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RFC2336 - Classical IP to NHRP Transition

王朝other·作者佚名  2008-05-31
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Network Working Group J. LUCiani

Request for Comments: 2336 Bay Networks

Category: Informational July 1998

Classical IP and ARP over ATM to NHRP Transition

Status of this Memo

This memo provides information for the Internet community. It does

not specify an Internet standard of any kind. Distribution of this

memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (1998). All Rights Reserved.

Abstract

This document describes methods and procedures for the graceful

transition from an ATMARP LIS[1] to an NHRP LIS[2] network model over

ATM.

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 [6].

ATMARP defines an initial application of classical IP and ARP in an

ATM network environment configured as a LIS[1]. ATMARP only

considers application of ATM as a direct replacement for the "wires"

and local LAN segments connecting IP end-stations and routers

operating in the "classical" LAN-based paradigm.

The NBMA Next Hop Resolution Protocol (NHRP) allows a source station

(a host or router), wishing to communicate over a Non-Broadcast,

Multi-Access (NBMA) subnetwork, to determine the internetworking

layer addresses and NBMA addresses of suitable "NBMA next hops"

toward a destination station. If the destination is connected to the

NBMA subnetwork and direct communication is administratively allowed,

then the NBMA next hop is the destination station itself. Otherwise,

the NBMA next hop is the egress router from the NBMA subnetwork that

is "nearest" to the destination station. For the purposes of this

document, the NBMA network is of type ATM.

It is reasonable to eXPect that ATMARP Clients and NHRP Clients will

initially coexist within a LIS. Thus, it is necessary to define a

graceful transition, including a period of coexistance, from the use

of ATMARP to the use of NHRP for address resolution in the LIS

[1][2]. In short, NHSs will be required to respond to ATMARP Client

queries in a fashion which will permit continued use of the ATMARP

Client within the LIS during the ATMARP to NHRP transition period.

Note that this document places no protocol requirements upon

ATMARP[1] servers.

For the following, it will be assumed that the reader is familiar

with the terminology as described in [1][2][3].

2. Service Requirements

If NHRP is to be used in a LIS then only NHSs will be used in the

LIS; that is, there will not be a mixture of NHSs and ATMARP servers

within the same LIS. Since ATMARP servers will not be able to

understand NHCs and since, as described below, NHSs will respond to

ATMARP Clients, this is a reasonable simplifying restriction.

This document will only address SVC based environments and will not

address PVC environments. This document will refer only to ATM AAL5

as the NBMA and IP as the protocol layer since ATMARP only addresses

these protocols.

2.1 NHRP Server Requirements

If NHRP Servers (NHS) are to be deployed in a LIS which contains both

ATMARP Clients and NHRP Clients then NHSs MUST respond to

ATMARP_Requests sent by ATMARP Clients in the same fashion that an

ATMARP Server would respond as described in [1]. To do this, the NHS

MUST first recognize the LLC/SNAP ATMARP code point with LLC=0xAA-

AA-03, OUI=0x00-00-00, and ethertype=0x08-06. Further, the NHS MUST

recognize the packet formats described in Section 8.7 of [1].

However, since this document does not extend to PVC environments,

NHSs MUST only receive/respond to values of ar$op of 1,2,10

(Decimal). If an NHS receives an ATMARP message with ar$op values

other than those previously noted then the NHS MUST discard the

packet and MUST NOT take any further action.

When an NHS receives a valid (as defined in the previous paragraph)

ATMARP_Request packet, the NHS MUST follow the rules described in

Section 8.4 of [1] with the following additional processing:

1) When an ATMARP_Request causes a new table entry in the NHS for

an ATMARP Client, that table entry MUST be marked as being of

type "ATMARP" so that it can be differentiated from an NHRP

sourced entry.

2) An ATMARP_Request MUST NOT cause an ATMARP_Reply to be sent if

that ATMARP_Request contains an off-LIS protocol address. This

should never happen because the IP stack on the requesting

machine should automatically send the packet to the default

router. If this does occur then the ATMARP_Request MUST cause

an ATMARP_NAK to be sent to the originator.

In [1], an ATMARP_Request packet also serves as a

registraion/registration-update packet which would cause a server to

add an entry to a server's cache or to update a previously existing

entry. When an NHS receives an ATMARP_Request which causes the

creation of a new cache entry in the NHS or updates an existing entry

then that cache entry will have a holding time of 20 minutes (this is

the default value in [1]).

An NHS receiving an NHRP Resolution Request MUST NOT send a positive

NHRP Resolution Reply for a station which registered via ATMARP if

the station sending the NHRP Resolution Request is outside the LIS of

the station which registered itself via ATMARP. This is because the

station which registered via ATMARP is almost certainly not prepared

to accept a cut-through. When this occurs, the replying NHS must

send NHRP Resolution Reply which contains a CIE code of "4 -

Administratively Prohibited" as described in [2]. This type of reply

does not preclude the station sending the NHRP Resolution Request

from sending its data packets along the routed path but it does

preclude that station from setting up a cut-through VC.

2.2 Multi-server environments

Since NHRP servers may work in a multi-server environment on a per

LIS basis during the transition, it is necessary to know how cache

synchronization occurs. These rules may be found in [5].

3. Security Considerations

Not all of the security issues relating to IP over ATM are clearly

understood at this time, due to the fluid state of ATM

specifications, newness of the technology, and other factors.

It is believed that ATM and IP facilities for authenticated call

management, authenticated end-to-end communications, and data

encryption will be needed in globally connected ATM networks. Such

future security facilities and their use by IP networks are beyond

the scope of this memo.

There are known security issues relating to host impersonation via

the address resolution protocols used in the Internet [4]. No

special security mechanisms have been added to ATMARP. While NHRP

supplies some mechanisms for authentication, ATMARP does not. Since

any security mechanism is only as good as its weakest link, it should

be assumed that when NHRP and ATMARP exist with a given LIS, the

security of a combination is only as good as that supplied by ATMARP.

References

[1] Laubach, M. and J. Halpern, "Classical IP and ARP over ATM", RFC

2225, April 1998.

[2] Luciani, J., Katz, D., Piscitello, D., Cole, B. and N. Doraswamy,

"NBMA Next Hop Resolution Protocol (NHRP)", RFC2332, April 1998.

[3] Luciani, J., Armitage, G., Halpern, J. and N. Doraswamy, "Server

Cache Synchronization Protocol (SCSP)", RFC2334, April 1998.

[4] Security Problems in the TCP/IP Protocol Suite, Bellovin, ACM

Computer Communications Review, Vol. 19, Issue 2, pp. 32-48, 1989.

[5] Luciani, J., "A Distributed NHRP Service Using SCSP", RFC2335,

April 1998.

[6] Bradner, S., "Key words for use in RFCs to Indicate Requirement

Levels", RFC2119, March 1997.

Acknowledgments

Thanks to Andy Malis for his input on this draft.

Author's Addresses

James V. Luciani

Bay Networks

3 Federal Street

Mail Stop: BL3-03

Billerica, MA 01821

Phone: +1 978 916 4734

Email: luciani@baynetworks.com

Full Copyright Statement

Copyright (C) The Internet Society (1998). All Rights Reserved.

This document and translations of it may be copied and furnished to

others, and derivative works that comment on or otherwise explain it

or assist in its implementation may be prepared, copied, published

and distributed, in whole or in part, without restriction of any

kind, provided that the above copyright notice and this paragraph are

included on all such copies and derivative works. However, this

document itself may not be modified in any way, such as by removing

the copyright notice or references to the Internet Society or other

Internet organizations, except as needed for the purpose of

developing Internet standards in which case the procedures for

copyrights defined in the Internet Standards process must be

followed, or as required to translate it into languages other than

English.

The limited permissions granted above are perpetual and will not be

revoked by the Internet Society or its successors or assigns.

This document and the information contained herein is provided on an

"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING

TASK FORCE DISCLAIMS 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.

 
 
 
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