OPSEC M. Kaeo
Internet-Draft Double Shot Security, Inc.
Intended status: Informational August 29, 2006
Expires: March 2, 2007
Operational Security Current Practices
draft-ietf-opsec-current-practices-07
Status of this Memo
By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on March 2, 2007.
Copyright Notice
Copyright (C) The Internet Society (2006).
Kaeo Expires March 2, 2007 [Page 1]
Internet-Draft OPSEC Practices August 2006
Abstract
This document is a survey of the current practices used in today's
large ISP operational networks to secure layer 2 and layer 3
infrastructure devices. The information listed here is the result of
information gathered from people directly responsible for defining
and implementing secure infrastructures in Internet Service Provider
environments.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Threat Model . . . . . . . . . . . . . . . . . . . . . . . 3
1.3. Attack Sources . . . . . . . . . . . . . . . . . . . . . . 4
1.4. Operational Security Impact from Threats . . . . . . . . . 6
1.5. Document Layout . . . . . . . . . . . . . . . . . . . . . 7
2. Protected Operational Functions . . . . . . . . . . . . . . . 9
2.1. Device Physical Access . . . . . . . . . . . . . . . . . . 9
2.2. Device Management - In-Band and Out-of-Band (OOB) . . . . 11
2.3. Data Path . . . . . . . . . . . . . . . . . . . . . . . . 17
2.4. Routing Control Plane . . . . . . . . . . . . . . . . . . 19
2.5. Software Upgrades and Configuration Integrity /
Validation . . . . . . . . . . . . . . . . . . . . . . . . 23
2.6. Logging Considerations . . . . . . . . . . . . . . . . . . 27
2.7. Filtering Considerations . . . . . . . . . . . . . . . . . 30
2.8. Denial of Service Tracking / Tracing . . . . . . . . . . . 31
3. Security Considerations . . . . . . . . . . . . . . . . . . . 34
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 35
5. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 36
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 37
6.1. Normative References . . . . . . . . . . . . . . . . . . . 37
6.2. Informational References . . . . . . . . . . . . . . . . . 37
Appendix A. Protocol Specific Attacks . . . . . . . . . . . . . . 39
A.1. Layer 2 Attacks . . . . . . . . . . . . . . . . . . . . . 39
A.2. IPv4 Protocol Based Attacks . . . . . . . . . . . . . . . 39
A.3. IPv6 Attacks . . . . . . . . . . . . . . . . . . . . . . . 41
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 42
Intellectual Property and Copyright Statements . . . . . . . . . . 43
Kaeo Expires March 2, 2007 [Page 2]
Internet-Draft OPSEC Practices August 2006
1. Introduction
Security practices are well understood by the network operators who
have for many years gone through the growing pains of securing their
network infrastructures. However, there does not exist a written
document that enumerates these security practices. Network attacks
are continually increasing and although it is not necessarily the
role of an ISP to act as the Internet police, each ISP has to ensure
that certain security practices are followed to ensure that their
network is operationally available for their customers. This
document is the result of a survey conducted to find out what current
security practices are being deployed to secure network
infrastructures.
1.1. Scope
The scope for this survey is restricted to security practices that
mitigate exposure to risks with the potential to adversely impact
network availability and reliability. Securing the actual data
traffic is outside the scope of the conducted survey. This document
focuses solely on documenting currently deployed security mechanisms
for layer 2 and layer 3 network infrastructure devices. Although
primarily focused on IPv4, many of the same practices can (and
should) apply to IPv6 networks. Both IPv4 and IPv6 network
infrastructures are taken into account in this survey.
1.2. Threat Model
A threat is a potential for a security violation, which exists when
there is a circumstance, capability, action, or event that could
breach security and cause harm [RFC2828]. Every operational network
is subject to a multitude of threat actions, or attacks, i.e. an
assault on system security that derives from an intelligent act that
is a deliberate attempt to evade security services and violate the
security policy of a system [RFC2828]. Many of the threats to a
network infrastructure occur from an instantiation (or combination)
of the following:
Reconnaissance: An attack whereby information is gathered to
ascertain the network topology or specific device information which
can be further used to exploit known vulnerabilities
Man-In-The-Middle: An attack where a malicious user impersonates
either the sender or recipient of a communication stream while
inserting, modifying or dropping certain traffic. This type of
attack also covers phishing and session hijacks.
Protocol Vulnerability Exploitation: An attack which takes advantage
Kaeo Expires March 2, 2007 [Page 3]
Internet-Draft OPSEC Practices August 2006
of known protocol vulnerabilities due to design or implementation
flaws to cause inappropriate behavior.
Message Insertion: This can be a valid message (which could be a
reply attack, which is a scenario where a message is captured and
resent at later time). A message can also be inserted with any of
the fields in the message being OspoofedO, such as IP addresses, port
numbers, header fields or even packet content. Flooding is also part
of this threat instantiation.
Message Diversion/Deletion: An attack where legitimate messages are
removed before they can reach the desired recipient or are re-
directed to a network segment that is normally not part of the data
path.
Message Modification: This is a subset of a message insertion attack
where a previous message has been captured and modified before being
retransmitted. The message can be captured by using a man-in-the-
middle attack or message diversion.
Note that sometimes Denial of service attacks are listed as separate
categories. A denial of service is a consequence of an attack and
can be the result of too much traffic (i.e. flooding), or exploiting
protocol exploitation or inserting/deleting/diverting/modifying
messages.
1.3. Attack Sources
These attacks can be sourced in a variety of ways:
Active vs passive attacks
An active attack involves writing data to the network. It is
common practice in active attacks to disguise one's address and
conceal the identity of the traffic sender. A passive attack
involves only reading information off the network. This is
possible if the attacker has control of a host in the
communications path between two victim machines or has compromised
the routing infrastructure to specifically arrange that traffic
pass through a compromised machine. There are also situations
where mirrored traffic (often used for debugging, performance
monitoring or accounting purposes) is diverted to a compromised
machine which would not necessarily subvert any existing topology
and could be harder to detect. In general, the goal of a passive
attack is to obtain information that the sender and receiver would
prefer to remain private. [RFC3552]
Kaeo Expires March 2, 2007 [Page 4]
Internet-Draft OPSEC Practices August 2006
On-path vs off-path attacks
In order for a datagram to be transmitted from one host to
another, it generally must traverse some set of intermediate links
and routers. Such routers are naturally able to read, modify, or
remove any datagram transmitted along that path. This makes it
much easier to mount a wide variety of attacks if you are on-path.
Off-path hosts can transmit arbitrary datagrams that appear to
come from any hosts but cannot necessarily receive datagrams
intended for other hosts. Thus, if an attack depends on being
able to receive data, off-path hosts must first subvert the
topology in order to place themselves on-path. This is by no
means impossible but is not necessarily trivial. [RFC3552] A more
subtle attack is one where the traffic mirroring capability of a
device is hijacked and the traffic is diverted to a compromised
host since the network topology may not need to be subverted.
Insider or outsider attacks
An "insider attack" is one which is initiated from inside a given
security perimeter, by an entity that is authorized to access
system resources but uses them in a way not approved by those who
granted the authorization. An "outside attack" is initiated from
outside the perimeter, by an unauthorized or illegitimate user of
the system.
Deliberate attacks vs unintentional events
A deliberate attack is one where a miscreant intentionally
performs an assault on system security. However, there are also
instances where unintentional events cause the same harm yet are
performed without malice in mind. Configuration errors and
software bugs can be as devastating to network availability as any
deliberate attack on the network infrastructure.
The attack source can be a combination of any of the above, all of
which need to be considered when trying to ascertain what impact any
attack can have on the availability and reliability of the network.
It is nearly impossible to stop insider attacks or unintentional
events. However, if appropriate monitoring mechanisms are in place,
these attacks can also be detected and mitigated as with any other
attack source. The amount of effort it takes to identify and trace
an attack is of course dependent on the resourcefulness of the
attacker. Any of the specific attacks discussed further in this
document will elaborate on malicious behavior which are sourced by an
"outsider" and are deliberate attacks. Some further elaboration will
Kaeo Expires March 2, 2007 [Page 5]
Internet-Draft OPSEC Practices August 2006
be given to the feasibility of passive vs active and on-path vs off-
path attacks to show the motivation behind deploying certain security
features.
1.4. Operational Security Impact from Threats
The main concern for any of the potential attack scenarios is the
impact and harm it can cause to the network infrastructure. The
threat consequences are the security violations which results from a
threat action, i.e. an attack. These are typically classified as
follows:
(Unauthorized) Disclosure
A circumstance or event whereby an entity gains access to data for
which the entity is not authorized.
Deception
A circumstance or event that may result in an authorized entity
receiving false data and believing it to be true.
Disruption
A circumstance or event that interrupts or prevents the correct
operation of system services and functions. A broad variety of
attacks, collectively called denial of service attacks, threaten
the availability of systems and bandwidth to legitimate users.
Many such attacks are designed to consume machine resources,
making it difficult or impossible to serve legitimate users.
Other attacks cause the target machine to crash, completely
denying service to users.
Usurpation
A circumstance or event that results in control of system services
or functions by an unauthorized entity. Most network
infrastructure systems are only intended to be completely
accessible to certain authorized individuals. Should an
unauthorized person gain access to critical layer 2 / layer 3
infrastructure devices or services, they could cause great harm to
the reliability and availability of the network.
A complete description of threat actions that can cause these threat
Kaeo Expires March 2, 2007 [Page 6]
Internet-Draft OPSEC Practices August 2006
consequences can be found in [RFC2828]. Typically, a number of
different network attacks are used in combination to cause one or
more of the above mentioned threat consequences. An example would be
a malicious user who has the capability to eavesdrop on traffic.
First, he may listen in on traffic for a while to do some
reconnaissance work and ascertain which IP addresses belonged to
specific devices such as routers. Were this miscreant to obtain
information such as a router password sent in cleartext, he can then
proceed to compromise the actual router. From there, the miscreant
can launch various active attacks such as sending bogus routing
updates to redirect traffic or capture additional traffic to
compromise other network devices.
1.5. Document Layout
This document is a survey of current operational practices that
mitigate the risk of being susceptible to any threat actions. As
such, the main focus is on the currently deployed security practices
used to detect and/or mitigate attacks. The top-level categories in
this document are based on operational functions for ISPs and
generally relate to what is to be protected. This is followed by a
description of which attacks are possible and the security practices
currently deployed which will provide the necessary security services
to help mitigate these attacks. These security services are
classified as:
o User Authentication
o User Authorization
o Data Origin Authentication
o Access Control
o Data Integrity
o Data Confidentiality
o Auditing / Logging
o DoS Mitigation
In many instances, a specific protocol currently deployed will offer
a combination of these services. For example, AAA can offer user
authentication, user authorization and audit / logging services while
SSH can provide data origin authentication, data integrity and data
confidentiality. The services offered are more important than the
Kaeo Expires March 2, 2007 [Page 7]
Internet-Draft OPSEC Practices August 2006
actual protocol used. Note that access control will refer basically
to logical access control, i.e. filtering. Each section ends with an
additional considerations section which explains why specific
protocols may or may not be used and also gives some information
regarding capabilities which are not possible today due to bugs or
lack of ease of use.
Kaeo Expires March 2, 2007 [Page 8]
Internet-Draft OPSEC Practices August 2006
2. Protected Operational Functions
2.1. Device Physical Access
Device physical access pertains to protecting the physical location
and access of the layer 2 or layer 3 network infrastructure device.
Physical security is a large field of study/practice in and of
itself, arguably the largest, oldest and most well understood area of
security. Although it is important to have contingency plans for
natural disasters such as earthquakes and floods which can cause
damage to networking devices, this is out-of-scope for this document.
Here we concern ourselves with protecting access to the physical
location and how a device can be further protected from unauthorized
access if the physical location has been compromised, i.e protecting
the console access. This is aimed largely at stopping an intruder
with physical access from gaining operational control of the
device(s). Note that nothing will stop an attacker with physical
access from effecting a denial of service attack, which can be easily
accomplished by powering off the device or just unplugging some
cables.
2.1.1. Threats / Attacks
If any intruder gets physical access to a layer 2 or layer 3 device,
the entire network infrastructure can be under the control of the
intruder. At a minimum, the intruder can take the compromised device
out-of-service, causing network disruption, the extent of which
depends on the network topology. A worse scenario is where the
intruder can use this device to crack the console password and have
complete control of the device, perhaps without anyone detecting such
a compromise, or to attach another network device onto a port and
siphon off data with which the intruder can ascertain the network
topology and take control of the entire network.
The threat of gaining physical access can be realized in a variety of
ways even if critical devices are under high-security. There still
occur cases where attackers have impersonated maintenance workers to
gain physical access to critical devices that have caused major
outages and privacy compromises. Insider attacks from authorized
personnel also pose a real threat and must be adequately recognized
and dealt with.
2.1.2. Security Practices
For physical device security, equipment is kept in highly restrictive
environments. Only authorized users with cardkey badges have access
to any of the physical locations that contain critical network
infrastructure devices. These cardkey systems keep track of who
Kaeo Expires March 2, 2007 [Page 9]
Internet-Draft OPSEC Practices August 2006
accessed which location and at what time. Most cardkey systems have
a fail back "master key" in case the card system is down. This
"master key" usually has limited access and its use is also carefully
logged (which should only happen if the cardkey system is NOT online/
functional).
All console access is always password protected and the login time is
set to time out after a specified amount of inactivity - typically
between 3-10 minutes. The type of privileges that you obtain from a
console login varies between separate vendor devices. In some cases
you get initial basic access and need to perform a second
authentication step to get more privileged (i.e. enable or root)
access. In other vendors you get the more privileged access when you
log into the console as root, without requiring a second
authentication step.
How ISPs manage these logins vary greatly although many of the larger
ISPs employ some sort of AAA mechanism to help automate privilege
level authorization and can utilize the automation to bypass the need
for a second authentication step. Also, many ISPs define separate
classes of users to have different privileges while logged onto the
console. Typically all console access is provided via an out-of-band
(OOB) management infrastructure which is discussed in the section on
OOB management.
2.1.3. Security Services
The following security services are offered through the use of the
practices described in the previous section:
o User Authentication - All individuals who have access to the
physical facility are authenticated. Console access is
authenticated.
o User Authorization - An authenticated individual has implicit
authorization to perform commands on the device. In some cases
multiple authentication is required to differentiate between basic
and more privileged access.
o Data Origin Authentication - Not applicable
o Access Control - Not applicable
o Data Integrity - Not applicable
o Data Confidentiality - Not applicable
Kaeo Expires March 2, 2007 [Page 10]
Internet-Draft OPSEC Practices August 2006
o Auditing / Logging - All access to the physical locations of the
infrastructure equipment is logged via electronic card-key
systems. All console access is logged (refer to the OOB
management section for more details)
o DoS Mitigation - Not applicable
2.1.4. Additional Considerations
Physical security is relevant to operational security practices as
described in this document mostly from a console access perspective.
Most ISPs provide console access via an OOB management infrastructure
which is discussed in the OOB management section of this document.
The physical and logical authentication and logging systems should be
run independently of each other and reside in different physical
locations. These systems need to be secured to ensure that they
themselves will not be compromised which could give the intruder
valuable authentication and logging information.
Social engineering plays a big role in many physical access
compromises. Most ISPs have set up training classes and awareness
programs to educate company personnel to deny physical access to
people who are not properly authenticated or authorized to have
physical access to critical infrastructure devices.
2.2. Device Management - In-Band and Out-of-Band (OOB)
In-band management is generally considered to be device access where
the control traffic takes the same data path as the data which
traverses the network. Out-of-band management is generally
considered to be device access where the control traffic takes a
separate path as the data which traverses the network. In many
environments, device management for layer 2 and layer 3
infrastructure devices is deployed as part of an out-of-band
management infrastructure although there are some instances where it
is deployed in-band as well. Note that while many of the security
concerns and practices are the same for OOB management and in-band
management, most ISPs prefer an OOB management system since access to
the devices which make up this management network are more vigilantly
protected and considered to be less susceptible to malicious
activity.
Console access is always architected via an OOB network. Presently,
the mechanisms used for either in-band management or OOB are via
virtual terminal access (i.e. Telnet or SSH), SNMP, or HTTP. In all
large ISPs that were interviewed, HTTP management is never used and
is explicitly disabled. Note that file transfer protocols (TFTP,
Kaeo Expires March 2, 2007 [Page 11]
Internet-Draft OPSEC Practices August 2006
FTP, SCP) will be covered in the 'Software Upgrades and Configuration
Integrity/Validation' section.
2.2.1. Threats / Attacks
For device management, passive attacks are possible if someone has
the capability to intercept data between the management device and
the managed device. The threat is possible if a single
infrastructure device is somehow compromised and can act as a network
sniffer or if it is possible to insert a new device which acts as a
network sniffer.
Active attacks are possible for both on-path and off-path scenarios.
For on-path active attacks, the situation is the same as for a
passive attack, where either a device has to already be compromised
or a device can be inserted into the path. For off-path active
attacks, where a topology subversion is required to reroute traffic
and essentially bring the attacker on-path, the attack is generally
limited to message insertion or modification.
2.2.1.1. Confidentiality Violations
Confidentiality violations can occur when a miscreant intercepts any
management data that has been sent in cleartext or with weak
encryption. This includes interception of usernames and passwords
with which an intruder can obtain unauthorized access to network
devices. It can also include other information such as logging or
configuration information if an administrator is remotely viewing
local logfiles or configuration information.
2.2.1.2. Offline Cryptographic Attacks
If username/password information was encrypted but the cryptographic
mechanism used made it easy to capture data and break the encryption
key, the device management traffic could be compromised. The traffic
would need to be captured either by eavesdropping on the network or
by being able to divert traffic to a malicious user.
2.2.1.3. Replay Attacks
For a replay attack to be successful, the management traffic would
need to first be captured either on-path or diverted to an attacker
to later be replayed to the intended recipient.
2.2.1.4. Message Insertion/Deletion/Modification
Data can be manipulated by someone in control of intermediary hosts.
Forging data is also possible with IP spoofing, where a remote host
Kaeo Expires March 2, 2007 [Page 12]
Internet-Draft OPSEC Practices August 2006
sends out packets which appear to come from another, trusted host.
2.2.1.5. Man-In-The-Middle
A man-in-the-middle attack attacks the identity of a communicating
peer rather than the data stream itself. The attacker intercepts
traffic that is sent from a management system to the networking
infrastructure device and traffic that is sent from the network
infrastructure device to the management system.
2.2.2. Security Practices
OOB management is done via a terminal server at each location. SSH
access is used to get to the terminal server from where sessions to
the devices are initiated. Dial-in access is deployed as a backup if
the network is not available however, it is common to use dial-back,
encrypting modems and/or one-time-password (OTP) modems to avoid the
security weaknesses of plain dial-in access.
All in-band management and OOB management access to layer 2 and layer
3 devices is authenticated. The user authentication and
authorization is typically controlled by a AAA server (i.e. RADIUS
and/or TACACS+). Credentials used to determine the identity of the
user vary from static username/password to one-time username/password
scheme such as Secure-ID. Static username/passwords are expired
after a specified period of time, usually 30 days. Every
authenticated entity via AAA is an individual user for greater
granularity of control. Note that often the AAA server used for OOB
management authentication is a separate physical device from the AAA
server used for in-band management user authentication. In some
deployments, the AAA servers used for device management
authentication/authorization/accounting are on separate networks to
provide a demarcation for any other authentication functions.
For backup purposes, there is often a single local database entry for
authentication which is known to a very limited set of key personnel.
It is usually the highest privilege level username/password
combination, which in most cases is the same across all devices.
This local device password is routinely regenerated once every 2-3
months and is also regenerated immediately after an employee who had
access to that password leaves the company or is no longer authorized
to have knowledge of that password.
Each individual user in the AAA database is configured with specific
authorization capability. Specific commands are either individually
denied or permitted depending on the capability of the device to be
accessed. Multiple privilege levels are deployed. Most individuals
are authorized with basic authorization to perform a minimal set of
Kaeo Expires March 2, 2007 [Page 13]
Internet-Draft OPSEC Practices August 2006
commands while a subset of individuals are authorized to perform more
privileged commands. Securing the AAA server is imperative and
access to the AAA server itself is strictly controlled. When an
individual leaves the company, his/her AAA account is immediately
deleted and the TACACS/RADIUS shared secret is reset for all devices.
Some management functions are performed using command line interface
(CLI) scripting. In these scenarios, a dedicated user is used for
the identity in scripts that perform CLI scripting. Once
authenticated, these scripts control which commands are legitimate
depending on authorization rights of the authenticated individual.
SSH is always used for virtual terminal access to provide for an
encrypted communication channel. There are exceptions due to
equipment limitations which are described in the additional
considerations section.
If SNMP is used for management, it is for read queries only and
restricted to specific hosts. If possible, the view is also
restricted to only send the information that the management station
needs rather than expose the entire configuration file with the read-
only SNMP community. The community strings are carefully chosen to
be difficult to crack and there are procedures in place to change
these community strings between 30-90 days. If systems support two
SNMP community strings, the old string is replaced by first
configuring a second newer community string and then migrating over
from the currently used string to the newer one. Most large ISPs
have multiple SNMP systems accessing their routers so it takes more
then one maintenance period to get all the strings fixed in all the
right systems. SNMP RW is not used and is disabled by configuration.
Access control is strictly enforced for infrastructure devices by
using stringent filtering rules. A limited set of IP addresses are
allowed to initiate connections to the infrastructure devices and are
specific to the services which they are to limited to (i.e. SSH and
SNMP).
All device management access is audited and any violations trigger
alarms which initiate automated email, pager and/or telephone
notifications. AAA servers keeps track of the authenticated entity
as well as all the commands that were carried out on a specific
device. Additionally, the device itself logs any access control
violations (i.e. if an SSH request comes in from an IP address which
is not explicitly permitted, that event is logged so that the
offending IP address can be tracked down and investigations made as
to why it was trying to access a particular infrastructure device)
Kaeo Expires March 2, 2007 [Page 14]
Internet-Draft OPSEC Practices August 2006
2.2.3. Security Services
The security services offered for device OOB management are nearly
identical to those of device in-band management. Due to the critical
nature of controlling and limiting device access, many ISPs feel that
physically separating the management traffic from the normal customer
data traffic will provide an added level of risk mitigation and limit
the potential attack vectors. The following security services are
offered through the use of the practices described in the previous
section:
o User Authentication - All individuals are authenticated via AAA
services.
o User Authorization - All individuals are authorized via AAA
services to perform specific operations once successfully
authenticated.
o Data Origin Authentication - Management traffic is strictly
filtered to allow only specific IP addresses to have access to the
infrastructure devices. This does not alleviate risk from spoofed
traffic, although when combined with edge filtering using BCP38
[RFC2827] and BCP84 [RFC3704] guidelines (discussed in the section
2.5), then the risk of spoofing is mitigated barring a compromised
internal system. Also, using SSH for device access ensures that
noone can spoof the traffic during the SSH session.
o Access Control - Management traffic is filtered to allow only
specific IP addresses to have access to the infrastructure
devices.
o Data Integrity - Using SSH provides data integrity and ensures
that no one has altered the management data in transit.
o Data Confidentiality - Using SSH provides data confidentiality.
o Auditing / Logging - Using AAA provides an audit trail for who
accessed which device and which operations were performed.
o DoS Mitigation - Using packet filters to allow only specific IP
addresses to have access to the infrastructure devices. This
limits but does not prevent spoofed DoS attacks directed at an
infrastructure device. However, the risk is lowered by using a
separate physical network for management purposes.
Kaeo Expires March 2, 2007 [Page 15]
Internet-Draft OPSEC Practices August 2006
2.2.4. Additional Considerations
Password selection for any device management protocol used is
critical to ensure that the passwords are hard to guess or break
using a brute-force attack.
IPsec is considered too difficult to deploy and the common protocol
to provide for confidential management access is SSH. There are
exceptions for using SSH due to equipment limitations since SSH may
not be supported on legacy equipment. In some cases changing the
hostname of a device requires an SSH rekey event since the key is
based on some combination of host name, MAC address and time. Also,
in the case where the SSH key is stored on a route processor card, a
re-keying of SSH would be required whenever the route processor card
needs to be swapped. Some providers feel that this operational
impact exceeds the security necessary and instead use Telnet from
trusted inside hosts (called 'jumphosts' or 'bastion hosts') to
manage those devices. An individual would first SSH to the jumphost
and then Telnet from the jumphost to the actual infrastructure
device, fully understanding that any passwords will be sent in the
clear between the jumphost and the device it is connecting to. All
authentication and authorization is still carried out using AAA
servers.
In instances where Telnet access is used, the logs on the AAA servers
are more verbose and more attention is paid to them to detect any
abnormal behavior. The jumphosts themselves are carefully controlled
machines and usually have limited access. Note that Telnet is NEVER
allowed to an infrastructure device except from specific jumphosts;
i.e. packet filters are used at the console server and/or
infrastructure device to ensure that Telnet is only allowed from
specific IP addresses.
With thousands of devices to manage, some ISPs have created automated
mechanisms to authenticate to devices. As an example, Kerberos has
been used to automate the authentication process for devices that
have support for Kerberos. An individual would first log in to a
Kerberized UNIX server using SSH and generate a Kerberos 'ticket'.
This 'ticket' is generally set to have a lifespan of 10 hours and is
used to automatically authenticate the individual to the
infrastructure devices.
In instances where SNMP is used, some legacy devices only support
SNMPv1 which then requires the provider to mandate its use across all
infrastructure devices for operational simplicity. SNMPv2 is
primarily deployed since it is easier to set up than v3.
Kaeo Expires March 2, 2007 [Page 16]
Internet-Draft OPSEC Practices August 2006
2.3. Data Path
This section refers to how traffic is handled which traverses the
network infrastructure device. The primary goal of ISPs is to
forward customer traffic. However, due to the large amount of
malicious traffic that can cause DoS attacks and render the network
unavailable, specific measures are sometimes deployed to ensure the
availability to forward legitimate customer traffic.
2.3.1. Threats / Attacks
Any data traffic can potentially be attack traffic and the challenge
is to detect and potentially stop forwarding any of the malicious
traffic. The deliberately sourced attack traffic can consist of
packets with spoofed source and/or destination addresses or any other
malformed packet which mangle any portion of a header field to cause
protocol-related security issues (such as resetting connections,
causing unwelcome ICMP redirects, creating unwelcome IP options or
packet fragmentations).
2.3.2. Security Practices
Filtering and rate limiting are the primary mechanism to provide risk
mitigation of malicious traffic rendering the ISP services
unavailable. However, filtering and rate limiting of data path
traffic is deployed in a variety of ways depending on how automated
the process is and what the capabilities and performance limitations
of existing deployed hardware are.
The ISPs which do not have performance issues with their equipment
follow BCP38 [RFC2827] and BCP84 [RFC3704] guidelines for ingress
filtering. BCP38 recommends filtering ingress packets with obviously
spoofed and/or 'reserved' source addresses to limit the effects of
denial of service attacks while BCP84 extends the recommendation for
multi-homed environments. Filters are also used to help alleviate
issues between service providers. Without any filtering, an inter-
exchange peer could steal transit just by using static routes and
essentially redirect data traffic. Therefore, some ISPs have
implemented ingress/egress filters which block unexpected source and
destination addresses not defined in the above-mentioned documents.
Null routes and black-hole triggered routing [RFC3882] are used to
deter any detected malicious traffic streams. These two techniques
are described in more detail in section 2.8 below.
Most ISPs consider layer 4 filtering useful but it is only
implemented if performance limitations allow for it. Layer 4
filtering is typically only when no other option exists since it does
pose a large administrative overhead and ISPs are very much opposed
Kaeo Expires March 2, 2007 [Page 17]
Internet-Draft OPSEC Practices August 2006
to acting as the Internet firewall. Netflow is used for tracking
traffic flows but there is some concern whether sampling is good
enough to detect malicious behavior.
Unicast RPF is not consistently implemented. Some ISPs are in
process of doing so while other ISPs think that the perceived benefit
of knowing that spoofed traffic comes from legitimate addresses are
not worth the operational complexity. Some providers have a policy
of implementing uRPF at link speeds of DS3 and below which was due to
the fact that all hardware in the network supported uRPF for DS3
speeds and below. At higher speed links the uRPF support was
inconsistent and it was easier for operational people to implement a
consistent solution.
2.3.3. Security Services
o User Authentication - Not applicable
o User Authorization - Not applicable
o Data Origin Authentication - When IP address filtering per BCP38,
BCP84 and uRPF are deployed at network edges it can ensure that
any spoofed traffic comes from at least a legitimate IP address
and can be tracked.
o Access Control - IP address filtering and layer 4 filtering is
used to deny forbidden protocols and limit traffic destined for
infrastructure device itself. Filters are also used to block
unexpected source/destination addresses.
o Data Integrity - Not applicable
o Data Confidentiality - Not applicable
o Auditing / Logging - Filtering exceptions are logged for potential
attack traffic.
o DoS Mitigation - Black-hole triggered filtering and rate-limiting
are used to limit the risk of DoS attacks.
2.3.4. Additional Considerations
For layer 2 devices, MAC address filtering and authentication is not
used in large-scale deployments. This is due to the problems it can
cause when troubleshooting networking issues. Port security becomes
unmanageable at a large scale where 1000s of switches are deployed.
Kaeo Expires March 2, 2007 [Page 18]
Internet-Draft OPSEC Practices August 2006
Rate limiting is used by some ISPs although other ISPs believe it is
not really useful since attackers are not well behaved and it doesn't
provide any operational benefit over the complexity. Some ISPs feel
that rate limiting can also make an attacker's job easier by
requiring the attacker to send less traffic to starve legitimate
traffic that is part of a rate limiting scheme. Rate limiting may be
improved by developing flow-based rate-limiting capabilities with
filtering hooks. This would improve the performance as well as the
granularity over current capabilities.
Lack of consistency regarding the ability to filter, especially with
respect to performance issues cause some ISPs to not implement BCP38
and BCP84 guidelines for ingress filtering. One such example is at
edge boxes where you have up to 1000 T1's connecting into a router
with an OC-12 uplink. Some deployed devices experience a large
performance impact with filtering which is unacceptable for passing
customer traffic through, though ingress filtering (uRPF) might be
applicable at the devices connecting these aggregation routers.
Where performance is not an issue, the ISPs make a tradeoff between
management versus risk.
2.4. Routing Control Plane
The routing control plane deals with all the traffic which is part of
establishing and maintaining routing protocol information.
2.4.1. Threats / Attacks
Attacks on the routing control plane can be both from passive or
active sources. Passive attacks are possible if someone has the
capability to intercept data between the communicating routing peers.
This can be accomplished if a single routing peer is somehow
compromised and can act as a network sniffer or if it is possible to
insert a new device which acts as a network sniffer.
Active attacks are possible for both on-path and off-path scenarios.
For on-path active attacks, the situation is the same as for a
passive attack, where either a device has to already be compromised
or a device can be inserted into the path. This may lead to an
attacker impersonating a legitimate routing peer and exchanging
routing information. Unintentional active attacks are more common
due to configuration errors, which cause legitimate routing peers to
feed invalid routing information to other neighboring peers.
For off-path active attacks, the attacks are generally limited to
message insertion or modification which can divert traffic to
illegitimate destinations and cause traffic to never reach its
intended destination.
Kaeo Expires March 2, 2007 [Page 19]
Internet-Draft OPSEC Practices August 2006
2.4.1.1. Confidentiality Violations
Confidentiality violations can occur when a miscreant intercepts any
of the routing update traffic. This is becoming more of a concern
because many ISPs are classifying addressing schemes and network
topologies as private and proprietary information. It is also a
concern because the routing protocol packets contain information that
may show ways in which routing sessions could be spoofed or hijacked.
This in turn could lead into a man-in-the-middle attack where the
miscreants can insert themselves into the traffic path or divert the
traffic path and violate the confidentiality of user data.
2.4.1.2. Offline Cryptographic Attacks
If any cryptographic mechanism was used to provide for data integrity
and confidentiality, an offline cryptographic attack could
potentially compromise the data. The traffic would need to be
captured either by eavesdropping on the network or by being able to
divert traffic to a malicious user. Note that by using
cryptographically protected routing information, the latter would
require the cryptographic key to already be compromised anyway so
this attack is only feasible if a device was able eavesdrop and
capture the cryptographically protected routing information.
2.4.1.3. Replay Attacks
For a replay attack to be successful, the routing control plane
traffic would need to first be captured either on-path or diverted to
an attacker to later be replayed to the intended recipient.
Additionally, since many of these protocols include replay protection
mechanisms, these would also need to be subverted if applicable.
2.4.1.4. Message Insertion/Deletion/Modification
Routing control plane traffic can be manipulated by someone in
control of intermediate hosts. In addition, traffic can be injected
by forging IP addresses, where a remote router sends out packets
which appear to come from another, trusted router. If enough traffic
is injected to be processed by limited memory routers it can cause a
DoS attack.
2.4.1.5. Man-In-The-Middle
A man-in-the-middle attack attacks the identity of a communicating
peer rather than the data stream itself. The attacker intercepts
traffic that is sent from one routing peer to the other and
communicates on behalf of one of the peers. This can lead to
diversion of the user traffic to either an unauthorized receiving
Kaeo Expires March 2, 2007 [Page 20]
Internet-Draft OPSEC Practices August 2006
party or cause legitimate traffic to never reach its intended
destination.
2.4.2. Security Practices
Securing the routing control plane takes many features which are
generally deployed as a system. MD5 authentication is used by some
ISPs to validate the sending peer and to ensure that the data in
transit has not been altered. Some ISPs only deploy MD5
authentication at customer's request. Additional sanity checks to
ensure with reasonable certainty that the received routing update was
originated by a valid routing peer include route filters and the
Generalized TTL Security Mechanism (GTSM) feature [RFC3682]
(sometimes also referred to as the TTL-Hack). The GTSM feature is
used for protocols such as BGP and makes use of a packet's Time To
Live (TTL) field (IPv4) or Hop Limit (IPv6) to protect communicating
peers. If GTSM is used, it is typically only deployed in limited
scenarios between internal BGP peers due to lack of consistent
support between vendor products and operating system versions.
Packet filters are used to limit which systems can appear as a valid
peer while route filters are used to limit which routes are believed
from a valid peer. In the case of BGP routing, a variety of policies
are deployed to limit the propagation of invalid routing information.
These include: incoming and outgoing prefix filters for BGP
customers, incoming and outgoing prefix filters for peers and
upstream neighbors, incoming AS-PATH filter for BGP customers,
outgoing AS-PATH filter towards peers and upstream neighbors, route
dampening and rejecting selected attributes and communities.
Consistency between these policies varies greatly and there is a
definite distinction whether the other end is an end-site vs an
internal peer vs another big ISP or customer. Mostly ISPs do prefix-
filter their end-site customers but due to the operational
constraints of maintaining large prefix filter lists, many ISPs are
starting to depend on BGP AS-PATH filters to/from their peers and
upstream neighbors.
In cases where prefix lists are not used, operators often define a
maximum prefix limit per peer to prevent misconfiguration (e.g.,
unintentional de-aggregation or neighbor routing policy mis-
configuration) or overload attacks. ISPs need to coordinate between
each other what the expected prefix exchange is, and increase this
number by some sane amount. It is important for ISPs to pad the max-
prefix number enough to allow for valid swings in routing
announcements to prevent an unintentional shutting down of the BGP
session. Individual implementation amongst ISPs are unique, and
depending on equipment supplier(s) different implementation options
are available. Most equipment vendors offer implementation options
Kaeo Expires March 2, 2007 [Page 21]
Internet-Draft OPSEC Practices August 2006
ranging from just logging excessive prefixes being received to
automatically shutting down the session. If the option of
reestablishing a session after some pre-configured idle timeout has
been reached is available, it should be understood that automatically
reestablishing the session may potentially introduce instability
continuously into the overall routing table if a policy mis-
configuration on the adjacent neighbor is causing the condition. If
a serious mis-configuration on a peering neighbor has occurred then
automatically shutting down the session and leaving it shut down
until being manually cleared is sometimes best and allows for
operator intervention to correct as needed.
Some large ISPs require that routes be registered in an Internet
Routing Registry [IRR] which can then be part of the RADB - a public
registry of routing information for networks in the Internet that can
be used to generate filter lists. Some ISPs, especially in europe,
require registered routes before agreeing to become an eBGP peer with
someone.
Many ISPs also do not propagate interface IP addresses to further
reduce attack vectors on routers and connected customers.
2.4.3. Security Services
o User Authentication - Not applicable
o User Authorization - Not applicable
o Data Origin Authentication - By using MD5 authentication and/or
the TTL-hack a routing peer can be reasonably certain that traffic
originated from a valid peer.
o Access Control - Route filters, AS-PATH filters and prefix limits
are used to control access to specific parts of the network.
o Data Integrity - By using MD5 authentication a peer can be
reasonably certain that the data has not been modified in transit
but there is no mechanism to prove the validity of the routing
information itself.
o Data Confidentiality - Not implemented
o Auditing / Logging - Filter exceptions are logged.
o DoS Mitigation - Many DoS attacks are mitigated using a
combination of techniques including: MD5 authentication, the GTSM
feature, filtering routing advertisements to bogons and filtering
Kaeo Expires March 2, 2007 [Page 22]
Internet-Draft OPSEC Practices August 2006
routing advertisements to one's own network.
2.4.4. Additional Considerations
So far the primary concern to secure the routing control plane has
been to validate the sending peer and to ensure that the data in
transit has not been altered. Although MD5 routing protocol
extensions have been implemented which can provide both services,
they are not consistently deployed amongst ISPs. Two major
deployment concerns have been implementation issues where both
software bugs and the lack of graceful re-keying options have caused
significant network down times. Also, some ISPs express concern that
deploying MD5 authentication will itself be a worse DoS attack victim
and prefer to use a combination of other risk mitigation mechanisms
such as GTSM (for BGP) and route filters. An issue with GTSM is that
it is not supported on all devices across different vendors
products'.
IPsec is not deployed since the operational management aspects of
ensuring interoperability and reliable configurations is too complex
and time consuming to be operationally viable. There is also limited
concern to the confidentiality of the routing information. The
integrity and validity of the updates are of much greater concern.
There is concern for manual or automated actions which introduce new
routes and can affect the entire routing domain.
2.5. Software Upgrades and Configuration Integrity / Validation
Software upgrades and configuration changes are usually performed as
part of either in-band or OOB management functions. However, there
are additional considerations to be taken into account which are
enumerated in this section.
2.5.1. Threats / Attacks
Attacks performed on system software and configurations can be both
from passive or active sources. Passive attacks are possible if
someone has the capability to intercept data between the network
infrastructure device and the system which is downloading or
uploading the software or configuration information. This can be
accomplished if a single infrastructure device is somehow compromised
and can act as a network sniffer or if it is possible to insert a new
device which acts as a network sniffer.
Active attacks are possible for both on-path and off-path scenarios.
For on-path active attacks, the situation is the same as for a
passive attack, where either a device has to already be compromised
Kaeo Expires March 2, 2007 [Page 23]
Internet-Draft OPSEC Practices August 2006
or a device can be inserted into the path. For off-path active
attacks, the attacks are generally limited to message insertion or
modification where the attacker may wish to load illegal software or
configuration files to an infrastructure device.
Note that similar issues are relevant when software updates are
downloaded from a vendor site to an ISPs network management system
that is responsible for software updates and/or configuration
information.
2.5.1.1. Confidentiality Violations
Confidentiality violations can occur when a miscreant intercepts any
of the software image or configuration information. The software
image may give an indication of exploits which the device is
vulnerable to while the configuration information can inadvertently
lead attackers to identify critical infrastructure IP addresses and
passwords.
2.5.1.2. Offline Cryptographic Attacks
If any cryptographic mechanism was used to provide for data integrity
and confidentiality, an offline cryptographic attack could
potentially compromise the data. The traffic would need to be
captured either by eavesdropping on the communication path or by
being able to divert traffic to a malicious user.
2.5.1.3. Replay Attacks
For a replay attack to be successful, the software image or
configuration file would need to first be captured either on-path or
diverted to an attacker to later be replayed to the intended
recipient. Additionally, since many protocols do have replay
protection capabilities, these would have to be subverted as well in
applicable situations.
2.5.1.4. Message Insertion/Deletion/Modification
Software images and configuration files can be manipulated by someone
in control of intermediate hosts. By forging an IP address and
impersonating a valid host which can download software images or
configuration files, invalid files can be downloaded to an
infrastructure device. This can also be the case from trusted
vendors who may unbeknownst to them have compromised trusted hosts.
An invalid software image or configuration file can cause a device to
hang and become inoperable. Spoofed configuration files can be hard
to detect, especially when the only added command is to allow a
miscreant access to that device by entering a filter allowing a
Kaeo Expires March 2, 2007 [Page 24]
Internet-Draft OPSEC Practices August 2006
specific host access and configuring a local username/password
database entry for authentication to that device.
2.5.1.5. Man-In-The-Middle
A man-in-the-middle attack attacks the identity of a communicating
peer rather than the data stream itself. The attacker intercepts
traffic that is sent between the infrastructure device and the host
used to upload/download the system image or configuration file. He/
she can then act on behalf of one or both of these systems.
If an attacker obtained a copy of the software image being deployed,
he could potentially exploit a known vulnerability and gain access to
the system. From a captured configuration file, he could obtain
confidential network topology information or even more damaging
information if any of the passwords in the configuration file were
not encrypted.
2.5.2. Security Practices
Images and configurations are stored on specific hosts which have
limited access. All access and activity relating to these hosts are
authenticated and logged via AAA services. When uploaded/downloading
any system software or configuration files, either TFTP, FTP or SCP
can be used. Where possible, SCP is used to secure the data transfer
and FTP is generally never used. All SCP access is username/password
authenticated but since this requires an interactive shell, most ISPs
will use shared key authentication to avoid the interactive shell.
While TFTP access does not have any security measures, it is still
widely used especially in OOB management scenarios. Some ISPs
implement IP-based restriction on the TFTP server while some custom
written TFTP servers will support MAC-based authentication. The MAC-
based authentication is more common when using TFTP to bootstrap
routers remotely.
In most environments scripts are used for maintaining the images and
configurations of a large number of routers. To ensure the integrity
of the configurations, every hour the configuration files are polled
and compared to the previously polled version to find discrepancies.
In at least one environment these tools are Kerberized to take
advantage of automated authentication (not confidentiality).
'Rancid' is one popular publicly available tool for detecting
configuration and system changes.
Filters are used to limit access to uploading/downloading
configuration files and system images to specific IP addresses and
protocols.
Kaeo Expires March 2, 2007 [Page 25]
Internet-Draft OPSEC Practices August 2006
The software images perform CRC-checks and the system binaries use
the MD5 algorithm to validate integrity. Many ISPs expressed
interest in having software image integrity validation based on the
MD5 algorithm for enhanced security.
In all configuration files, most passwords are stored in an encrypted
format. Note that the encryption techniques used in varying products
can vary and that some weaker encryption schemes may be subject to
off-line dictionary attacks. This includes passwords for user
authentication, MD5-authentication shared secrets, AAA server shared
secrets, NTP shared secrets, etc. For older software which may not
support this functionality, configuration files may contain some
passwords in readable format. Most ISPs mitigate any risk of
password compromise by either storing these configuration files
without the password lines or by requiring authenticated and
authorized access to the configuration files which are stored on
protected OOB management devices.
Automated security validation is performed on infrastructure devices
using nmap and nessus to ensure valid configuration against many of
the well-known attacks.
2.5.3. Security Services
o User Authentication - All users are authenticated before being
able to download/upload any system images or configuration files.
o User Authorization - All authenticated users are granted specific
privileges to download or upload system images and/or
configuration files.
o Data Origin Authentication - Filters are used to limit access to
uploading/downloading configuration files and system images to
specific IP addresses.
o Access Control - Filters are used to limit access to uploading/
downloading configuration files and system images to specific IP
addresses and protocols.
o Data Integrity - All systems use either a CRC-check or MD5
authentication to ensure data integrity. Also tools such as
rancid are used to automatically detect configuration changes.
o Data Confidentiality - If the SCP protocol is used then there is
confidentiality of the downloaded/uploaded configuration files and
system images.
Kaeo Expires March 2, 2007 [Page 26]
Internet-Draft OPSEC Practices August 2006
o Auditing / Logging - All access and activity relating to
downloading/uploading system images and configuration files are
logged via AAA services and filter exception rules.
o DoS Mitigation - A combination of filtering and CRC-check / MD5-
based integrity checks are used to mitigate the risks of DoS
attacks. If the software updates and configuration changes are
performed via an OOB management system, this is also added
protection.
2.5.4. Additional Considerations
Where the MD5 algorithm is not used to perform data integrity
checking of software images and configuration files, ISPs have
expressed an interest in having this functionality. IPsec is
considered too cumbersome and operationally difficult to use for data
integrity and confidentiality.
2.6. Logging Considerations
Although logging is part of all the previous sections, it is
important enough to be covered as a separate item. The main issues
revolve around what gets logged, how long are logs kept and what
mechanisms are used to secure the logged information while it is in
transit and while it is stored.
2.6.1. Threats / Attacks
Attacks on the logged data can be both from passive or active
sources. Passive attacks are possible if someone has the capability
to intercept data between the recipient logging server and the device
the logged data originated from. This can be accomplished if a
single infrastructure device is somehow compromised and can act as a
network sniffer or if it is possible to insert a new device which
acts as a network sniffer.
Active attacks are possible for both on-path and off-path scenarios.
For on-path active attacks, the situation is the same as for a
passive attack, where either a device has to already be compromised
or a device can be inserted into the path. For off-path active
attacks, the attacks are generally limited to message insertion or
modification which can alter the logged data to keep any compromise
from being detected or to destroy any evidence which could be used
for criminal prosecution.
Kaeo Expires March 2, 2007 [Page 27]
Internet-Draft OPSEC Practices August 2006
2.6.1.1. Confidentiality Violations
Confidentiality violations can occur when a miscreant intercepts any
of the logging data which is in transit on the network. This could
lead to privacy violations if some of the logged data has not been
sanitized to disallow any data that could be a violation of privacy
to be included in the logged data.
2.6.1.2. Offline Cryptographic Attacks
If any cryptographic mechanism was used to provide for data integrity
and confidentiality, an offline cryptographic attack could
potentially compromise the data. The traffic would need to be
captured either by eavesdropping on the network or by being able to
divert traffic to a malicious user.
2.6.1.3. Replay Attacks
For a replay attack to be successful, the logging data would need to
first be captured either on-path or diverted to an attacker and later
replayed to the recipient.
2.6.1.4. Message Insertion/Deletion/Modification
Logging data could be injected, deleted or modified by someone in
control of intermediate hosts. Logging data can also be injected by
forging packets from either legitimate or illegitimate IP addresses.
2.6.1.5. Man-In-The-Middle
A man-in-the-middle attack attacks the identity of a communicating
peer rather than the data stream itself. The attacker intercepts
traffic that is sent between the infrastructure device and the
logging server or traffic sent between the logging server and the
database which is used to archive the logged data. Any unauthorized
access to logging information could lead to knowledge of private and
proprietary network topology information which could be used to
compromise portions of the network. An additional concern is having
access to logging information which could be deleted or modified so
as to cover any traces of a security breach.
2.6.2. Security Practices
Logging is mostly performed on an exception auditing basis when it
comes to filtering (i.e. traffic which is NOT allowed is logged).
This is to assure that the logging servers are not overwhelmed with
data which would render most logs unusable. Typically the data
logged will contain the source and destination IP addresses and layer
Kaeo Expires March 2, 2007 [Page 28]
Internet-Draft OPSEC Practices August 2006
4 port numbers as well as a timestamp. The syslog protocol is used
to transfer the logged data between the infrastructure device to the
syslog server. Many ISPs use the OOB management network to transfer
syslog data since there is virtually no security performed between
the syslog server and the device. All ISPs have multiple syslog
servers - some ISPs choose to use separate syslog servers for varying
infrastructure devices (i.e. one syslog server for backbone routers,
one syslog server for customer edge routers, etc.)
The timestamp is derived from NTP which is generally configured as a
flat hierarchy at stratum1 and stratum2 to have less configuration
and less maintenance. Consistency of configuration and redundancy is
the primary goal. Each router is configured with several stratum1
server sources, which are chosen to ensure that proper NTP time is
available even in the event of varying network outages.
In addition to logging filtering exceptions, the following is
typically logged: Routing protocol state changes, all device access
(regardless of authentication success or failure), all commands
issued to a device, all configuration changes and all router events
(boot-up/flaps).
The main function of any of these log messages is to see what the
device is doing as well as to try and ascertain what certain
malicious attackers are trying to do. Since syslog is an unreliable
protocol, when routers boot or lose adjacencies, not all messages
will get delivered to the remote syslog server. Some vendors may
implement syslog buffering (e.g., buffer the messages until you have
a route to the syslog destination) but this is not standard.
Therefore, operators often have to look at local syslog information
on a device (which typically has very little memory allocated to it)
to make up for the fact that the server-based syslog files can be
incomplete. Some ISPs also put in passive devices to see routing
updates and withdrawals and do not rely solely on the device for log
files. This provides a backup mechanism to see what is going on in
the network in the event that a device may 'forget' to do syslog if
the CPU is busy.
The logs from the various syslog server devices are generally
transferred into databases at a set interval which can be anywhere
from every 10 minutes to every hour. One ISP uses Rsync to push the
data into a database and then the information is sorted manually by
someone SSH'ing to that database.
2.6.3. Security Services
Kaeo Expires March 2, 2007 [Page 29]
Internet-Draft OPSEC Practices August 2006
o User Authentication - Not applicable
o User Authorization - Not applicable
o Data Origin Authentication - Not implemented
o Access Control - Filtering on logging host and server IP address
to ensure that syslog information only goes to specific syslog
hosts.
o Data Integrity - Not implemented
o Data Confidentiality - Not implemented
o Auditing / Logging - This entire section deals with logging.
o DoS Mitigation - An OOB management system is used and sometimes
different syslog servers are used for logging information from
varying equipment. Exception logging tries to keep information to
a minimum.
2.6.4. Additional Considerations
There is no security with syslog and ISPs are fully cognizant of
this. IPsec is considered too operationally expensive and cumbersome
to deploy. Syslog-ng and stunnel are being looked at for providing
better authenticated and integrity protected solutions. Mechanisms
to prevent unauthorized personnel from tampering with logs is
constrained to auditing who has access to the logging servers and
files.
ISPs expressed requirements for more than just UDP syslog.
Additionally, they would like more granular and flexible facilities
and priorities, i.e. specific logs to specific servers. Also, a
common format for reporting standard events so that they don't have
to modify parsers after each upgrade of vendor device or software.
2.7. Filtering Considerations
Although filtering has been covered under many of the previous
sections, this section will provide some more insights to the
filtering considerations that are currently being taken into account.
Filtering is now being categorized into three specific areas: data
plane, management plane and routing control plane.
Kaeo Expires March 2, 2007 [Page 30]
Internet-Draft OPSEC Practices August 2006
2.7.1. Data Plane Filtering
Data plane filters control the traffic that traverses through a
device and affect transit traffic. Most ISPs deploy these kinds of
filters at the customer facing edge devices to mitigate spoofing
attacks using BCP38 and BCP84 guidelines.
2.7.2. Management Plane Filtering
Management filters control the traffic to and from a device. All of
the protocols which are used for device management fall under this
category and includes SSH, Telnet, SNMP, NTP, HTTP, DNS, TFTP, FTP,
SCP and Syslog. This type of traffic is often filtered per interface
and is based on any combination of protocol, source and destination
IP address and source and destination port number. Some devices
support functionality to apply management filters to the device
rather than to the specific interfaces (e.g. receive ACL or loopback
interface ACL) which is gaining wider acceptance. Note that logging
the filtering rules can today place a burden on many systems and more
granularity is often required to more specifically log the required
exceptions.
Any services that are not specifically used are turned off.
IPv6 networks require the use of specific ICMP messages for proper
protocol operation. Therefore, ICMP cannot be completely filtered to
and from a device. Instead, granular ICMPv6 filtering is always
deployed to allow for specific ICMPv6 types to be sourced or destined
to a network device. A good guideline for IPv6 filtering is in the
draft work in progress on Recommendations for Filtering ICMPv6
Messages in Firewalls [I-D.ietf-v6ops-icmpv6-filtering-recs].
2.7.3. Routing Control Plane Filtering
Routing filters are used to control the flow of routing information.
In IPv6 networks, some providers are liberal in accepting /48s due to
the still unresolved multihoming issues while others filter at
allocation boundaries which are typically at /32. Any announcement
received that is longer than a /48 for IPv6 routing and a /24 for
IPv4 routing is filtered out of eBGP. Note that this is for non-
customer traffic. Most ISPs will accept any agreed upon prefix
length from its customer(s).
2.8. Denial of Service Tracking / Tracing
Denial of Service attacks are an ever increasing problem and require
vast amounts of resources to combat effectively. Some large ISPs do
not concern themselves with attack streams that are less than 1G in
Kaeo Expires March 2, 2007 [Page 31]
Internet-Draft OPSEC Practices August 2006
bandwidth - this is on the larger pipes where 1G is essentially less
than 5% of offered load. This is largely due to the large amounts of
DDoS traffic which continually requires investigation and mitigation.
At last count the number of hosts making up large distributed DoS
botnets exceeded 1 million hosts.
New techniques are continually evolving to automate the process of
detecting DoS sources and mitigating any adverse effects as quickly
as possible. At this time, ISPs are using a variety of mitigation
techniques including: sink hole routing, black-hole triggered
routing, uRPF, rate limiting and specific control plane traffic
enhancements. Each of these techniques will be detailed below.
2.8.1. Sink Hole Routing
Sink hole routing refers to injecting a more specific route for any
known attack traffic which will ensure that the malicious traffic is
redirected to a valid device or specific system where it can be
analyzed.
2.8.2. Black-Hole Triggered Routing
Black-hole triggered routing (also referred to as Remote Triggered
Black Hole Filtering) is a technique where the BGP routing protocol
is used to propagate routes which in turn redirects attack traffic to
the null interface where it is effectively dropped. This technique
is often used in large routing infrastructures since BGP can
propagate the information in a fast effective manner as opposed to
using any packet-based filtering techniques on hundreds or thousands
of routers. [refer to the following NANOG presentation for a more
complete description http://www.nanog.org/mtg-0402/pdf/morrow.pdf]
Note that this black-holing technique may actually fulfill the goal
of the attacker if the goal was to instigate blackholing traffic
which appeared to come from a certain site. On the other hand, this
blackhole technique can decrease the collateral damage caused by an
overly large attack aimed at something other than critical services.
2.8.3. Unicast Reverse Path Forwarding
Unicast Reverse Path Forwarding (uRPF) is a mechanism for validating
whether an incoming packet has a legitimate source address or not.
It has two modes: strict mode and loose mode. In strict mode, uRPF
checks whether the incoming packet has a source address that matches
a prefix in the routing table, and whether the interface expects to
receive a packet with this source address prefix. If the incoming
packet fails the unicast RPF check, the packet is not accepted on the
incoming interface. Loose mode uRPF is not as specific and the
Kaeo Expires March 2, 2007 [Page 32]
Internet-Draft OPSEC Practices August 2006
incoming packet is accepted if there is any route in the routing
table for the source address.
While BCP84 [RFC3704] and a study on uRPF experiences
[I-D.savola-bcp84-urpf-experiences] detail how asymmetry, i.e.
multiple routes to the source of a packet, does not preclude applying
feasible paths strict uRPF, it is generally not used on interfaces
that are likely to have routing asymmetry. Usually for the larger
ISPs, uRPF is placed at the customer edge of a network.
2.8.4. Rate Limiting
Rate limiting refers to allocating a specific amount of bandwidth or
packets per second to specific traffic types. This technique is
widely used to mitigate well-known protocol attacks such as the TCP-
SYN attack where a large number of resources get allocated for
spoofed TCP traffic. Although this technique does not stop an
attack, it can sometimes lessen the damage and impact on a specific
service. However, it can also make the impact of a DDoS attack much
worse if the rate limiting is impacting (i.e. discarding) more
legitimate traffic.
2.8.5. Specific Control Plane Traffic Enhancements
Some ISPs are starting to use capabilities which are available from
some vendors to simplify the filtering and rate-limiting of control
traffic. Control traffic here refers to the routing control plane
and management plane traffic that requires CPU cycles. A DoS attack
against any control plane traffic can therefore be much more damaging
to a critical device than other types of traffic. No consistent
deployment of this capability was found at the time of this writing.
Kaeo Expires March 2, 2007 [Page 33]
Internet-Draft OPSEC Practices August 2006
3. Security Considerations
This entire document deals with current security practices in large
ISP environments. It lists specific practices used in today's
environments and as such does not in itself pose any security risk.
Kaeo Expires March 2, 2007 [Page 34]
Internet-Draft OPSEC Practices August 2006
4. IANA Considerations
This document has no actions for IANA.
Kaeo Expires March 2, 2007 [Page 35]
Internet-Draft OPSEC Practices August 2006
5. Acknowledgments
The editor gratefully acknowledges the contributions of: George
Jones, who has been instrumental in providing guidance and direction
for this document and the insighful comments from Ross Callon, Ron
Bonica, Ryan Mcdowell, Gaurab Upadhaya, Warren Kumari, Pekka Savola,
Fernando Gont, Chris Morrow, Ted Seely, Donald Smith and the numerous
ISP operators who supplied the information which is depicted in this
document.
Kaeo Expires March 2, 2007 [Page 36]
Internet-Draft OPSEC Practices August 2006
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, May 2000.
[RFC2828] Shirey, R., "Internet Security Glossary", RFC 2828,
May 2000.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
July 2003.
[RFC3682] Gill, V., Heasley, J., and D. Meyer, "The Generalized TTL
Security Mechanism (GTSM)", RFC 3682, February 2004.
[RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed
Networks", BCP 84, RFC 3704, March 2004.
[RFC3882] Turk, D., "Configuring BGP to Block Denial-of-Service
Attacks", RFC 3882, September 2004.
6.2. Informational References
[I-D.ietf-v6ops-icmpv6-filtering-recs]
Davies, E. and J. Mohacsi, "Recommendations for Filtering
ICMPv6 Messages in Firewalls",
draft-ietf-v6ops-icmpv6-filtering-recs-02 (work in
progress), July 2006.
[I-D.lewis-infrastructure-security]
Lewis, D., "Service Provider Infrastructure Security",
draft-lewis-infrastructure-security-00 (work in progress),
June 2006.
[I-D.savola-bcp84-urpf-experiences]
Savola, P., "Experiences from Using Unicast RPF",
draft-savola-bcp84-urpf-experiences-01 (work in progress),
June 2006.
[I-D.savola-rtgwg-backbone-attacks]
Savola, P., "Backbone Infrastructure Attacks and
Protections", draft-savola-rtgwg-backbone-attacks-02 (work
Kaeo Expires March 2, 2007 [Page 37]
Internet-Draft OPSEC Practices August 2006
in progress), July 2006.
Kaeo Expires March 2, 2007 [Page 38]
Internet-Draft OPSEC Practices August 2006
Appendix A. Protocol Specific Attacks
This section will list many of the traditional protocol based attacks
which have been observed over the years to cause malformed packets
and/or exploit protocol deficiencies. Note that they all exploit
vulnerabilities in the actual protocol itself and often, additional
authentication and auditing mechanisms are now used to detect and
mitigate the impact of these attacks. The list is not exhaustive but
is a fraction of the representation of what types of attacks are
possible for varying protocols.
A.1. Layer 2 Attacks
o ARP Flooding
A.2. IPv4 Protocol Based Attacks
o IP Addresses, either source or destination, can be spoofed which
in turn can circumvent established filtering rules.
o IP Source Route Option can allows attackers to establish stealth
TCP connections
o IP Record Route Option can discloses information about the
topology of the network.
o IP header that is too long or too short can cause DoS attacks to
devices.
o IP Timestamp Option can leak information which can be used to
discern network behavior.
o Fragmentation attacks which can vary widely - more detailed
information can be found at http://www-src.lip6.fr/homepages/
Fabrice.Legond-Aubry/www.ouah.org/fragma.html
o IP ToS field (or the Differentiated Services (DSCP) field) can be
used to reroute or reclassify traffic based on specified
precedence.
o IP checksum field has been used for scanning purposes, for example
when some firewalls did not check the checksum and allowed an
attacker to differentiate when the response came from an end-
system, and when from a firewall
Kaeo Expires March 2, 2007 [Page 39]
Internet-Draft OPSEC Practices August 2006
o IP TTL field can be used to bypass certain network based intrusion
detection systems and to map network behavior.
A.2.1. Higher Layer Protocol Attacks
The following lists additional attacks but does not explicitly
numerate them in detail. It is for informational purposes only.
o IGMP oversized packet
o ICMP Source Quench
o ICMP Mask Request
o ICMP Large Packet (> 1472)
o ICMP Oversized packet (>65536)
o ICMP Flood
o ICMP Broadcast w/ Spoofed Source (Smurf Attack)
o ICMP Error Packet Flood
o ICMP Spoofed Unreachable
o TCP Packet without Flag
o TCP Oversized Packet
o TCP FIN bit with no ACK bit
o TCP Packet with URG/OOB flag (Nuke Attack)
o SYN Fragments
o SYN Flood
o SYN with IP Spoofing (Land Attack)
o SYN and FIN bits set
o TCP port scan attack
o UDP spoofed broadcast echo (Fraggle Attack)
Kaeo Expires March 2, 2007 [Page 40]
Internet-Draft OPSEC Practices August 2006
o UDP attack on diagnostic ports (Pepsi Attack)
A.3. IPv6 Attacks
Any of the above-mentioned IPv4 attacks could be used in IPv6
networks with the exception of any fragmentation and broadcast
traffic, which operate differently in IPv6. Note that all of these
attacks are based on either spoofing or misusing any part of the
protocol field(s).
Today, IPv6 enabled hosts are starting to be used to create IPv6
tunnels which can effectively hide botnet and other malicious traffic
if firewalls and network flow collection tools are not capable of
detecting this traffic. The security measures used for protecting
IPv6 infrastructures should be the same as in IPv4 networks but with
additional considerations for IPv6 network operations which may be
different from IPv4.
Kaeo Expires March 2, 2007 [Page 41]
Internet-Draft OPSEC Practices August 2006
Author's Address
Merike Kaeo
Double Shot Security, Inc.
3518 Fremont Avenue North #363
Seattle, WA 98103
U.S.A.
Phone: +1 310 866 0165
Email: merike@doubleshotsecurity.com
Kaeo Expires March 2, 2007 [Page 42]
Internet-Draft OPSEC Practices August 2006
Full Copyright Statement
Copyright (C) The Internet Society (2006).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Intellectual Property
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Acknowledgment
Funding for the RFC Editor function is provided by the IETF
Administrative Support Activity (IASA).
Kaeo Expires March 2, 2007 [Page 43]
