Internetworking Over NBMA James V. Luciani
INTERNET-DRAFT (Bay Networks)
<draft-ietf-ion-nhrp-mobile-nhc-00.txt> Hiroshi Suzuki
(NEC Corporation)
Naganand Doraswamy
(Bay Networks)
David Horton
(CiTR Pty Ltd)
Expires August 1998
NHRP with Mobile NHCs
Status of this Memo
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Abstract
This document describes an extension for Mobile NHCs to use when they
register with their home LIS but initially connect to a non-serving
NHS to do so.
1. Introduction
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
document, are to be interpreted as described in [4].
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This document describes an extension for Mobile NHCs to use when they
wish to register with their home LIS but initially connect to a non-
serving NHS to do so. The reader is encouraged to read [1] for more
details on the NHRP registration process.
2.0 Definition of the NHRP Mobile NHC Authentication Extension
Compulsory = 1
Type = 10 (proposed)
Length = variable
The NHRP Mobile NHC Authentication Extension is carried in NHRP
Registration packets to convey end to end authentication Information.
This extension is used when a mobile NHC initially connects to an NHS
which is not one of its serving NHSs and the mobile NHC and non-
serving NHS are not in a security relationship. The mobile NHC does
this in order to send an NHRP Registration Request, via normal
routing and forwarding processes, to one of its serving NHSs with
which it does have a security relationship. As defined in [1], a
serving NHS is an NHS in the NHC's home LIS with which the NHC will
register. Upon receiving such an NHRP Registration Request, the
serving NHS will do the following: authenticate the sender NHC, set
up a VC to the NHC, and then send an NHRP Resolution Reply in
response on that new VC.
Note that a transit NHS (such as the one to which the mobile NHC
initially connects) MUST ignore an extension which it does not
understand and that an NHS MUST not change the order of extensions in
an NHRP packet. Thus, the end to end semantics of this extension are
preserved without causing changes to existing implementations.
If a serving NHS receives a packet which fails the hop by hop
authentication test defined in [1] then the NHS MUST generate an
Error Indication of type "Authentication Failure" and discard the
packet. However in the case where the NHRP Mobile NHC Authentication
Extension is used as described above, sending an Error Indication is
not possible since no route exists back toward the mobile NHC
assuming a VC does not already exist between the mobile NHC and the
serving NHS which received the NHRP Registration Request. In this
case, the NHRP Registration Request is merely dropped.
2.1 Header Format
The authentication header has the following format:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Security Parameter Index (SPI)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Src Addr... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+ Authentication Data... -+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Security Parameter Index (SPI) can be thought of as an index into a
table that maintains the keys and other information such as a hash
algorithm. Src and Dst communicate either offline using manual keying
or online using a key management protocol to populate this table. The
sending NHRP entity always allocates the SPI and the parameters
associated with it.
The Src Addr field is a variable length field which contains the
address assigned to the outgoing interface. The length of the field
is obtained from the source protocol length field in the mandatory
part of the NHRP header. The tuple <spi, src addr> uniquely
identifies the key and the other parameters that are used in
authentication.
The length of the authentication data field is dependent on the hash
algorithm used. The Authentication Data field contains the keyed hash
calculated over the following fields: fixed part (with hop count,
packet size and checksum being treated as if set to zero), mandatory
part, and extensions up to and including the Mobile NHC
Authentication extension.
Note that there is an explicit ordering of the extensions such that:
(a) If the Responder Address extension exists then it MUST appear
before the Authentication Extension.
(b) Any extensions that may be modified in transit (e.g., Forward
Transit Extension, Hop by Hop Authentication Extension) MUST appear
after the Mobile NHC Authentication Extension.
Calculation of the hash for this extension should allow intervening
vendor private extensions. This is in line with the mechanisms
described in RFC2002 [3]. An example of such an extension would be a
timestamp extension which would counter replay attacks. The RFC2002
authentication extensions include a timestamp. Other examples could
include new NHRP or MPOA extensions defined at a future date.
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2.2 SPI and Security Parameters Negotiation
SPI's can be negotiated either manually or using an Internet Key
Management protocol. Manual keying MUST be supported. The following
parameters are associated with the tuple <SPI, src>- lifetime,
Algorithm, Key. Lifetime indicates the duration in seconds for which
the key is valid. In case of manual keying, this duration can be
infinite. Also, in order to better support manual keying, there may
be multiple tuples active at the same time (Dst being the same).
Algorithm specifies the hash algorithm agreed upon by the two
entities. HMAC-MD5-128 [2] is the default algorithm. Other algorithms
MAY be supported by defining new values. IANA will assign the numbers
to identify the algorithm being used as described in [1].
Any Internet standard key management protocol MAY so be used to
negotiate the SPI and parameters.
2.3 Message Processing
Unauthenticated 'Mobile' Registration Request processing proceeds as
follows [1]:
- the NHC inserts the internetwork address of a serving NHS in
the 'Destination Protocol Address' field; If the NHS address
is unknown, then the NHC inserts its own internetwork address.
A 'responder address' extension is optionally added.
- the non-serving NHS forwards the packet along the routed path
based on the contents of the 'Destination Protocol Address' field.
- the serving NHS which receives the NHRP Registration Request will
set up a direct VCC to NHC after authenticating the request
- the serving NHS will then send the NHRP Registration Reply
back to the NHC on that new VCC. Note that the NHS MUST wait some
configured interval before doing this reply in order to prevent a
race condition from occuring between the VC setup and sending the
NHRP reply packet.
- the NHC will subsequently send all NHRP traffic to the serving NHS on
the direct VCC.
When the NHC adds the authentication extension header, it performs a
table looks up in order to fetch the SPI and the security parameters
based on the outgoing interface address. If there are no entries in
the table and if there is support for key management, the NHC
initiates the key management protocol to fetch the necessary
parameters. The NHC constructs the Authentication Extension payload
and calculates the hash by zeroing out the authentication data field.
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The result is placed in the authentication data field. The src
address field in the payload is the internetwork address assigned to
the outgoing interface.
If key management is not supported and authentication is mandatory,
the packet is dropped and this information is logged.
On the receiving end, the serving NHS fetches the parameters based on
the SPI and the internetwork address in the authentication extension
payload. The authentication data field is extracted before being
zeroed out in order to calculate the hash. It computes the hash on
the entire payload and if the hash does not match, then an "abnormal
event" has occurred.
The keys used by the mobile NHC for communicating with the serving
NHS in NHRP Registration Requests can be used in subsequent
resolution and purge requests made directly to the serving NHS after
receiving the NHRP Registration Reply. However, the authentication
extension defined in [1] MUST be used when these keys are applied to
resolution and purge packets.
Hop by Hop Authentication[1] and End to End authentication may be
used in combination to provide protection against both spoofing and
denial of service attacks. If only an end-to-end Mobile NHC
Authentication Extension is present, it MAY be the policy of each
transit NHS to reject the NHRP Registration Request based on the
requirement for having a Hop by Hop authentication present. Such a
requirement is a local matter.
2.4 Security Considerations
It is important that the keys chosen are strong since the security of
the entire system depends on the keys being chosen properly.
End-to-end authentication counters spoofing attacks on the home
subnet through not relying on the potentially compromised chain of
trust. The use of end-end authentication is further described in [3].
Hop-by-hop authentication prevents denial of service attacks by
introducing access control at the first point of contact to the NHRP
infrastructure.
The security of this extension is performed on an end to end basis.
The data received can be trusted only so much as one trusts the end
point entities in the path traversed. A chain of trust is established
amongst NHRP entities in the path of the NHRP Message . If the
security in an NHRP entity is compromised, then security in the
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entire NHRP domain is compromised.
Data integrity covers the entire NHRP payload up to and including the
Mobile NHC Authentication Extension. This guarantees that the data
and extensions covered by this authentication hash were not modified
and that the source is authenticated as well. If the authentication
extension is not used or if the security is compromised, then NHRP
entities are liable to both spoofing attacks, active attacks, and
passive attacks.
There is no mechanism to encrypt the messages. It is assumed that a
standard layer 3 confidentiality mechanism will be used to encrypt
and decrypt messages. It is recommended to use an Internet standard
key management protocol to negotiate the keys between the neighbors.
Transmitting the keys in clear text, if other methods of negotiation
is used, compromises the security completely.
References
[1] "NBMA Next Hop Resolution Protocol (NHRP)", Luciani, Katz, Piscitello,
Cole, Doraswamy, RFC TBD.
[2] "HMAC: Keyed Hashing for Message Authentication", Krawczyk, Bellare,
Canetti, RFC 2104.
[3] "IP Mobility Support", C.Perkins, RFC 2002.
[4] Key words for use in RFCs to Indicate Requirement Levels, S. Bradner,
RFC 2119.
Authors' Addresses
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James V. Luciani
Bay Networks
3 Federal Street
Mail Stop: BL3-03
Billerica, MA 01821
Phone: +1 978 916 4734
Email: luciani@baynetworks.com
Hiroshi Suzuki
NEC Corporation
4-1-1 Miyasaki Miyamae
Kawasaki, 216 Japan
Phone: +011 81 44 856 2123
Email: hiroshi@nwk.cl.nec.co.jp
Naganand Doraswamy
Bay Networks
3 Federal Street
Mail Stop: BL3-03
Billerica, MA 01821
Phone: +1 978 916 4734
Email: naganand@baynetworks.com
David Horton
CiTR PTY Ltd
Level 2 South Tower
339 Coronation Drive
Milton, Australia 4064
Phone: +011 61 7 32592222
Email: d.horton@citr.com.au
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