draft-ietf-netconf-reverse-ssh-02.txt   draft-ietf-netconf-reverse-ssh-03.txt 
NETCONF Working Group K. Watsen NETCONF Working Group K. Watsen
Internet-Draft Juniper Networks Internet-Draft Juniper Networks
Updates: 4253 (if approved) November 2013 Updates: 4253 (if approved) February 14, 2014
Intended status: Standards Track Intended status: Standards Track
Expires: May 05, 2014 Expires: August 18, 2014
Reverse Secure Shell (Reverse SSH) Reverse Secure Shell (Reverse SSH)
draft-ietf-netconf-reverse-ssh-02 draft-ietf-netconf-reverse-ssh-03
Abstract Abstract
This memo presents a technique for a NETCONF server to initiate a SSH This memo presents a technique for a NETCONF server to initiate a SSH
connection to a NETCONF client. This is accomplished by the NETCONF connection to a NETCONF client. This is accomplished by the NETCONF
client listening on IANA-assigned TCP port YYYY and starting the SSH client listening on IANA-assigned TCP port YYYY and starting the SSH
client protocol immediately after accepting a TCP connection on it. client protocol immediately after accepting a TCP connection on it.
This role-reversal is necessary as the NETCONF server must also be This role-reversal is necessary as the NETCONF server must also be
the SSH Server, in order for the NETCONF client to open the IANA- the SSH Server, in order for the NETCONF client to open the IANA-
assigned SSH subsystem "netconf". assigned SSH subsystem "netconf".
skipping to change at page 1, line 37 skipping to change at page 1, line 37
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 05, 2014. This Internet-Draft will expire on August 18, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
skipping to change at page 2, line 18 skipping to change at page 2, line 18
Table of Contents Table of Contents
1. Requirements Terminology . . . . . . . . . . . . . . . . . . 2 1. Requirements Terminology . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2.1. Applicability Statement . . . . . . . . . . . . . . . . . 2 2.1. Applicability Statement . . . . . . . . . . . . . . . . . 2
2.2. Update to RFC 4253 . . . . . . . . . . . . . . . . . . . 3 2.2. Update to RFC 4253 . . . . . . . . . . . . . . . . . . . 3
3. Benefits to Device Management . . . . . . . . . . . . . . . . 3 3. Benefits to Device Management . . . . . . . . . . . . . . . . 3
4. The Reverse SSH Protocol . . . . . . . . . . . . . . . . . . 4 4. The Reverse SSH Protocol . . . . . . . . . . . . . . . . . . 4
5. SSH Server Identification and Verification . . . . . . . . . 5 5. SSH Server Identification and Verification . . . . . . . . . 5
6. Device Configuration . . . . . . . . . . . . . . . . . . . . 6 6. Device Configuration . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12 7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
10. Normative References . . . . . . . . . . . . . . . . . . . . 14 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 15 10.1. Normative References . . . . . . . . . . . . . . . . . . 8
A.1. 01 to 02 . . . . . . . . . . . . . . . . . . . . . . . . 15 10.2. Informative References . . . . . . . . . . . . . . . . . 9
A.2. 00 to 01 . . . . . . . . . . . . . . . . . . . . . . . . 15 Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 9
A.1. 02 to 03 . . . . . . . . . . . . . . . . . . . . . . . . 9
A.2. 01 to 02 . . . . . . . . . . . . . . . . . . . . . . . . 9
A.3. 00 to 01 . . . . . . . . . . . . . . . . . . . . . . . . 10
1. Requirements Terminology 1. Requirements Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
2. Introduction 2. Introduction
This memo presents a technique for a NETCONF [RFC6241] server to This memo presents a technique for a NETCONF [RFC6241] server to
skipping to change at page 3, line 20 skipping to change at page 3, line 25
verification of the other party. In such circumstances, allowing the verification of the other party. In such circumstances, allowing the
SSH server to contact the SSH client would open new vulnerabilities. SSH server to contact the SSH client would open new vulnerabilities.
Therefore, any use of Reverse SSH for purposes other than NETCONF Therefore, any use of Reverse SSH for purposes other than NETCONF
will need a thorough, contextual security analysis. will need a thorough, contextual security analysis.
2.2. Update to RFC 4253 2.2. Update to RFC 4253
This document updates the SSH Transport Layer Protocol [RFC4253] only This document updates the SSH Transport Layer Protocol [RFC4253] only
by removing the restriction in Section 4 (Connection Setup) of by removing the restriction in Section 4 (Connection Setup) of
[RFC4252] that the SSH Client must initiate the transport connection. [RFC4252] that the SSH Client must initiate the transport connection.
Security implications related to this change are discussed in the Security implications related to this change are discussed in
Security Considerations (Section 7) section. Security Considerations (Section 7).
3. Benefits to Device Management 3. Benefits to Device Management
The SSH protocol is nearly ubiquitous for device management, as it is The SSH protocol is nearly ubiquitous for device management, as it is
the transport for the command-line applications `ssh`, `scp`, and the transport for the command-line applications `ssh`, `scp`, and
`sftp` and is the required transport for the NETCONF protocol `sftp` and is the required transport for the NETCONF protocol
[RFC6241]. However, all these SSH-based protocols expect the network [RFC6241]. However, all these SSH-based protocols expect the network
element to be the SSH server. element to be the SSH server.
Reverse SSH enables the network element to consistently be the SSH Reverse SSH enables the network element to consistently be the SSH
server regardless of which peer initiates the underlying TCP server regardless of which peer initiates the underlying TCP
connection. Maintaining the role of SSH Server is both necessary and connection. Maintaining the role of SSH Server is both necessary and
desirable. It is necessary because SSH channels and subsystems can desirable. It is necessary because SSH channels and subsystems can
only be opened on the SSH Server. It is desirable because it only be opened on the SSH Server. It is desirable because it
conviently leverages infrastructure that may be deployed for host-key conveniently leverages infrastructure that may be deployed for host-
verification and user authentication. key verification and user authentication.
Reverse SSH is useful for both initial deployment and on-going device Reverse SSH is useful for both initial deployment and on-going device
management and may be used to enable any of the following scenarios: management and may be used to enable any of the following scenarios:
o The network element may proactively "call home" after being o The network element may proactively "call home" after being
powered on for the first time to register itself with its powered on for the first time to register itself with its
management system. management system.
o The network element may access the network in a way that o The network element may access the network in a way that
dynamically assigns it an IP address and it doesn't register its dynamically assigns it an IP address and it doesn't register its
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management connections believing it is easier to secure one open- management connections believing it is easier to secure one open-
port in the data center than to have an open port on each network port in the data center than to have an open port on each network
element in the network. element in the network.
One key benefit of using SSH as the transport protocol is its ability One key benefit of using SSH as the transport protocol is its ability
to multiplex an unspecified number of independently flow-controlled to multiplex an unspecified number of independently flow-controlled
TCP sessions [RFC4254]. This is valuable as the network element only TCP sessions [RFC4254]. This is valuable as the network element only
needs to be configured to initiate a single Reverse SSH connection to needs to be configured to initiate a single Reverse SSH connection to
the management system, regardless the number of TCP-based protocols the management system, regardless the number of TCP-based protocols
the management system wishes to support. For instance, in addition the management system wishes to support. For instance, in addition
to having a SSH channel for NETCONF, management system may "pin up" to having a SSH channel for NETCONF, the management system may "pin
channels for Syslog, SNMP, or file-transfers. up" channels for Syslog, SNMP, or file-transfers.
4. The Reverse SSH Protocol 4. The Reverse SSH Protocol
The NETCONF server's perspective (e.g. the network element) The NETCONF server's perspective (e.g., the network element)
o The NETCONF server initiates a TCP connection to the NETCONF o The NETCONF server initiates a TCP connection to the NETCONF
client on the IANA-assigned Reverse SSH port YYYY. client on the IANA-assigned Reverse SSH port YYYY.
o The TCP connection is accecpted and a TCP session is established. o The TCP connection is accepted and a TCP session is established.
o Using this TCP connection, the NETCONF server immediately starts o Using this TCP connection, the NETCONF server immediately starts
the SSH Server protocol. That is, the next message sent on the the SSH Server protocol. That is, the next message sent on the
TCP stream is SSH's Protocol Version Exchange message (section TCP stream is SSH's Protocol Version Exchange message (section
4.2, [RFC4253]). 4.2, [RFC4253]).
The NETCONF client's perspective (e.g. the management system) o The SSH connection is established.
The NETCONF client's perspective (e.g., the management system)
o The NETCONF client listens for TCP connections on the IANA- o The NETCONF client listens for TCP connections on the IANA-
assigned SSH port YYYY. assigned SSH port YYYY.
o The NETCONF client accepts an incoming TCP connection and a TCP o The NETCONF client accepts an incoming TCP connection and a TCP
session is established. session is established.
o Using this TCP connection, the NETCONF client immediately starts o Using this TCP connection, the NETCONF client immediately starts
the SSH Client protocol, starting with sending the SSH's Protocol the SSH Client protocol, starting with sending the SSH's Protocol
Version Exchange message (section 4.2, [RFC4253]). Version Exchange message (section 4.2, [RFC4253]).
o The SSH connection is established.
5. SSH Server Identification and Verification 5. SSH Server Identification and Verification
When the management system accepts a new incoming connection, it When the management system accepts a new incoming connection, it
needs to authenticate the remote peer. Ultimately, this comes down needs to authenticate the remote peer. Ultimately, this entails
to identifying the peer and verifying its SSH host key. identifying the peer and verifying its SSH host key.
Due to Reverse SSH having the network element initiate the TCP Due to Reverse SSH having the network element initiate the TCP
connection, the first data the management system has to identify it connection, the first data the management system has to identify it
with is the source IP address of the TCP connection. But this with is the source IP address of the TCP connection. But this
approach only works in networks that only use static addresses. approach is limited as it only works in networks that use known
static addresses.
To support network-elements having dynamically-assigned IP addresses To support network-elements having dynamically-assigned IP addresses
or deployed behind gateways that translate their IP address (e.g. or deployed behind gateways that translate their IP address (e.g.,
NAT), the management system MAY identify the device using its SSH NAT), the management system MAY identify the device using its SSH
host key. For instance, a fingerprint of the network element's host host key. For instance, a fingerprint of the network element's host
key could be used as an identifier since the probability of collision key could be used as an identifier since the probability of collision
is acceptibly low. But this solution requires the management system is acceptably low. But this solution requires the management system
to be configured with each device's host key each time it changes. to be configured with each device's host key each time it changes.
Yet another option for identifying the network element if for it's Yet another option for identifying the network element is for its
host key to encode its identity, such as if it were a certificate. host key to encode its identity, such as if it were a certificate.
This option enables the host key to change over time, but brings the This option enables the host key to change over time, but brings the
next issue of how the mangement element can verify the network next issue of how the mangement element can verify the network
element's host key is authentice. element's host key is authentic.
The security of SSH is anchored in the ability for the SSH client to The security of SSH is anchored in the ability for the SSH client to
verify the SSH server's hostkey. Typically this is done by comparing verify the SSH server's hostkey. Typically this is done by comparing
the host key presented by the SSH server with one that was previously the host key presented by the SSH server with one that was previously
configured on the SSH client, looking it up in a local database using configured on the SSH client, looking it up in a local database using
the identity of the SSH client as the lookup key. Nothing changes the identity of the SSH client as the lookup key. Nothing changes
regarding this requirement due to the direction reversal of the regarding this requirement due to the direction reversal of the
underlying TCP connection. To ensure security, the management system underlying TCP connection. To ensure security, the management system
MUST verify the network element's SSH host key each time a SSH MUST verify the network element's SSH host key each time a SSH
session is established. session is established.
However, configuring distinct host keys on the management system However, configuring distinct host keys on the management system
doesn't scale well, which is an important consideration to a network doesn't scale well, which is an important consideration to a network
management system. A more scalable strategy is to have the network management system. A more scalable strategy is to have the network
element's host key signed by a common trusted key, such as a element's host key signed by a common trusted key, such as a
certificate authority. Thus, the mangement system only needs to certificate authority. Thus, the mangement system only needs to
trust a single public key, which vouches for the authenticity of the trust a single public key, which vouches for the authenticity of the
network element's specific public key. various network element public keys.
Since both the identification and verification issues are addressed Since both the identification and verification issues are addressed
using certificates, this draft RECOMMENDS network elements use a host using certificates, this draft RECOMMENDS network elements use a host
key that can encode a unique (e.g. its serial number) and be signed key that can encode a unique (e.g., its serial number) and be signed
by a common trust anchor (e.g. a certificate authority). Examples of by a common trust anchor (e.g., a certificate authority). Examples
suitable public host keys are the X.509v3 keys defined in defined in of suitable public host keys are the X.509v3 keys defined in defined
[RFC6187]. in [RFC6187].
6. Device Configuration 6. Device Configuration
This section defines a YANG [RFC6020] module to configure Reverse SSH Configuring a device to initiate a Reverse SSH connection entails it
on the device. This YANG module enables a NETCONF client to knowing what IP address it should connect to and what SSH host-key it
generically manage a NETCONF server's Reverse SSH configuration. Key should present. A complete YANG module [RFC6020] to configure
aspects of this YANG module include support for more than one Reverse SSH is defined in [I.D.kwatsen-netconf-server] . This YANG
application, more than one server per application, and a reconnection module enables a NETCONF client to generically manage a NETCONF
strategy. server's Reverse SSH configuration. Key aspects of this YANG module
include support for more than one application, more than one server
Configuration Example per application, and a reconnection strategy.
<config xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
<reverse-ssh xmlns="urn:ietf:params:xml:ns:yang:ietf-reverse-ssh">
<applications>
<application>
<name>config-mgr</name>
<description>
This entry requests the device to periodically
connect to the Configuration Manager application
</description>
<servers>
<server>
<host>config-mgr1.acme.com</host>
<port>7022</port>
</server>
<server>
<host>config-mgr2.acme.com</host>
<port>7022</port>
</server>
</servers>
<host-keys>
<host-key>
<name>ssh_host_key_cert</name>
</host-key>
<host-key>
<name>ssh_host_key_cert2</name>
</host-key>
</host-keys>
<connection-type>
<periodic>
<timeout-mins>8</timeout-mins>
<linger-secs>10</linger-secs>
</periodic>
</connection-type>
<reconnect-strategy>
<start-with>last-connected</start-with>
<interval-secs>10</interval-secs>
<count-max>4</count-max>
</reconnect-strategy>
<keep-alive-strategy>
<interval-secs>5</interval-secs>
<count-max>3</count-max>
</keep-alive-strategy>
</application>
<application>
<name>log-monitor</name>
<description>
This entry requests the device to mantain a
persistent connection to the Log Monitoring
application
</description>
<servers>
<server>
<host>log-mon1.acme.com</host>
<port>7514</port>
</server>
<server>
<host>log-monitor2.acme.com</host>
<port>7514</port>
</server>
</servers>
<host-keys>
<host-key>
<name>ssh_host_key_hmac</name>
</host-key>
</host-keys>
<connection-type>
<persistent/>
</connection-type>
<reconnect-strategy>
<start-with>last-connected</start-with>
<interval-secs>10</interval-secs>
<count-max>4</count-max>
</reconnect-strategy>
<keep-alive-strategy>
<interval-secs>5</interval-secs>
<count-max>3</count-max>
</keep-alive-strategy>
</application>
</applications>
</reverse-ssh>
</config>
The YANG Module
module ietf-reverse-ssh {
namespace "urn:ietf:params:xml:ns:yang:ietf-reverse-ssh";
prefix "rssh";
import ietf-inet-types { prefix inet; }
organization
"IETF NETCONF (Network Configuration Protocol) Working Group";
contact
"WG Web: <http://tools.ietf.org/wg/netconf/>
WG List: <mailto:netconf@ietf.org>
WG Chair: Bert Wijnen
<mailto:bertietf@bwijnen.net>
WG Chair: Mehmet Ersue
<mailto:mehmet.ersue@nsn.com>
Editor: Kent Watsen
<mailto:kwatsen@juniper.net>";
revision 2013-06-18 {
description "Initial conception";
reference "RFC XXXX: Reverse SSH";
}
// RFC Ed.: replace XXXX with actual
// RFC number and remove this note
container reverse-ssh {
container applications {
description
"All the application that the device
initiates Reverse SSH connections to";
list application {
key name;
min-elements 1;
leaf name {
mandatory true;
type string {
length 1..64;
}
description
"The name of the application the device is
connecting to";
}
leaf description {
type string;
description
"An optional description for the application";
}
container servers {
description
"An ordered listing of the application's
servers that the device should attempt
connecting to.";
list server {
key host;
min-elements 1;
ordered-by user;
leaf host {
mandatory true;
type inet:host;
description
"IP address or domain-name for
the server";
}
leaf port {
type inet:port-number;
description
"The IP port for this server.
The device will use the
IANA-assigned port if not
specified.";
}
}
}
container host-keys {
description
"An ordered listing of the SSH host keys the
device should advertise to the application.";
list host-key {
key name;
min-elements 1;
ordered-by user;
leaf name {
mandatory true;
type string {
length 1..64;
}
description
"The name of a host key the device
should advertise during the SSH
key exchange.";
}
}
}
container connection-type {
description "Indicates the application's
preference for how the device's
connection is maintained.";
choice connection-type {
default persistent-connection;
case persistent-connection {
leaf persistent {
type empty;
}
}
case periodic-connection {
container periodic {
leaf timeout-mins {
type uint8;
default 5;
units minutes;
description
"The maximum amount of unconnected
time the device will wait until
establishing a connection to the
applications again to send it.
The device may establish a
connection before this time if
it has data it needs to send to
the device.";
}
leaf linger-secs {
type uint8;
default 30;
units seconds;
description
"The amount of time the device should
wait after last receiving data from
or sending data to the device before
closing its connection to the app.";
}
}
}
}
}
container reconnect-strategy {
leaf start-with {
default first-listed;
type enumeration {
enum first-listed;
enum last-connected;
}
}
leaf interval-secs {
type uint8;
units seconds;
default 5;
description
"time delay between connection attempts";
}
leaf count-max {
type uint8;
default 3;
description
"num times try to connect to a server";
}
}
container keep-alive-strategy {
leaf interval-secs {
type uint8;
units seconds;
default 15;
description
"Sets a timeout interval in seconds after
which if no data has been received from
the client, a message will be sent to
request a response from the SSH client.
A value of '0' indicates that no messages
should be sent.";
}
leaf count-max {
type uint8;
default 3;
description
"Sets the number of keep alive messages
that may be sent without receiving any
response from the SSH client before
assuming the SSH client is no longer
alive. If this threshold is reached
the device will disconnect the SSH
session. The keep alive interval timer
is reset after each transmission. Thus,
an unresponsive SSH client will be
disconnected after approximately
'count-max * interval-secs' seconds.";
}
}
}
}
}
}
7. Security Considerations 7. Security Considerations
This RFC deviates from standard SSH protocol usage by allowing the This RFC deviates from standard SSH protocol usage by allowing the
SSH server to initiate the TCP connection. This conflicts with SSH server to initiate the TCP connection. This conflicts with
section 4 of the SSH Transport Layer Protocol RFC [RFC4253], which section 4 of the SSH Transport Layer Protocol RFC [RFC4253], which
states "The client initiates the connection". However this statement states "The client initiates the connection". However this statement
is made without rationalization and it's not clear how it impacts the is made without rationalization and it's not clear how it impacts the
security of the protocol, so this section analyzes the security security of the protocol, so this section analyzes the security
offered by having the client initiate the connection. offered by having the client initiate the connection.
skipping to change at page 12, line 50 skipping to change at page 7, line 28
That said, this RFC recommends implementations use a public host key That said, this RFC recommends implementations use a public host key
algorithm that certifies the SSH server's identity. The identity can algorithm that certifies the SSH server's identity. The identity can
be any unique identifier, such as a device's serial number or a be any unique identifier, such as a device's serial number or a
deployment-specific value. If this recommendation is followed, then deployment-specific value. If this recommendation is followed, then
no information from the TCP layer would be needed to lookup the no information from the TCP layer would be needed to lookup the
device in a local database and therefore the directionality of the device in a local database and therefore the directionality of the
TCP layer is clearly inconsequential. TCP layer is clearly inconsequential.
The SSH protocol negotiates which algorithms it will use during key The SSH protocol negotiates which algorithms it will use during key
exchange (Section 7.1 (Algortihm Negotition) in [RFC4253]). The exchange (Section 7.1 (Algorithm Negotiation) in [RFC4253]). The
algorithm selected is essentially the first compatible algorithm algorithm selected is essentially the first compatible algorithm
listed by the SSH client that is also listed by the SSH server. For listed by the SSH client that is also listed by the SSH server. For
a network management application, there may be a need to advertise a a network management application, there may be a need to advertise a
large number of algorithms to be compatible with the various devices large number of algorithms to be compatible with the various devices
it manages. The SSH client SHOULD order its list of public host key it manages. The SSH client SHOULD order its list of public host key
algorithms such that all the certifiable public host key algorithms algorithms such that all the certifiable public host key algorithms
are listed first. Additionally, when possible, SSH servers SHOULD are listed first. Additionally, when possible, SSH servers SHOULD
only list certifiable public host key algorithms. Note that since only list certifiable public host key algorithms. Note that since
the SSH server would have to be configured to know which IP address the SSH server would have to be configured to know which IP address
it needs to connect to, it is expected that it will also be it needs to connect to, it is expected that it will also be
skipping to change at page 13, line 28 skipping to change at page 8, line 5
a form of identity. A potential concern with using a serial number a form of identity. A potential concern with using a serial number
is that the SSH protocol passes the SSH server's host-key in the is that the SSH protocol passes the SSH server's host-key in the
clear and many times serial numbers encode revealing information clear and many times serial numbers encode revealing information
about the device, such as what kind of device it is and when it was about the device, such as what kind of device it is and when it was
manufactured. While there is little security in trying to hide this manufactured. While there is little security in trying to hide this
information from an attacker, it is understood that some deployments information from an attacker, it is understood that some deployments
may want to keep this information private. If this is a concern, may want to keep this information private. If this is a concern,
deployments MAY consider using instead a hash of the device's serial deployments MAY consider using instead a hash of the device's serial
number or an application-specified unique identifier. number or an application-specified unique identifier.
An attacker could DoS the application by having it to perform An attacker could DoS the application by having it perform
computationally expensive operations, before deducing that the computationally expensive operations, before deducing that the
attacker doesn't posses a valid key. This is no different than any attacker doesn't posses a valid key. This is no different than any
secured service and all common precautions apply (e.g. blacklisting secured service and all common precautions apply (e.g., blacklisting
the source address after a set number of unsuccessful login the source address after a set number of unsuccessful login
attempts). attempts).
8. IANA Considerations 8. IANA Considerations
This document requests that IANA assigns a TCP port number in the This document requests that IANA assigns a TCP port number in the
"Registered Port Numbers" range with the service name "reverse-ssh". "Registered Port Numbers" range with the service name "reverse-ssh".
This port will be the default port for the Reverse SSH protocol and This port will be the default port for the Reverse SSH protocol and
will be used when the NETCONF server needs to initiate a connection will be used when the NETCONF server needs to initiate a connection
to a NETCONF client using SSH. Below is the registration template to a NETCONF client using SSH. Below is the registration template
skipping to change at page 14, line 13 skipping to change at page 8, line 37
Port Number: YYYY Port Number: YYYY
9. Acknowledgements 9. Acknowledgements
The author would like to thank for following for lively discussions The author would like to thank for following for lively discussions
on list and in the halls (ordered by last name): Andy Bierman, Martin on list and in the halls (ordered by last name): Andy Bierman, Martin
Bjorklund, Mehmet Ersue, Wes Hardaker, Stephen Hanna, David Bjorklund, Mehmet Ersue, Wes Hardaker, Stephen Hanna, David
Harrington, Jeffrey Hutzelman, Mouse, Russ Mundy, Tom Petch, Peter Harrington, Jeffrey Hutzelman, Mouse, Russ Mundy, Tom Petch, Peter
Saint-Andre, Joe Touch, Sean Turner, Bert Wijnen. Saint-Andre, Joe Touch, Sean Turner, Bert Wijnen.
10. Normative References 10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels ", BCP 14, RFC 2119, March 1997. Requirement Levels ", BCP 14, RFC 2119, March 1997.
[RFC4250] Lehtinen, S. and C. Lonvick, Ed., "The Secure Shell (SSH) [RFC4250] Lehtinen, S. and C. Lonvick, "The Secure Shell (SSH)
Protocol Assigned Numbers ", RFC 4250, December 2005. Protocol Assigned Numbers ", RFC 4250, December 2005.
[RFC4251] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) [RFC4251] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
Protocol Architecture ", RFC 4251, January 2006. Protocol Architecture ", RFC 4251, January 2006.
[RFC4252] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) [RFC4252] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
Authentication Protocol ", RFC 4252, January 2006. Authentication Protocol ", RFC 4252, January 2006.
[RFC4253] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) [RFC4253] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
Transport Layer Protocol ", RFC 4253, January 2006. Transport Layer Protocol ", RFC 4253, January 2006.
[RFC4254] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) [RFC4254] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
Connection Protocol ", RFC 4254, January 2006. Connection Protocol ", RFC 4254, January 2006.
[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for [RFC6020] Bjorklund, M., "YANG - A Data Modeling Language for the
the Network Configuration Protocol (NETCONF) ", RFC 6020, Network Configuration Protocol (NETCONF) ", RFC 6020,
October 2010. October 2010.
[RFC6187] Igoe, K. and D. Stebila, "X.509v3 Certificates for Secure [RFC6187] Igoe, K. and D. Stebila, "X.509v3 Certificates for Secure
Shell Authentication ", RFC 6187, March 2011. Shell Authentication ", RFC 6187, March 2011.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., [RFC6241] Enns, R., Bjorklund, M., Schoenwaelder, J., and A.
and A. Bierman, Ed., "NETCONF Configuration Protocol", RFC Bierman, "NETCONF Configuration Protocol", RFC 6241, June
6241, June 2011. 2011.
[RFC6242] Wasserman, M., Ed., "Using the NETCONF Protocol over [RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure
Secure Shell (SSH)", RFC 6242, June 2011. Shell (SSH)", RFC 6242, June 2011.
[RFC6335] Cotton, M., Ed., Eggert, L., Ed., Touch, J., Ed., [RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
Westerlund, M., Ed., and S. Cheshire, Ed., "Internet Cheshire, "Internet Assigned Numbers Authority (IANA)
Assigned Numbers Authority (IANA) Procedures for the Procedures for the Management of the Service Name and
Management of the Service Name and Transport Protocol Port Transport Protocol Port Number Registry", RFC 6335, August
Number Registry", RFC 6335, August 2011. 2011.
10.2. Informative References
[I.D.kwatsen-netconf-server]
Watsen, K. and J. Schoenwaelder, "A YANG Data Model for
NETCONF Server Configuration", RFC 6242, June 2011.
Appendix A. Change Log Appendix A. Change Log
A.1. 01 to 02 A.1. 02 to 03
Updated Device Configuration section to reference
[I.D.kwatsen-netconf-server]
A.2. 01 to 02
Added Applicability Statement Added Applicability Statement
Removed references to ZeroConf / ZeroTouch Removed references to ZeroConf / ZeroTouch
Clarified the protocol section Clarified the protocol section
Added a section for identification and verification Added a section for identification and verification
A.2. 00 to 01 A.3. 00 to 01
removed the hmac-* family of algorithms Removed the hmac-* family of algorithms
Author's Address Author's Address
Kent Watsen Kent Watsen
Juniper Networks Juniper Networks
EMail: kwatsen@juniper.net EMail: kwatsen@juniper.net
 End of changes. 39 change blocks. 
348 lines changed or deleted 85 lines changed or added

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