Internet Engineering Task Force Juha Heinanen
INTERNET DRAFT Telia Finland
Expires September 2000 Dave Allan
Nortel Networks
Petri Helenius
KPNQwest Finland
Arthur Lin
Shasta Networks
March 2000
PPP Internet Protocol Control Protocol Extensions for IP Subnet
<draft-helenius-ppp-subnet-00.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC 2026. Internet-Drafts are
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Abstract
The Point-to-Point Protocol (PPP) [1] provides a standard method for
transporting multi-protocol datagrams over point-to-point links. PPP
defines an extensible Link Control Protocol and a family of Network
Control Protocols (NCPs) for establishing and configuring different
network-layer protocols.
This document extends the NCP for establishing and configuring the
Internet Protocol over PPP [2] by defining an IP Subnet configuration
option.
1. Motivation
The IP-address configuration option [2] allows negotiation of a
single IP address used on the local end of a PPP link. It is
adequate when the the local end is an IP host. However, when the
local end is an router, for example an ISDN or ADSL router providing
IP connectivity for a home or small office LAN, then it should be
possible to negotiate a whole IP subnet for the LAN rather than a
single IP address for the local end of the link.
This document defines an IP subnet configuration option that allows a
router at the local end of an (unnumbered) PPP link to automatically
negotiate an IP subnet for a LAN for which it provides IP
connectivity via the PPP link. The received subnet mask will define
the subnet in combination of the IP address received from IP address
negotiation.
The following section contains the formal definition of the IP Subnet
configuration option.
2. IP Subnet IPCP Configuration Option
The IP Subnet configuration option, x (value to be assigned by IANA),
is used together with IP-address configuration option to learn an IP
subnet for a LAN attached to a router on the local end of an
(unnumbered) PPP link. The IP Subnet configuration option allows the
sender of the Configure-Request to request that the peer provides the
information. The peer MAY or MAY NOT provide the information by
ACKing or NAKing the option. The IP Subnet configuration option MAY
be present in the Configure-Nak or Configure-Ack only if the option
was present in the corresponding Configure-Request.
The format of the IP Subnet configuration option is shown below. The
fields are transmitted from left to right.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Size | Pad |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type
To be assigned.
Length
8
Size
The Size indicates the desired size of the IP subnet, i.e., how
many most significant bits of the negotiated IP-address belong to
the network part of the address. The value of the Mask MUST be
from 0 to 32. If the value of the Mask is 0, it indicates a
request for the peer to provide the Mask information. Mask value
32 denotes a single host address. Note that the sender of
Configure-Request can not propose a mask but can only indicate
that it would like to receive the mask information on Configure-
Ack. The value of the Mask in Configure-Request MUST thus always
be 0.
Pad
The Pad is used to make the length of the IP Subnet configuration
option a multiple of four octets. It MAY have any value.
Default
No IP subnet is assigned.
3. Security Considerations
The remote end of the PPP link SHOULD verify that the local end is
authorized to use the requested IP subnet information before ACKing
the request.
References
[1] Simpson, W., Editor, "The Point-to-Point Protocol (PPP)", STD 51,
RFC 1661, Daydreamer, July 1994.
[2] McGregor, G., "PPP Internet Control Protocol", RFC 1332, Merit,
May 1992.
Author Information
Juha Heinanen
Telia Finland, Inc.
Myyrmaentie 2
01600 VANTAA
Finland
jh@telia.fi
Dave Allan
Nortel Networks
P.O. Box 3511, Station 'C'
Ottawa, Ontario
CANADA, K2B 5P9
dallan@nortelnetworks.com
Petri Helenius
KPNQwest Finland
Merimiehenkatu 36
00150 HELSINKI
FINLAND
pete@kpnqwest.fi
Arthur Lin
Nortel Networks
Shasta IP Services Business Unit
4500 Great America Parkway
Santa Clara, CA 95054
U.S.A
alin@shastanets.com