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Network Working Group Request for Comments: 2667 Category: Standards Track |
D. Thaler Microsoft August 1999 |
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
Copyright © The Internet Society (1999). All Rights Reserved.
This memo defines a Management Information Base (MIB) for use with network management protocols in the Internet community. In particular, it describes managed objects used for managing tunnels of any type over IPv4 networks. Extension MIBs may be designed for managing protocol-specific objects. Likewise, extension MIBs may be designed for managing security-specific objects. This MIB does not support tunnels over non-IPv4 networks (including IPv6 networks). Management of such tunnels may be supported by other MIBs.
1 Abstract
2 Introduction
3 The SNMP Network Management Framework
4 Overview
4.1 Relationship to the Interfaces MIB
4.1.1 Layering Model
4.1.2 ifRcvAddressTable
4.1.3 ifEntry
5 Definitions
6 Security Considerations
7 Acknowledgements
8 Author's Address
9 References
10 Intellectual Property Notice
11 Full Copyright Statement
Over the past several years, there have been a number of "tunneling" protocols specified by the IETF (see [28] for an early discussion of the model and examples). This document describes a Management Information Base (MIB) used for managing tunnels of any type over IPv4 networks, including GRE [16,17], IP-in-IP [18], Minimal Encapsulation [19], L2TP [20], PPTP [21], L2F [25], UDP (e.g., [26]), ATMP [22], and IPv6-in-IPv4 [27] tunnels.
Extension MIBs may be designed for managing protocol-specific objects. Likewise, extension MIBs may be designed for managing security-specific objects (e.g., IPSEC [24]), and traffic conditioner [29] objects. Finally, this MIB does not support tunnels over non- IPv4 networks (including IPv6 networks). Management of such tunnels may be supported by other MIBs.
The SNMP Management Framework presently consists of five major components:
Managed objects are accessed via a virtual information store, termed the Management Information Base or MIB. Objects in the MIB are defined using the mechanisms defined in the SMI.
This memo specifies a MIB module that is compliant to the SMIv2. A MIB conforming to the SMIv1 can be produced through the appropriate translations. The resulting translated MIB must be semantically equivalent, except where objects or events are omitted because no translation is possible (use of Counter64). Some machine readable information in SMIv2 will be converted into textual descriptions in SMIv1 during the translation process. However, this loss of machine readable information is not considered to change the semantics of the MIB.
This MIB module contains two tables:
This section clarifies the relationship of this MIB to the Interfaces MIB [23]. Several areas of correlation are addressed in the following subsections. The implementor is referred to the Interfaces MIB document in order to understand the general intent of these areas.
Each logical interface (physical or virtual) has an ifEntry in the Interfaces MIB [23]. Tunnels are handled by creating a logical interface (ifEntry) for each tunnel. These are then correlated, using the ifStack table of the Interfaces MIB, to those interfaces on which the local IPv4 addresses of the tunnels are configured. The basic model, therefore, looks something like this (for example):
| | | | | |
+--+ +---+ +--+ +---+ | |
|IP-in-IP| | GRE | | |
| tunnel | | tunnel | | |
+--+ +---+ +--+ +---+ | |
| | | | | | <== attachment to underlying
+--+ +---------+ +----------+ +--+ interfaces, to be provided
| Physical interface | by ifStack table
+--------------------------------+
The ifRcvAddressTable usage is defined in the MIBs defining the encapsulation below the network layer. For example, if IP-in-IP encapsulation is being used, the ifRcvAddressTable is defined by IP- in-IP.
IfEntries are defined in the MIBs defining the encapsulation below the network layer. For example, if IP-in-IP encapsulation [20] is being used, the ifEntry is defined by IP-in-IP.
The ifType of a tunnel should be set to "tunnel" (131). An entry in the IP Tunnel MIB will exist for every ifEntry with this ifType. An implementation of the IP Tunnel MIB may allow ifEntries to be created via the tunnelConfigTable. Creating a tunnel will also add an entry in the ifTable and in the tunnelIfTable, and deleting a tunnel will likewise delete the entry in the ifTable and the tunnelIfTable.
The use of two different tables in this MIB was an important design decision. Traditionally, ifIndex values are chosen by agents, and are permitted to change across restarts. Allowing row creation directly in the Tunnel Interface Table, indexed by ifIndex, would complicate row creation and/or cause interoperability problems (if each agent had special restrictions on ifIndex). Instead, a separate table is used which is indexed only by objects over which the manager has control. Namely, these are the addresses of the tunnel endpoints and the encapsulation protocol. Finally, an additional manager- chosen ID is used in the index to support protocols such as L2F which allow multiple tunnels between the same endpoints.
TUNNEL-MIB DEFINITIONS ::= BEGIN
Integer32, IpAddress FROM SNMPv2-SMI
RowStatus FROM SNMPv2-TC
MODULE-COMPLIANCE, OBJECT-GROUP FROM SNMPv2-CONF
ifIndex, InterfaceIndexOrZero FROM IF-MIB;
REVISION "9908241200Z" -- August 24, 1999
DESCRIPTION
"Initial version, published as RFC 2667."
::= { transmission 131 }
tunnelMIBObjects OBJECT IDENTIFIER ::= { tunnelMIB 1 }
tunnel OBJECT IDENTIFIER ::= { tunnelMIBObjects 1 }
-- the IP Tunnel MIB-Group
--
-- a collection of objects providing information about
-- IP Tunnels
SYNTAX SEQUENCE OF TunnelIfEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The (conceptual) table containing information on configured
tunnels."
::= { tunnel 1 }
SYNTAX TunnelIfEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry (conceptual row) containing the information on a
particular configured tunnel."
INDEX { ifIndex }
::= { tunnelIfTable 1 }
TunnelIfEntry ::= SEQUENCE {
tunnelIfLocalAddress IpAddress,
tunnelIfRemoteAddress IpAddress,
tunnelIfEncapsMethod INTEGER,
tunnelIfHopLimit Integer32,
tunnelIfSecurity INTEGER,
tunnelIfTOS Integer32
}
SYNTAX IpAddress
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The address of the local endpoint of the tunnel (i.e., the
source address used in the outer IP header), or 0.0.0.0 if
unknown."
::= { tunnelIfEntry 1 }
SYNTAX IpAddress
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The address of the remote endpoint of the tunnel (i.e., the
destination address used in the outer IP header), or 0.0.0.0
if unknown."
::= { tunnelIfEntry 2 }
SYNTAX INTEGER {
other(1), -- none of the following
direct(2), -- no intermediate header
gre(3), -- GRE encapsulation
minimal(4), -- Minimal encapsulation
l2tp(5), -- L2TP encapsulation
pptp(6), -- PPTP encapsulation
l2f(7), -- L2F encapsulation
udp(8), -- UDP encapsulation
atmp(9) -- ATMP encapsulation
}
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The encapsulation method used by the tunnel. The value
direct indicates that the packet is encapsulated directly
within a normal IPv4 header, with no intermediate header,
and unicast to the remote tunnel endpoint (e.g., an RFC 2003
IP-in-IP tunnel, or an RFC 1933 IPv6-in-IPv4 tunnel). The
value minimal indicates that a Minimal Forwarding Header
(RFC 2004) is inserted between the outer header and the
payload packet. The value UDP indicates that the payload
packet is encapsulated within a normal UDP packet (e.g., RFC
1234). The remaining protocol-specific values indicate that
a header of the protocol of that name is inserted between
the outer header and the payload header."
::= { tunnelIfEntry 3 }
SYNTAX Integer32 (0..255)
MAX-ACCESS read-write
STATUS current
DESCRIPTION
"The TTL to use in the outer IP header. A value of 0
indicates that the value is copied from the payload's
header."
::= { tunnelIfEntry 4 }
SYNTAX INTEGER {
none(1), -- no security
ipsec(2), -- IPSEC security
other(3)
}
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The method used by the tunnel to secure the outer IP
header. The value ipsec indicates that IPsec is used
between the tunnel endpoints for authentication or
encryption or both. More specific security-related
information may be available in a MIB for the security
protocol in use."
::= { tunnelIfEntry 5 }
SYNTAX Integer32 (-2..63)
MAX-ACCESS read-write
STATUS current
DESCRIPTION
"The method used to set the high 6 bits of the TOS in the
outer IP header. A value of -1 indicates that the bits are
copied from the payload's header. A value of -2 indicates
that a traffic conditioner is invoked and more information
may be available in a traffic conditioner MIB. A value
between 0 and 63 inclusive indicates that the bit field is
set to the indicated value."
::= { tunnelIfEntry 6 }
SYNTAX SEQUENCE OF TunnelConfigEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The (conceptual) table containing information on configured
tunnels. This table can be used to map a set of tunnel
endpoints to the associated ifIndex value. It can also be
used for row creation. Note that every row in the
tunnelIfTable with a fixed destination address should have a
corresponding row in the tunnelConfigTable, regardless of
whether it was created via SNMP."
::= { tunnel 2 }
SYNTAX TunnelConfigEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An entry (conceptual row) containing the information on a
particular configured tunnel."
INDEX { tunnelConfigLocalAddress,
tunnelConfigRemoteAddress,
tunnelConfigEncapsMethod,
tunnelConfigID }
::= { tunnelConfigTable 1 }
TunnelConfigEntry ::= SEQUENCE {
tunnelConfigLocalAddress IpAddress,
tunnelConfigRemoteAddress IpAddress,
tunnelConfigEncapsMethod INTEGER,
tunnelConfigID Integer32,
tunnelConfigIfIndex InterfaceIndexOrZero,
tunnelConfigStatus RowStatus
}
SYNTAX IpAddress
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The address of the local endpoint of the tunnel, or 0.0.0.0
if the device is free to choose any of its addresses at
tunnel establishment time."
::= { tunnelConfigEntry 1 }
SYNTAX IpAddress
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The address of the remote endpoint of the tunnel."
::= { tunnelConfigEntry 2 }
SYNTAX INTEGER {
other(1), -- none of the following
direct(2), -- no intermediate header
gre(3), -- GRE encapsulation
minimal(4), -- Minimal encapsulation
l2tp(5), -- L2TP encapsulation
pptp(6), -- PPTP encapsulation
l2f(7), -- L2F encapsulation
udp(8), -- UDP encapsulation
atmp(9)
}
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The encapsulation method used by the tunnel."
::= { tunnelConfigEntry 3 }
SYNTAX Integer32 (1..2147483647)
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"An identifier used to distinguish between multiple tunnels
of the same encapsulation method, with the same endpoints.
If the encapsulation protocol only allows one tunnel per set
of endpoint addresses (such as for GRE or IP-in-IP), the
value of this object is 1. For encapsulation methods (such
as L2F) which allow multiple parallel tunnels, the manager
is responsible for choosing any ID which does not conflict
with an existing row, such as choosing a random number."
::= { tunnelConfigEntry 4 }
SYNTAX InterfaceIndexOrZero
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"If the value of tunnelConfigStatus for this row is active,
then this object contains the value of ifIndex corresponding
to the tunnel interface. A value of 0 is not legal in the
active state, and means that the interface index has not yet
been assigned."
::= { tunnelConfigEntry 5 }
SYNTAX RowStatus
MAX-ACCESS read-create
STATUS current
DESCRIPTION
"The status of this row, by which new entries may be
created, or old entries deleted from this table. The agent
need not support setting this object to createAndWait or
notInService since there are no other writable objects in
this table, and writable objects in rows of corresponding
tables such as the tunnelIfTable may be modified while this
row is active.
To create a row in this table for an encapsulation method which does not support multiple parallel tunnels with the same endpoints, the management station should simply use a tunnelConfigID of 1, and set tunnelConfigStatus to createAndGo. For encapsulation methods such as L2F which allow multiple parallel tunnels, the management station may select a pseudo-random number to use as the tunnelConfigID and set tunnelConfigStatus to createAndGo. In the event that this ID is already in use and an inconsistentValue is returned in response to the set operation, the management station should simply select a new pseudo-random number and retry the operation.
Creating a row in this table will cause an interface index to be assigned by the agent in an implementation-dependent manner, and corresponding rows will be instantiated in the ifTable and the tunnelIfTable. The status of this row will become active as soon as the agent assigns the interface index, regardless of whether the interface is operationally up.
Deleting a row in this table will likewise delete the corresponding row in the ifTable and in the tunnelIfTable."
::= { tunnelConfigEntry 6 }
-- conformance information
OBJECT IDENTIFIER ::= { tunnelMIB 2 }
OBJECT IDENTIFIER ::= { tunnelMIBConformance 1 }
tunnelMIBGroups OBJECT IDENTIFIER ::= { tunnelMIBConformance 2 }
-- compliance statements
OBJECT tunnelIfHopLimit
MIN-ACCESS read-only
DESCRIPTION
"Write access is not required."
OBJECT tunnelIfTOS
MIN-ACCESS read-only
DESCRIPTION
"Write access is not required."
OBJECT tunnelConfigStatus
MIN-ACCESS read-only
DESCRIPTION
"Write access is not required."
::= { tunnelMIBCompliances 1 }
-- units of conformance
::= { tunnelMIBGroups 1 }
This MIB contains readable objects whose values provide information related to IP tunnel interfaces. There are also a number of objects that have a MAX-ACCESS clause of read-write and/or read-create, such as those which allow an administrator to dynamically configure tunnels.
While unauthorized access to the readable objects is relatively innocuous, unauthorized access to the write-able objects could cause a denial of service, or could cause unauthorized creation and/or manipulation of tunnels. Hence, the support for SET operations in a non-secure environment without proper protection can have a negative effect on network operations.
SNMPv1 by itself is such an insecure environment. Even if the network itself is secure (for example by using IPSec [24]), even then, there is no control as to who on the secure network is allowed to access and SET (change/create/delete) the objects in this MIB.
It is recommended that the implementers consider the security features as provided by the SNMPv3 framework. Specifically, the use of the User-based Security Model RFC 2574 [12] and the View-based Access Control Model RFC 2575 [15] is recommended.
It is then a customer/user responsibility to ensure that the SNMP entity giving access to this MIB, is properly configured to give access to those objects only to those principals (users) that have legitimate rights to access them.
This MIB module was updated based on feedback from the IETF's Interfaces MIB (IF-MIB) and Point-to-Point Protocol Extensions (PPPEXT) Working Groups.
Dave Thaler
Microsoft Corporation
One Microsoft Way
Redmond, WA 98052-6399
Phone: +1 425 703 8835
EMail: dthaler@microsoft.com
[1] Wijnen, B., Harrington, D. and R. Presuhn, "An Architecture for Describing SNMP Management Frameworks", RFC 2571, April 1999.
[2] Rose, M. and K. McCloghrie, "Structure and Identification of Management Information for TCP/IP-based Internets", STD 16, RFC 1155, May 1990.
[3] Rose, M. and K. McCloghrie, "Concise MIB Definitions", STD 16, RFC 1212, March 1991.
[4] Rose, M., "A Convention for Defining Traps for use with the SNMP", RFC 1215, March 1991.
[5] McCloghrie, K., Perkins, D. and J. Schoenwaelder, "Structure of Management Information Version 2 (SMIv2)", STD 58, RFC 2578, April 1999.
[6] McCloghrie, K., Perkins, D. and J. Schoenwaelder, "Textual Conventions for SMIv2", STD 58, RFC 2579, April 1999.
[7] McCloghrie, K., Perkins, D. and J. Schoenwaelder, "Conformance Statements for SMIv2", STD 58, RFC 2580, April 1999.
[8] Case, J., Fedor, M., Schoffstall, M. and J. Davin, "Simple Network Management Protocol", STD 15, RFC 1157, May 1990.
[9] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Introduction to Community-based SNMPv2", RFC 1901, January 1996.
[10] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Transport Mappings for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1906, January 1996.
[11] Case, J., Harrington D., Presuhn R. and B. Wijnen, "Message Processing and Dispatching for the Simple Network Management Protocol (SNMP)", RFC 2572, April 1999.
[12] Blumenthal, U. and B. Wijnen, "User-based Security Model (USM) for version 3 of the Simple Network Management Protocol (SNMPv3)", RFC 2574, April 1999.
[13] Case, J., McCloghrie, K., Rose, M. and S. Waldbusser, "Protocol Operations for Version 2 of the Simple Network Management Protocol (SNMPv2)", RFC 1905, January 1996.
[14] Levi, D., Meyer, P. and B. Stewart, "SNMPv3 Applications", RFC 2573, April 1999.
[15] Wijnen, B., Presuhn, R. and K. McCloghrie, "View-based Access Control Model (VACM) for the Simple Network Management Protocol (SNMP)", RFC 2575, April 1999.
[16] Hanks, S., Li, T., Farinacci, D. and P. Traina, "Generic Routing Encapsulation (GRE)", RFC 1701, October 1994.
[17] Hanks, S., Li, T., Farinacci, D. and P. Traina, "Generic Routing Encapsulation over IPv4 networks", RFC 1702, October 1994.
[18] Perkins, C., "IP Encapsulation within IP", RFC 2003, October 1996.
[19] Perkins, C., "Minimal Encapsulation within IP", RFC 2004, October 1996.
[20] Townsley, W., Valencia, A., Rubens, A., Pall, G., Zorn, G. and B. Palter, "Layer Two Tunneling Protocol "L2TP"", RFC 2661, August 1999.
[21] Hamzeh, K., Pall, G., Verthein, W. Taarud, J., Little, W. and G. Zorn, "Point-to-Point Tunneling Protocol", RFC 2637, July 1999.
[22] Hamzeh, K., "Ascend Tunnel Management Protocol - ATMP", RFC 2107, February 1997.
[23] McCloghrie, K. and F. Kastenholz. "The Interfaces Group MIB using SMIv2", RFC 2233, November 1997.
[24] R. Atkinson, "Security architecture for the internet protocol", RFC 2401, November 1998.
[25] Valencia, A., Littlewood, M. and T. Kolar. "Cisco Layer Two Forwarding (Protocol) "L2F"", RFC 2341, May 1998.
[26] D. Provan, "Tunneling IPX Traffic through IP Networks", RFC 1234, June 1991.
[27] Gilligan, R. and E. Nordmark. "Transition Mechanisms for IPv6 Hosts and Routers", RFC 1933, April 1996.
[28] Woodburn, R. and D. Mills, "A Scheme for an Internet Encapsulation Protocol: Version 1", RFC 1241, July 1991.
[29] Nichols, K., Blake, S., Baker, F. and D. Black. "Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers", RFC 2474, December 1998.
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