draft-ietf-dhc-csr-01.txt   draft-ietf-dhc-csr-02.txt 
Network Working Group Ted Lemon Network Working Group Ted Lemon
Internet Draft Nominum, Inc. Internet Draft Nominum, Inc.
Obsoletes: draft-ietf-dhc-csr-00.txt March, 2000 Obsoletes: draft-ietf-dhc-csr-01.txt June, 2000
Expires September 2000 Expires January 2001
The Classless Static Route Option for DHCP The Classless Static Route Option for DHCP
<draft-ietf-dhc-csr-01.txt> <draft-ietf-dhc-csr-02.txt>
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026. all provisions of Section 10 of RFC2026.
This document is an Internet-Draft. Internet-Drafts are working This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts. working documents as Internet-Drafts.
skipping to change at line 164 skipping to change at line 163
Subnet number Subnet mask Destination descriptor Subnet number Subnet mask Destination descriptor
0 0 0 0 0 0
10.0.0.0 255.0.0.0 8.10 10.0.0.0 255.0.0.0 8.10
10.17.0.0 255.255.0.0 16.10.17 10.17.0.0 255.255.0.0 16.10.17
10.27.129.0 255.255.255.0 24.10.27.129 10.27.129.0 255.255.255.0 24.10.27.129
10.229.0.128 255.255.255.128 25.10.229.0.128 10.229.0.128 255.255.255.128 25.10.229.0.128
10.198.122.47 255.255.255.255 32.10.198.122.47 10.198.122.47 255.255.255.255 32.10.198.122.47
DHCP Client Behavior DHCP Client Behavior
The DHCP client MAY use this option to install a set of static DHCP clients that do not support this option MUST ignore it if it
routes in its routing table. A DHCP client that implements this is received from a DHCP server. DHCP clients that support this
option SHOULD use this option in preference to the Static routes option MUST install the routes specified in the option.
option if both are present in a reply from the DHCP server. The
client MAY request both options. DHCP clients that support this option and that send a DHCP
Parameter Request List option MUST request both this option and
the Routers option [2] in the DHCP Parameter Request List.
If the DHCP server returns a Routers option, clients that support
the Classless Static Routes option MUST use the default route(s)
listed in the Routers option in addition to the routes listed
in the Classless Static Routes option.
After deriving a subnet number and subnet mask from each After deriving a subnet number and subnet mask from each
destination descriptor, the DHCP client SHOULD check each route to destination descriptor, the DHCP client SHOULD check each route to
determine if are any bits in the destination network number whose determine if are any bits in the destination network number whose
value is one whose corresponding value in the subnet mask is zero, value is one whose corresponding value in the subnet mask is zero,
and SHOULD NOT install any routes for which this is the case. For and SHOULD NOT install any routes for which this is the case. For
example, the client should not install a route with a destination example, the client should not install a route with a destination
of 129.210.377.4 and a subnet mask of 255.255.255.0. of 129.210.377.4 and a subnet mask of 255.255.255.128.
Because a full routing table can be quite large, the standard 576 Because a full routing table can be quite large, the standard 576
octet maximum size for a DHCP message may be too short to contain octet maximum size for a DHCP message may be too short to contain
some legitimate Classless Static Route options. Because of this, some legitimate Classless Static Route options. Because of this,
clients implementing the Classless Static Route option SHOULD send clients implementing the Classless Static Route option SHOULD send
a Maximum DHCP Message Size [2] option if the DHCP client's TCP/IP a Maximum DHCP Message Size [2] option if the DHCP client's TCP/IP
stack is capable of reassembling fragmented IP datagrams. In this stack is capable of reassembling fragmented IP datagrams. In this
case, the client SHOULD set the value of this option to the MTU of case, the client SHOULD set the value of this option to the MTU of
the interface that the client is configuring. the interface that the client is configuring.
DHCP Server administrator responsibilities DHCP Server administrator responsibilities
The client's behaviour if both a Routers option and a Classless Many clients may not implement the Classless Static Routes option.
Static Routes option default route (network number 0.0.0.0, network DHCP server administrators should therefore configure their DHCP
mask 0.0.0.0) are specified is not defined in this document, so as servers to send both a Routers option and a Classless Static
to avoid placing onerous requirements on the client and server Routes option, and should specify all default routes in the Routers
implementations. Therefore, the DHCP server administrator SHOULD option, and not specify any default routes in the Classless
NOT configure the DHCP server so that it sends both a Routers Static Routes option.
option and a Classless Static Routes option containing a default
route. Either no Routers option should be configured (this is
probably preferable in the near term, since only newer DHCP clients
will implement this option), or the Classless Static Routes option
should not contain a default route.
The client's behaviour is also not defined in the case where the
server sends a classless static route in which some bits in the
network number are 1, and corresponding bits in the subnet mask are
zero. Therefore, DHCP server administrators SHOULD NOT configure
the DHCP server to send such a route.
Security Considerations Security Considerations
DHCP currently provides no authentication or security mechanisms. DHCP currently provides no authentication or security mechanisms.
Potential exposures to attack are discussed in section 7 of the DHCP Potential exposures to attack are discussed in section 7 of the DHCP
protocol specification [1]. The Classless Static Routes option can protocol specification [1]. The Classless Static Routes option can
be used to misdirect network traffic by providing incorrect IP be used to misdirect network traffic by providing incorrect IP
addresses for routers. addresses for routers.
References References
skipping to change at line 249 skipping to change at line 244
Author Information Author Information
Ted Lemon Ted Lemon
Nominum, Inc. Nominum, Inc.
950 Charter Street 950 Charter Street
Redwood City, CA 94043 Redwood City, CA 94043
email: Ted.Lemon@nominum.com email: Ted.Lemon@nominum.com
Expiration Expiration
This document will expire on July 31, 2000. This document will expire on January 31, 2001.
Full Copyright Statement Full Copyright Statement
Copyright (C) The Internet Society (2000). All Rights Reserved. Copyright (C) The Internet Society (2000). All Rights Reserved.
This document and translations of it may be copied and furnished to This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are kind, provided that the above copyright notice and this paragraph are
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