Internet Engineering Task Force C. Perkins
INTERNET DRAFT IBM
10
31 May 1996
IP Encapsulation within IP
draft-ietf-mobileip-ip4inip4-02.txt
draft-ietf-mobileip-ip4inip4-03.txt
Status of This Memo
This document is a submission by the Mobile-IP Mobile IP Working Group of the
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Abstract
This document specifies a method by which an IP datagram may
be encapsulated (carried as payload) within an IP datagram.
Encapsulation is suggested as a means to alter the normal IP routing
for datagrams, by delivering them to an intermediate destination
which
that would otherwise not be otherwise selected by the (network part of the) IP destination field. This
Destination Address field in the original IP header. Encapsulation
may be done for any of serve a variety of
reasons, but is particular useful for adherence purposes, such as delivery of a datagram to the mobile-IP
specification. a
mobile node using Mobile IP.
1. Introduction
This document specifies a method by which an IP datagram may
be encapsulated (carried as payload) within an IP datagram.
Encapsulation is suggested as a means to alter the normal IP routing
for datagrams, by delivering them to an intermediate destination
which that
would otherwise not be otherwise selected based on the (network part of the)
IP Destination Address field in the original IP header. Once the
encapsulated datagram arrives at this intermediate destination node,
it is decapsulated, yielding the original IP datagram, which is then
delivered to the destination indicated by the original Destination
Address field. The process This use of encapsulation and decapsulation of a
datagram is frequently referred to as "tunneling" the datagram, and
the encapsulator and decapsulator are then considered to be the the
"endpoints" of the tunnel.
In the most general encapsulation tunneling case we have
source ---> encapsulator --------> decapsulator ---> destination
with these the source, encapsulator, decapsulator, and destination being
separate machines. nodes. The encapsulator node is considered the "entry
point" of the tunnel, and the decapsulator node is considered
the "exit point" of the tunnel. There may in general may be multiple
source-destination pairs using the same tunnel. tunnel between the
encapsulator and decapsulator.
2. Motivation
The mobile-IP Mobile IP working group has specified the use of encapsulation
as a way to deliver datagrams from a mobile host's node's "home network" to
an agent which that can deliver datagrams to the mobile host locally by conventional means [7].
to the mobile node at its current location away from home [8]. The
use of encapsulation may also be desirable whenever the source (or
an intermediate router) of an IP datagram must influence the route
by which a datagram is to be delivered to its ultimate destination.
Other possible applications of encapsulation include multicasting,
preferential billing, choice of routes with selected security
attributes, and general policy routing.
It is generally true that encapsulation and the IP loose source
routing techniques option [10] can be used in similar ways to affect the routing
of a datagram, but there are several technical reasons to prefer
encapsulation:
- There are unsolved security problems associated with the use of
the IP source routing. routing options.
- Current internet Internet routers exhibit performance problems when
forwarding datagrams which use that contain IP options, including the IP
source routing option. options.
- Too many internet hosts Many current Internet nodes process IP source routing options
incorrectly.
- Firewalls may exclude IP source-routed datagrams.
- Insertion of an IP source route option may complicate the
processing of authentication information by the source and/or
destination of a datagram, depending on how the authentication is
specified to be performed.
- It is considered impolite for intermediate routers to make
modifications to datagrams which they did not originate.
These technical advantages must be weighed against the disadvantages
posed by the use of encapsulation:
- Encapsulated datagrams typically are longer larger than source routed
datagrams.
- Encapsulation cannot be used unless it is known in advance that
the tunnel endpoint for node at the encapsulated datagram tunnel exit point can decapsulate the datagram.
Since the majority of internet hosts Internet nodes today do not perform well
when IP loose source route options are used, the second technical
disadvantage of encapsulation is not as serious as it might seem at
first.
3. IP in IP Encapsulation
An
To encapsulate an IP datagram using IP in IP encapsulation, an outer
IP header [10] is inserted before the datagram's existing IP header: header,
as follows:
+---------------------------+
| |
| Outer IP Header |
| |
+---------------------------+ +---------------------------+
| | | |
| IP Header | | IP Header |
| | | |
+---------------------------+ ====> +---------------------------+
| | | |
| | | |
| IP Payload | | IP Payload |
| | | |
| | | |
+---------------------------+ +---------------------------+
The format of the IP header is described in RFC 791[9]. The outer IP header source Source Address and destination addresses Destination Address identify
the "endpoints" of the tunnel. The inner IP header source Source Address
and destination addresses Destination Addresses identify the original sender and recipient
of the datagram. datagram, respectively. The inner IP header is not changed
by the node which encapsulates it, encapsulator, except to decrement the TTL before delivery. The inner header as noted below, and
remains unchanged during its delivery to the tunnel endpoint. exit point. No
change to IP options in the inner header occurs during delivery of
the encapsulated datagram through the tunnel. If need be, other
protocol headers such as the IP Authentication header [1] may be
inserted between the outer IP header and the inner IP header. Note
that the security options of the inner IP header (also see
section 6.3). MAY affect the
choice of security options for the encapsulating (outer) IP header.
3.1. IP Header Fields and Handling
The fields in the outer IP header are set by the encapsulator as
follows:
Version
4
IHL
The Internet Header Length measures (IHL) is the length (in bytes) of the outer IP
header exclusive of its payload, but including any
options which the encapsulating agent may insert. measured in 32-bit words [10].
TOS
The type Type of service Service (TOS) is copied from the inner IP header.
Total Length
The length Total Length measures the length of the entire encapsulated
IP datagram, including the outer IP header along
with its payload, that is to say (typically) header, the inner IP
header
header, and the original datagram. its payload.
Identification, Flags, Fragment Offset
These three fields are set in accordance with the procedures as specified in [9]. The [10]. However, if
the "Don't Fragment" bit is set in the inner IP header, it MUST
be set in the outer IP
header is copied from header; if the corresponding flag "Don't Fragment" bit is
not set in the inner IP
header. header, it MAY be set in the outer IP
header, as described in Section 5.1.
Time to Live
The Time To Live (TTL) field in the outer IP header is set to a
value appropriate for delivery of the encapsulated datagram to
the tunnel endpoint. exit point.
Protocol
The protocol field in the outer IP header is set to protocol
number
4 for the encapsulation protocol.
Header Checksum
The Internet Header Checksum is computed over the length (in bytes) checksum [10] of the outer IP header exclusive of its payload, but including any
options which the encapsulating endpoint may insert. header.
Source Address
The IP address of the encapsulating agent, encapsulator, that is, the tunnel
starting entry
point.
Destination Address
The IP address of the decapsulating agent, decapsulator, that is, the tunnel
completion exit
point.
Options
not copied from
Any options present in the inner IP header are in general NOT
copied to the outer IP header. However, new options
particular specific
to the tunnel path MAY be added. In particular, any supported flavors
types of security options of the inner IP header MAY affect the
choice of security options for the tunnel. outer header. It is not
expected that there be a one-to-one mapping of such options to
the options or security headers selected for the tunnel.
The inner
When encapsulating a datagram, the TTL in the inner IP header
is decremented by one. one if the tunneling is being done as part of
forwarding the datagram; otherwise, the inner header TTL is not
changed during encapsulation. If the resulting TTL in the inner IP
header is 0, the datagram is not tunneled. discarded and an ICMP Time Exceeded
message SHOULD be returned to the sender. An encapsulating agent encapsulator MUST NOT
encapsulate a datagram with TTL = 0 for delivery to a tunnel
endpoint. 0.
The TTL in the inner IP header is not changed when decapsulating.
If, after decapsulation, the inner datagram has TTL zero, a tunnel endpoint = 0, the
decapsulator MUST discard the datagram. If If, after decapsulation, the
decapsulator forwards the datagram to some one of its network interface, interfaces,
it will decrement the TTL as a result of doing normal IP forwarding.
See also subsection Section 4.4.
The encapsulating agent is free to encapsulator may use any existing IP mechanisms appropriate for
delivery of the encapsulated payload to the tunnel
endpoint. exit point. In
particular, this means that use of IP options is allowed, and use of fragmentation are allowed,
is allowed unless the "Don't Fragment" bit is set in the inner IP
header. This restriction on fragmentation is required so that hosts nodes
employing Path MTU discovery [6] Discovery [7] can obtain the information they
seek.
3.2. Routing Failures
Routing loops within a tunnel are particularly dangerous when
they cause datagrams to arrive again at the encapsulator. Suppose
a datagram arrives at a router for forwarding, and the router
determines that the datagram has to be encapsulated before further
delivery. Then:
- If the IP Source Address of the datagram matches the router's own
IP address on any of its network interfaces, an implementation the router MUST NOT further encapsulate.
tunnel the datagram; instead, the datagram SHOULD be discarded.
- If the IP Source Address of the datagram matches the IP address
of the tunnel
destination, an implementation SHOULD destination (the tunnel exit point is typically
chosen by the router based on the Destination Address in the
datagram's IP header), the router MUST NOT further encapsulate. tunnel the datagram;
instead, the datagram SHOULD be discarded.
See also subsection Section 4.4.
4. ICMP messages Messages from within the tunnel Tunnel
After an encapsulated datagram has been sent, the encapsulating
agent encapsulator may
receive an ICMP [8] [9] message from any intermediate router within the tunnel, except for
tunnel other than the tunnel endpoint. exit point. The action taken by the encapsulating agent
encapsulator depends on the type of ICMP message received. When the
received message contains enough information, the
encapsulating agent may encapsulator MAY
use the incoming message to create a similar ICMP message, to be sent
to the originator of the inner original unencapsulated IP datagram. datagram (the
original sender). This process will be referred to as "relaying" the
ICMP message to from the source tunnel.
ICMP messages indicating an error in processing a datagram include a
copy of (a portion of) the original unencapsulated datagram. datagram causing the error. Relaying an
ICMP message requires that the encapsulator must strip off the outer IP
header which it receives from the sender this returned copy of the ICMP message. original datagram. For cases where
in which the received ICMP message does not contain enough data, data to
relay the message, see
section Section 5.
4.1. Destination Unreachable (Type 3)
ICMP Destination Unreachable messages are handled by the encapsulator
depending upon their
type. Code field. The model suggested here allows
the tunnel to "extend" a network to include non-local (e.g., mobile) hosts.
nodes. Thus, if the original destination in the unencapsulated
datagram is on the same network as the encapsulating agent, encapsulator, certain
Destination Unreachable
codes Code values may be modified to conform to the
suggested model.
Network Unreachable (Code 0)
A
An ICMP Destination Unreachable message may SHOULD be returned
to the original sender. If the original destination in
the unencapsulated datagram is on the same network as the encapsulating agent,
encapsulator, the newly generated Destination Unreachable
message sent by the encapsulating agent encapsulator MAY have
code Code 1 (Host
Unreachable), since presumably the datagram arrived to at the
correct network and the encapsulating agent encapsulator is trying to create the
appearance that the original destination is local to that
network even if it's it is not. Otherwise, if the encapsulating agent
must return encapsulator
returns a Destination Unreachable with code 0 message to message, the original sender. Code field MUST
be set to 0 (Network Unreachable).
Host Unreachable (Code 1)
The encapsulating agent must encapsulator SHOULD relay Host Unreachable messages to the source
sender of the original unencapsulated datagram. datagram, if possible.
Protocol Unreachable (Code 2)
When the encapsulating agent encapsulator receives a an ICMP Protocol Unreachable
ICMP
message, it should SHOULD send a Destination Unreachable message with code
Code 0 or 1 (see the discussion for code Code 0) to the sender of
the original unencapsulated datagram. Since the original
sender might only rarely did not use protocol 4, 4 in sending the datagram, it would
be usually be meaningless to return code Code 2 to that sender.
Port Unreachable (Code 3)
This code Code should never be received by the encapsulating
agent, encapsulator, since
the outer IP header does not refer to any port number. It must not MUST
NOT be relayed to the source sender of the original unencapsulated
datagram.
Datagram Too Big (Code 4)
The encapsulating agent must encapsulator MUST relay ICMP Datagram Too Big messages to
the source sender of the original unencapsulated datagram.
Source Route Failed (Code 5)
This code should Code SHOULD be treated handled by the encapsulating agent encapsulator itself.
It must not MUST NOT be relayed to the source sender of the original
unencapsulated datagram.
4.2. Source Quench (Type 4)
The encapsulating agent encapsulator SHOULD NOT relay ICMP Source Quench messages to the source
sender of the original unencapsulated datagram, but instead SHOULD
activate whatever congestion control mechanisms it implements to help
alleviate the congestion detected within the tunnel.
4.3. Redirect (Type 5)
The encapsulating agent may act on encapsulator MAY handle the ICMP Redirect message if it is
possible, but it should messages itself.
It MUST NOT not relay the Redirect back to the source sender of the datagram which was encapsulated. original
unencapsulated datagram.
4.4. Time Exceeded (Type 11)
ICMP Time Exceeded messages report (presumed) routing loops
within the tunnel itself. Reception of Time Exceeded messages by
the encapsulator MUST be reported to the originator sender of the original
unencapsulated datagram as Host Unreachable (Type 3 3, Code 1). Host
Unreachable is preferable to Network Unreachable; since the datagram
was handled by the encapsulator, and the encapsulator is often
considered to be on the same network as the destination address in
the original unencapsulated datagram, then the datagram is considered
to have reached the correct network, but not the correct destination
host
node within that network.
4.5. Parameter Problem (Type 12)
If the parameter problem Parameter Problem message points to a field copied from the
original unencapsulated datagram, the encapsulating agent may encapsulator MAY relay the
ICMP message to the source; sender of the original unencapsulated datagram;
otherwise, if the problem occurs with an IP option inserted by
the encapsulating agent, encapsulator, then the encapsulating
agent must not encapsulator MUST NOT relay the ICMP
message to the source. original sender. Note that an
encapsulating agent encapsulator following
prevalent current practice will never insert any IP options into the
encapsulated datagram, except possibly for security reasons.
4.6. Other messages ICMP Messages
Other ICMP messages are not related to the encapsulation operations
described within this protocol specification, and should be acted on
by the encapsulator as specified in [8]. [9].
5. Tunnel Management
Unfortunately, ICMP only requires IP routers to return 8 bytes octets
(64 bits) of the datagram beyond the IP header. This is not enough
to include a copy of the encapsulated (inner) IP header, so it is not
always possible for the
home agent encapsulator to immediately reflect relay the ICMP message from
the interior of a tunnel back to the originating host. original sender.
However, by carefully maintaining "soft state" about its tunnels, tunnels into
which it sends, the encapsulating router encapsulator can return accurate ICMP messages to
the original sender in most cases. The router encapsulator SHOULD maintain
at least the following soft state information about each tunnel:
- MTU of the tunnel (subsection (Section 5.1)
- TTL (path length) of the tunnel
- Reachability of the end of the tunnel
The router encapsulator uses the ICMP messages it receives from the interior
of a tunnel to update the soft state information for that tunnel.
ICMP errors that could be received from one of the routers along the
tunnel interior include:
- Datagram Too Big
- Time Exceeded
- Destination Unreachable
- Source Quench
When subsequent datagrams arrive that would transit the tunnel,
the router encapsulator checks the soft state for the tunnel. If the
datagram would violate the state of the tunnel (such as, (for example, the TTL
of the new datagram is less than the tunnel "soft state" TTL) the router
encapsulator sends an ICMP error message back to the
source, sender of the
original datagram, but also forwards encapsulates the datagram and forwards it
into the tunnel.
Using this technique, the ICMP error messages sent by encapsulating
routers the
encapsulator will not always match up one-to-one with errors
encountered within the tunnel, but they will accurately reflect the
state of the network.
Tunnel soft state was originally developed for the IP address
encapsulation Address
Encapsulation (IPAE) specification [4].
5.1. Tunnel MTU Discovery
When the Don't Fragment bit is set by the originator and copied into
the outer IP header, the proper MTU of the tunnel will be learned
from ICMP Datagram Too Big (Type 3 3, Code 4) "Datagram Too Big" errors messages reported to
the encapsulator. To support originating hosts sending nodes which use this capability, Path MTU
Discovery, all encapsulator implementations MUST support Path MTU
Discovery [5, 6] 7] soft state within their tunnels. In this particular
application
application, there are several advantages:
- As a benefit of Tunnel Path MTU Discovery, Discovery within the tunnel, any
fragmentation which occurs because of the size of the
encapsulation header is performed only once after encapsulation.
This prevents multiple fragmentation of a single datagram, which
improves processing efficiency of the path routers decapsulator and tunnel decapsulator. the
routers within the tunnel.
- If the source of the unencapsulated datagram is doing Path MTU
discovery
Discovery, then it is desirable for the encapsulator to know
the MTU to the decapsulator. If it doesn't know the MTU then it
can transfer the DF bit to of the outer datagram; however, if that
triggers tunnel. Any ICMP Datagram Too Big messages from
within the tunnel (and hence are returned to the encapsulator) encapsulator, and as noted
in Section 5, it is not always possible for the encapsulator cannot always
return a correct to
relay ICMP response messages to the source unless it has kept
state information of the original unencapsulated
datagram. By maintaining "soft state" about recently sent datagrams. If the tunnel MTU is returned to of the source by
tunnel, the encapsulator in a can return correct ICMP Datagram Too Big message,
messages to the original sender of the unencapsulated datagram to
support its own Path MTU Discovery. In this case, the MTU that
is conveyed to the original sender by the encapsulator SHOULD
be the MTU of the tunnel minus the size of the encapsulating
IP header. This will avoid fragmentation of the original IP
datagram by the
encapsulator, something that is otherwise certain to occur. encapsulator.
- If the source of the original unencapsulated datagram is
not doing Path MTU discovery Discovery, it is still desirable for the
encapsulator to know the MTU to of the decapsulator. tunnel. In
particular particular, it is
much better to fragment the inner original datagram when encapsulating,
than to allow the outer encapsulated datagram to be fragmented.
Fragmenting the
inner original datagram can be done by the encapsulator
without special buffer requirements and without the need to
keep reassembly state in the decapsulator. By contrast contrast, if
the outer encapsulated datagram is fragmented fragmented, then the decapsulator needs to keep
must reassemble the fragmented (encapsulated) datagram before
decapsulating it, requiring reassembly state and buffer space on behalf of
within the decapsulator.
Thus, the destination.
The encapsulator SHOULD in normal circumstances normally do Path MTU discovery
and try Discovery,
requiring it to send all datagrams into the tunnel with the DF "Don't
Fragment" bit set. set in the outer IP header. However there are
problems with this approach. When the source original sender sets the DF bit it
"Don't Fragment" bit, the sender can react quickly to resend the information if it gets a any returned
ICMP Datagram Too Big. When Big error message by retransmitting the original
datagram. On the other hand, suppose that the encapsulator gets a receives
an ICMP Datagram Too Big, but Big message from within the
source tunnel. In that
case, if the original sender of the unencapsulated datagram had
not set the DF "Don't Fragment" bit, then there is nothing sensible that
the encapsulator can do to let the source know. original sender know of the
error. The encapsulator MAY keep a copy of the sent datagram
whenever it tries increasing the MTU
- this will tunnel MTU, in order to allow it
to fragment and resend the datagram fragmented if it gets a
datagram too big Datagram Too Big
response. Alternatively the encapsulator MAY be configured for
certain classes types of input to datagrams not to set the DF "Don't Fragment" bit when
the source original sender of the unencapsulated datagram has not set the DF
"Don't Fragment" bit.
5.2. Congestion
Tunnel soft state will collect
An encapsulator might receive indications of congestion, such as
an congestion from the
tunnel, for example, by receiving ICMP (Type 4) Source Quench or messages from
nodes within the tunnel. In addition, certain link layers and
various protocols not related to the Internet suite of protocols
might provide such indications in the form of a Congestion
Experienced flag [6] flag. The encapsulator SHOULD reflect conditions of
congestion in
datagrams from its "soft state" for the decapsulator (tunnel peer). When tunnel, and when subsequently
forwarding
another datagram datagrams into the tunnel, it is appropriate to the encapsulator SHOULD use approved
appropriate means for controlling congestion [3]; However, the
encapsulator SHOULD NOT send ICMP Source Quench messages SHOULD
NOT be sent to the originator.
original sender of the unencapsulated datagram.
6. Security Considerations
IP encapsulation potentially reduces the security of the Internet.
For this reason Internet,
and care needs to be taken in the implementation and
deployment.
Assume an organization has good physical control deployment of a secure subset
of its network. Assume that the
IP encapsulation. For example, IP encapsulation makes it difficult
for border routers connecting that secure
network do not allow in datagrams with source addresses belonging to
interfaces filter datagrams based on that secure network. header fields. In that situation it is possible
to safely deploy protocols within that network which depend on
particular, the
source address original values of datagrams for authentication purposes.
Networks with physical security can still be used to run protocols
which are convenient, but which have implementation or protocol bugs
which would make them dangerous to use if external sources have
access to the protocol. The external sources can be excluded using
router datagram filtering.
IP encapsulation protocols may allow datagrams to bypass the checks Source Address, Destination
Address, and Protocol fields in the border routers. There are two cases to consider:
- The case where IP header, and the people controlling port numbers
used in any transport header within the border routers datagram, are
trying to protect inner machines from themselves.
- The case where not located
in their normal positions within the inner machine is looking datagram after its own
defense.
An uncooperative inner machine cannot be protected by the border
router except by barring all packets to that machine. There is
nothing to stop encapsulated encapsulation.
Since any IP coming in to that inner machine in
otherwise harmless datagrams such as port 53 UDP datagrams (i.e.,
apparently DNS datagrams). So there is a strong case for placing
the security controls at the host rather than the router. However,
in situations where the administrative control of the inner machine
is cooperative but lacks thoroughness or competence, security datagram can be
enhanced by also putting protection in the encapsulated and passed through a
tunnel, such filtering border routers. routers need to carefully examine all
datagrams.
6.1. Router Considerations
Routers need to be aware of IP encapsulation protocols so they can in order
to correctly filter incoming datagrams.
Beyond that it It is desirable that
such filtering be integrated with IP authentication [1]. In the case of Where IP encapsulation this can have
2 forms: Encapsulation
authentication is used, encapsulated packets might be allowed (in some cases) as long
as to
enter an organization when the encapsulating datagrams authentically come from an expected
encapsulator. Alternatively encapsulation might be allowed if (outer) packet or the
encapsulated (inner) packet is sent by an authenticated, trusted
source. Encapuslated packets containing no such authentication
represent a potentially large security risk.
IP datagrams have authentication.
Data which is are encapsulated and encrypted [2] may might also
pose a problem. problem for filtering routers. In this case case, the router can only
filter the datagram only if it knows shares the security association. association used
for the encryption. To allow this sort of encryption in environments where
in which all packets need to be filtered (or at least accounted for) for),
a mechanism must be in place for the receiving host node to securely
communicate the security association to the border router. This
might, more rarely, also apply to the security association used for
outgoing datagrams.
6.2. Host Considerations
Receiving
Host implementations that are capable of receiving encapsulated IP encapsulation software SHOULD classify incoming
datagrams and SHOULD admit only allow those datagrams fitting into one or more
of the following categories:
- The protocol is harmless: source address based address-based authentication is
not needed.
- The encapsulating (outer) datagram can be comes from an authentically
identified, trusted because source. The authenticity of trust in the authentically
identified encapsulating host. That authentic identification source could come from
be established by relying on physical security plus in addition to
border router
configuration configuration, but is more likely to come from AH authentication. use
of the IP Authentication header [1].
- The inner encapuslated (inner) datagram includes an IP Authentication
header.
- The encapsulated (inner) datagram is addressed to a network
interface belonging to the decapsulator, or to a node with which
the decapsulator has AH authentication. entered into a special relationship for
delivering such encapsulated datagrams.
Some or all of this checking could be done in border routers rather
than the receiving host node, but it is better if border router checks are
used as backup backup, rather than being the only check.
6.3. Using Security Options
The security options of the inner IP header MAY affect the choice of
security options for the encapsulating IP header.
7. Acknowledgements
Parts of sections Sections 3 and 5 of this document were taken from sections portions
(authored by Bill Simpson) of earlier versions of the mobile-IP Mobile IP
Internet Draft [7]. [8]. The original text for section 6 (Security
Considerations) was contributed by Bob Smart. Good ideas have also
been included from RFC 1853 [10], [11], also authored by Bill Simpson. "Security Considerations"
(section 6) was largely contributed by Bob Smart.
Thanks also to Anders Klemets for finding mistakes and suggesting
improvements to the draft. Finally, thanks to David Johnson for
going over the draft with a fine-toothed comb, finding mistakes,
improving consistency, and making many other improvements to the
draft.
References
[1] R. Atkinson. IP Authentication Header. RFC 1826, August 1995.
[2] R. Atkinson. IP Encapsulating Security Payload. RFC 1827,
August 1995.
[3] F. Baker, Editor. Requirements for IP Version 4 Routers. RFC
1812, June 1995.
[4] R. Gilligan, E. Nordmark, and B. Hinden. IPAE: The SIPP
Interoperability and Transition Mechanism. Internet Draft --
work in progress, March 1994.
[5] S. Knowles. IESG Advice from Experience with Path MTU
Discovery. RFC 1435, March 1993.
[6] A. Mankin and K. Ramakrishnan. Gateway Congestion Control
Survey. RFC 1254, August 1991.
[7] J. Mogul and S. Deering. Path MTU Discovery. RFC 1191,
November 1990.
[7]
[8] C. Perkins, Editor. ietf-draft-mobileip-protocol-16.txt - work
in progress. IPv4 Mobility Support, April Support.
ietf-draft-mobileip-protocol-17.txt (work in progress), May 1996.
[8]
[9] J. B. Postel, Editor. Internet Control Message Protocol. RFC
792, September 1981.
[9]
[10] J. B. Postel, Editor. Internet Protocol. RFC 791, September
1981.
[10]
[11] W. Simpson. IP in IP Tunneling. RFC 1853, October 1995.
Author's Address
Questions about this memo can be directed to:
Charles Perkins
Room H3-D34
T. J. Watson Research Center
IBM Corporation
30 Saw Mill River Rd.
Hawthorne, NY 10532
Work: +1-914-784-7350
Fax: +1-914-784-6205
E-mail: perk@watson.ibm.com
The working group can be contacted via the current chairs: chair:
Jim Solomon Tony Li
Motorola, Inc. cisco systems
1301 E. Algonquin Rd. 170 W. Tasman Dr.
Schaumburg, IL 60196 San Jose, CA 95134
Work: +1-847-576-2753 Work: +1-408-526-8186
E-mail: solomon@comm.mot.com E-mail: tli@cisco.com