrite/remarking deals primarily with traffic
through a device it is included because the traffic has a direct
impact on traffic to a device. The forwarding prioritization given
to routing, management, and control traffic by default leaves devices
vulnerable to indirect attacks to the core infrastructure.
5. Device/Element Protection
Even with the widest possible deployment of the techniques described
above in the section Infrastructure Edge Access Control, the
individual devices of the network must implement access control
mechanisms. This is because in addition to the case of incomplete or
imperfect deployment of edge infrastructure control, threats may
occur from trusted sources within the perimeter of the network.
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5.1. Service Specific Access Control
Typically these mechanisms are not concerned with protecting the
system as a whole, but the service from exploitation. The goal is
not overall system availability, but maximizing the security of the
particular service.
5.1.1. Common Services
While each service implemented by network equipment manufacturers
differs in its available security features there are some common
services and security features for those services that have been
widely deployed.
The most important first step for the operator is to disable any
unneeded/unused services.
Second, the operator should utilize the services access control
mechanisms to limit the access to the devices service to only
required sources. Examples are using virtual terminal access control
lists, or SNMP Community access control lists.
5.2. Aggregate Device Access Control
The device must be protected from denial of service threats, in
addition, aggregating the security policy allows for a simplified
view of the access policies traffic going to the device.
A key requirement of these mechanisms is that it must not impact
transit data plane traffic. In addition, these mechanisms should not
make the device more vulnerable to malicious traffic than not using
them.
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5.2.1. IP Fragments
Traffic destined to a router is not typically fragmented. Fragment
keywords or other mechanisms to deny fragments to the device are
recommended.
5.2.2. Performance Considerations
Care should be taken to understand a vendors implementation of this
functionality and to make sure that device operation is not impaired
during DoS attacks against the device.
5.2.3. Access Control Implementation Guide
Implementing a complex set of access controls for all traffic going
to and from a router is non trivial. The following is a recommended
set of steps that has been used successfully by many carriers.
-Develop list of required protocols
-Develop source address requirements
-Determine destination interface on router
Does the protocol access a single interface?
Does the protocol access many interfaces?
Does the protocol access a virtual or physical interfaces?
-Deployment should be an iterative process
-Start with relatively open lists then tighten as needed
5.3. Device Access Authorization and Accounting
Operators should use per command authorization and accounting
wherever possible. Aside from their utility in mitigating other
security threats, they provide an invaluable tool in the post event
forensics.
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6. Infrastructure Hiding
Hiding the infrastructure of the network provides an elegant
mechanism for protecting the network infrastructure. If the
destination of an attack is to an infrastructure address that is
unreachable, attacks become far more difficult. Infrastructure
hiding can be achieved in several ways:
6.1. Use less IP
One way to reduce exposure of network infrastructure is to use
unnumbered links wherever possible. This is particularly useful for
customers in the simple case of a single provider with a default path
to the Internet.
6.2. MPLS techniques
While it may not be feasible to hide the entire infrastructure of
large networks from edge to edge using MPLS, it is certainly possible
to reduce exposure of critical core infrastructure beyond the first
hop by creating an MPLS mesh where TTL is not decremented as packets
pass through it. In this manner the number, addresses, and even
existence of intermediary devices can be hidden from traffic as it
passes through the core.
6.3. IGP configuration
Using a non-IP control plane for the core routing protocol can
substantially reduce the number of IP addresses that
[comprise/expose] the core. This simplifies the task of maintaining
edge ACLs or route announcement filters. IS-IS is an elegant and
mature protocol that may be suitable for this task.
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6.4. Route advertisement control
6.4.1. Route Announcement filtering
Inasmuch as it is unavoidable that some network elements must be
configured with IP addresses, it may be possible to assign these
address out of netblocks for which the routing advertisement can be
filtered, thereby limiting possible sources of traffic to core
netblocks down to customers for which you provide a default route, or
direct peers who would make the effort to create a static route for
your core netblock into your AS.
Further, it may be possible in those situations where customer point-
to-point links must be numbered, to address such links out of another
range of addresses for which announcements could be similarly
filtered. While this has implications for a customer's ability to
remote-monitor their circuit, this can often be overcome with
application of an address from the customer's routed space to the CPE
loopback.
6.4.2. Address core out of rfc1918 space
In addition to filtering the visibility of core addresses to the
wider Internet, it may be possible to use rfc1918 netblocks for
numbering infrastructure when IP addresses are required (eg,
loopbacks). This added level of obscurity takes prevention of wide
distribution of your infrastructure address space one step further.
Many networks filter out packets with rfc1918 address at
ingress/egress points as a matter of course. In this circumstance,
tools such as traceroute can work through your core, but reverse-
resolution of descriptive names should be restricted to queries from
internal/support groups.
7. IPv6
IPv6 Networks contain the same infrastructure security risks as IPv4.
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All techniques described in this document for IPv4 should be directly
applicable to IPv6 networks. Limitations exist where devices do not
have feature parity between IPv4 and IPv6. Different techniques
maybe required where IPv4 and IPv6 networks deviate in
implementation. Multi-vendor networks create greater difficulties
when each vendor does not have feature parity with each other.
Hardware differences in devices that support both IPv4 and IPv6 must
also be taken into consideration. Because IPv6 uses a longer address
space the scaling, and performance characteristics of ACLs maybe
lower for IPv6 vs IPv4. The fields or number of fields that an ACL
can match on may also differ.
The fact that all PE devices do not support all the recommended ipv6
security features should not preclude the implementation of the
recommendations in this document on the devices that do support the
security features.
With the number of Network Operators deploying IPv6 growing, along
with the continued availability of IPv6 Tunnel services, connecting
to the IPv6 internet is less difficult. Dual stack IPv6 networks run
on 10Gbps and greater backbones with edge speeds equal to IPv4.
Neither the edge nor the core limit potential IPv6 attacks.
7.1. IPv6 Edge Infrastructure Access Control List
The same process should be used for constructing the IPv6 eiacl as
the IPv4 eiacl.
7.2. IPv6 Edge Remarking
IPv6 DSCP bits should be rewritten in the same manner that IPv4 DSCP
bits.
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7.3. IPv6 Device and Element Protection
IPv6 device and element protection should be implemented using the
same policy as IPv4.
7.4. IPv6 Infrastructure Hiding
Network operators may deploy IPv4 differently from IPv6 in their
network. Providers may use native forwarding for IPv6 while using
MPLS for IPv4, other combinations. IPv6 infrastructure hiding should
have parity with IPv4 infrastructure hiding even if the technique
used is different.
Implementation of IPv6 route advertisement control for infrastructure
hiding is difficult when using global address space. It is difficult
to get non-continuous network blocks from the address registries, and
de-aggregation of IPv6 address space is not an acceptable
alternative. It is still possible to use private address space as a
way of restricting IPv6 advertisements.
8. IP Multicast
IP Multicast behaves differently from IP unicast therefore must be
secured in a different manner. Some of the protocols used with
Multicast rely on IP unicast to transport the routing, and control
information. Unicast based protocols should be secured using the
technique described in much of this document. Because this document
is focused on hardening a service providers infrastructure rather
than validating routing announcements, much of IP Multicast filtering
will be better covered in other documents.
In much the same way a host must listen on a certain IP address and
port for an IP unicast connection, Multicast must join a group in
order to receive any information via Multicast. The major difference
is that multicast groups are global and not assigned to a specific
customer or end user. Administrative boundaries and scope are
created to isolate Multicast groups within one network or desired
area.
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8.1. Multicast Group Protection
Certain Multicast groups should never been joined from outside an
operators network or administrative boundary. Filters should be
placed on the protocols used to communicate with external hosts and
networks. IGMP should have a join filter to prevent hosts from
joining internal groups. MSDP should be configured with a Source
Address (SA) filter to prevent other networks from joining internal
groups.
EIACLs should include administratively bounded multicast groups,
along with any groups used for protocols internal to a providers
network.
When constructing router Access Control as described in section
5.2.4, multicast protocols must be taken into consideration.
8.2. Performance Considerations
Multicast protocols and implementation have different performance and
scaling limitation than IP unicast. Multicast users create state on
the router every time the user joins a group. Router resources can
be exhausted if the amount of state created exceeds the resources
available on the router. Placing limits on the resources used by the
Multicast protocols can prevent collateral damage to services other
than Multicast on a router. MSDP should have a limit placed on the
number of SA announcements received. A fixed limit should be placed
on the number of entries the router stores in the IP Multicast
routing table. The number of SAP entries should have a limit placed
on them.
8.3. IPv6 and Multicast
IPv6 Multicast policy should be consistent with the IP Multicast
policy. 9.0 Security Considerations
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9. Acknowledgments
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10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", BCP 14, RFC 2119,
March 1997.
[REF] Reference....
10.2. Informative References
[RFC3667] Bradner, S., "IETF Rights in Contributions",
BCP 78, RFC 3667, February, 2004.
[RFC3668] Bradner, S., "Intellectual Property Rights in
IETF Technology", BCP 79, RFC 3668, February,
2004.
[RFC2434] Narten, T., and H. Alvestrand, "Guidelines for
Writing an IANA Considerations Section in RFCs",
BCP 26, RFC 2434, October 1998.
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11. Authors' Addresses
James Gill
TBD
Darrel Lewis
Cisco Systems Inc.
170 West Tasman Drive
San Jose, CA 95134
Phone: +1 408 853 3653
EMail: darlewis@cisco.com
Paul Quinn
170 West Tasman Drive
San Jose, CA 95134
Phone: +1 408 527 3560
Email: paulq@cisco.com
Peter Schoenmaker
NTT America
101 Park Ave., FL 41
New York, NY 10178
+1-212-808-2298
pds@ntt.net
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Gill, Lewis, Quinn, Schoenmaker Section 11. [Page 20]
