draft-ietf-issll-rsvp-cap-01.txt
Internet Draft Syed, Hamid,
draft-ietf-issll-rsvp-cap-01.txt Nortel Networks
November, 2000
Capability Negotiation: The RSVP CAP Object
Status of this Memo
This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Task
Force (IETF), its areas, and its working groups. Note that other groups
may also distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet- Drafts as reference material
or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Distribution of this memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
1. Abstract
The DCLASS object is proposed in [DCLASS] to represent and carry
Differentiated Services Code Points (DSCPs) within RSVP messages. The
principle use of the DCLASS object is to carry DSCP information
between a DS network and upstream nodes that may wish to mark packets
with DSCP values. A network element in the DS network determines the
value for DSCP which is further carried as a DCLASS object in RSVP
RESV message to the sender host.
There may be situations where the sender host is not capable or may
not wish to mark the packets. Currently, there is no way for the
host or network devices to specify their capabilities to the downstream
nodes.
This draft proposes a capability object (CAP object) in the RSVP PATH
message that can be used to convey end host/upstream node
capabilities to the downstream network. It also defines one bit in the
CAP field of the CAP object to convey the host/upstream node's
Hamid Expires May, 2001 [Page 1]
draft-ietf-issll-rsvp-cap-01.txt November, 2000
marking capability/willingness for accepting a DCLASS object from the
downstream network and marking the downstream packets.
2. Introduction
The mechanics of using RSVP [RSVP] signalling and the DCLASS object
for requesting and applying the QoS in a differentiated services [DS]
network is described fully in [INTDIFF]. It assumes an architecture
with RSVP senders and receivers and a differentiated services network
somewhere between the sender and the receiver. At least one RSVP aware
network element resides in the diff-serv network. This network element
interacts with RSVP messages arriving from outside the DS network.
The principle use of the DCLASS object is to carry DSCP information
between a DS network and upstream nodes that may wish to mark packets
with DSCP values. A network element in the DS network determines the
value for DSCP which is further carried as a DCLASS object in RSVP
RESV message to the sender host. If the network element determines
that the request represented by the PATH and RESV messages is
admissible to the diff-serv network, a desision is made to mark the
arriving data packets for this traffic using MF classification, or
to request upstream marking of packets with the appropriate DSCPs.
If the network element decides the packets to be marked at the sender
host for the data traffic, it adds a DCLASS object in the RSVP RESV
message to the host. The use and format of DCLASS object is fully
specified in [DCLASS].
There may be situations where the sender host is not capable or may
not wish to mark the packets. In the current definition of DCLASS
object, the network edge device inserts the DCLASS object in the RSVP
RESV message without having any prior knowledge of the host capability
whether or not the host can make use of this object. This is one
example where the network element needs to know the host capabilities
before making a policy decision. Moreover, the definition of DCLASS
object allows any DS domain to supply DCLASS object on a flow to the
upstream DS domains. A prior knowledge of the upstream DS domain's
marking capability could be useful for the downstream DS domain. There
could be other scenerios where an advance knowledge of the host or a
upstream node's capability may help the network to provide better
policy decisions to the end host. Currently, there is no way for the
host or network devices to specify their capabilities.
The decision where the data packets should be marked can be made at the
DS network nodes assuming that the network edge devices have a prior
knowledge of the marking capability of the upstream domains.
Section 3 of this draft describes two scenarios to explain the use of
CAP object in RSVP PATH message.
3. Capability Negotiation
The capability object called 'CAP' object can be used as a mechanism
for conveying node capabilities or willingness in RSVP messages. As an
example, we will focus on the marking capability of nodes throughout
this document and define a single bit for host marking information to
be carried in the CAP field inside the CAP object of RSVP PATH message.
Hamid Expires May, 2001 [Page 2]
draft-ietf-issll-rsvp-cap-01.txt November, 2000
However, the CAP is a generic object that can be used to carry any other
meaningful capability information in the RSVP PATH message. To explain
the use of CAP object in RSVP PATH message, we will describe two
scenarios
- Host-Edge router interaction
- Border Router-Border Router interaction
It should be noted that how and when the packets will be marked is a
decision governed by the network policies. The network policy domain
may or may not trust the end host marking. Hence, even though the network
may have supplied the DCLASS object to the end host on request (via CAP)
it may overwrite the marking based on the domain policy.
3.1 Host-Edge Router Capbility Negotiation
The advance knowledge of the end host's capabilities may help the
network edge devices to make policy decisions on end host's requests.
These capabilities can be indicated in the RSVP PATH message to the
downstream edge devices.
The end hosts can be classiffied in two categories: Those capable of
marking downstream packets and decide to do so. The other category of
hosts either do not have the capability to mark packets or they decide
not to mark packets. In either case, the network element needs to know
the host packet marking capability/willingness. This information can
help the network element to decide whether or not a DCLASS object must
be added in a RSVP message for the flow. One way to convey the host
capability/willingness to the network is to use the RSVP PATH message.
We give examples here to explain the scenarios.
If the sender host is ready to mark the downstream traffic (based on the
DCLASS provided by the network element), it sets the marking bit of the
CAP field inside the CAP object of the RSVP PATH message. On receiving
the RSVP message, the network element at the DS edge records the host
marking capability as the PATH state. It then resets the marking bit and
sends the RSVP message to the downstream nodes. The treatment of the CAP
object at the downstream nodes will be explained in next section. For now,
consider the RESV message comes back to the edge device, it performs the
necessary admission control. If the network element determines that the
request represented by the PATH and RESV messages is admissible to the
diff-serv network, it adds a DCLASS object after consulting the recorded
state. It may decide to overwrite any DCLASS object inserted by the
an downstream node/domain based on its own domain policies. This is
exactly how the DCLASS object is defined.
Another example could be the end host that is not capable of downstream
packet marking. This either will not include a CAP object or the host
will reset the marking bit of the CAP object as an indication of his
unwillingness of packet marking. The network edge router will then know
that the upstream node/end host does not require a DCLASS object. The
edge router, in this case, would be responsible for marking the downstream
packets from the end host.
Hamid Expires May, 2001 [Page 3]
draft-ietf-issll-rsvp-cap-01.txt November, 2000
3.2 Boundry router-Boundry Router Interaction
The CAP object could be carried in the PATH message end-to-end. The RSVP
PATH message is generated by the end host. The network edge router 'A'
of the DS domain processes the message, resets the marking bit of the
CAP object (if it comes as set from the host) and passes the PATH message
to the next RSVP Hop. For a DS domain, the boundray router 'B' of the
access/stub network receives the RSVP PATH message as next RSVP enabled
node (Figure 1). It may set the marking bit again to advertise the marking
capability of its own domain. The decision must be governed by the domain
policy. The ingress boundary router 'C' of the downstream domain receives
the CAP object with the marking bit set providing an indication of the
marking capability of the upstream node/domain. It again stores this
information as the PATH state, resets the marking bit and passes it to
the downstream RSVP enabled network element. The boundary router 'D' of
this domain may decide to set the marking bit again based on the domain
policy. The PATH message may pass through more domains like this until
it is received by the host. The RSVP RESV message is then generated and
passed through the same route. The RSVP message arrives at the the
router 'C' and it may contain a DCLASS object provided by an downstream
node/domain. The PATH state of router 'C' indicates that the upstream
node/domain is capable of packet marking and a DCLASS object is to be
passed back. The domain policy/admission control decisions of router 'C'
may not allow the router to use the same DCLASS value as it received
from the downstream. So it may decide to overwrite the DCLASS value. The
edge router 'A' may also decide to remark the DCLASS value in the RESV
message following its admission control outcome and knowing the end
host's willingness for packet marking. Finally, the end host receives
the DCLASS value in RESV message and it may start marking the downstream
packets with the appropriate DSCP.
Once again, It should be noted that how and when the packets will be
marked is a decision governed by the network policies. The network
policy domain may or may not trust the end host marking. Hence, even
though the network may have supplied the DCLASS object to the end host
on request (via CAP) it may overwrite the marking based on the domain
policy.
+----------+ +-----------+
|DS domain | |DS domain |
| 1 | | 2 |
+----+ +----+ +----+ +----+ +----+ +----+
|Host|-----| A | | B |----| C | | D |---''''''|Host|
+----+ +----+ +----+ +----+ +----+ +----+
| | | |
| | | |
+----------+ +-----------+
Figure 1
4. Format of CAP Object
The CAP object has the following format:
0 | 1 | 2 | 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | C-Num (226) | C-Type=1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CAP field |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Hamid Expires May, 2001 [Page 4]
draft-ietf-issll-rsvp-cap-01.txt November, 2000
CAP field:
0x01: D_MARK
The host marking capability/willingness identifier.
If D_MARK bit is reset, the sender host/upstream node
is not able to mark packets
If D_MARK bit is set, the sender host/upstream node is
able/willing to mark packets
Note: D_MARK is a bit in the CAP (capbility) field.
5. Deployment Scenarios
There are a number of hosts today which do have the marking capability
and they even do not depend on a DCLASS object from the network. The
marking is based on a default mapping from requested service type to
the DSCP. In this section, we will briefly address the deployment
scenarios for such hosts which do mark without signaling network
about their marking capability.
If a host does not provide a CAP object, then the network edge must
be provisioned (or be given policies) as to how it should react. This
may be one of:
- send a DCLASS object.
- install a filter to mark the appropriate flow at the edge.
- do both.
The problem here is ensuring that the mapping configured in the host
matches the allowed mappings configured in the edge router. If there
is a mismatch, the edge router will, at best, remark the packets to
match its policies (possibly resulting in a treatment different from
that expected by the host) or, at worst, mark packets as non-conforming
and discard them. The policy may be for a specific host address, for
a specific interface, for a specific edge router or for the entire
domain. The bottom line is that manual provisioning would be required
in the interim until hosts support the CAP option. Once hosts support
the CAP option, manual provisioning would no longer be required.
In a multi-domain scenario, the boundary router 'B' could be the first
and the only router in the first DS domain who is dealing with the
CAP/DCLASS objects (maintaining the state information and deciding for
a DSCP for the upstream end host). This will allow only one router
in a domain with the knowledge of the host's capability and will be
the one responsible for deciding/providing a DCLASS object in a RSVP
RESV message. In this scenario, the boundary router 'B' becomes the DS
edge for the end host.
6. References
[INTDIFF], Bernet, Y., Yavatkar, R., Ford, P., Baker, F., Zhang, L.,
Speer, M., Braden, R., Davie, B., Wroclawski, J., "Integrated Services
Operation over Diffserv Networks", Internet Draft, June 1999
[DS] An Architecture for Differentiated Services. S. Blake, D. Black,
M. Carlson, E. Davies, Z. Wang, W. Weiss, RFC 2475, December 1998.
Hamid Expires May, 2001 [Page 5]
draft-ietf-issll-rsvp-cap-01.txt November, 2000
[RSVP] Braden, R. ed., "Resource ReSerVation Protocol (RSVP) -
Functional Specification.", IETF RFC 2205, Sep. 1997.
[DCLASS] Bernet, Y., "Format of the RSVP DCLASS Object",
IETF <draft-ietf-isll-dclass-01.txt>, Oct., 1999.
7. Acknowledgments
Thanks to Bill Gage, Yoram Bernet, Goran Janevski, Gary Kenward,
kwok Ho chan, Muhammad Jaseemuddin and Louis-Nicolas Hamer for
reviewing this draft and providing useful input.
8. Author's Address
Syed, Hamid
Nortel Networks
100 - Constellation Crescent,
Nepean, ON K2G 6J8
Phone: (613) 763-6553
Email: hmsyed@nortelnetworks.com
9. Full Copyright Statement
"Copyright (C) The Internet Society (date). 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 organisations, 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.
Hamid Expires May, 2001 [Page 6]
draft-ietf-issll-rsvp-cap-01.txt November, 2000
