One document matched: draft-lee-optimal-detect-pmtu-00.txt
INTERNET-DRAFT HAK GOO LEE
Expires: March 2003 PYUNG SOO KIM
YOUNG KEUN KIM
CHU KYO SHIN
SAMSUNG ELECTRONICS
Optimal Detecting Increases in PMTU
<draft-lee-optimal-detect-pmtu-00.txt>
Status of This Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [RFC2026].
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Abstract
This document presents a new method for the detection of increases
in PMTU using the newly defined Hop-by-Hop option header.
To detect increases in a path's PMTU, a node does not increase its
assumed PMTU unconditionally without considering network status,
but measures its real PMTU, and then replaces the previous PMTU with
new one. To measure node's real PMTU, the node sends the IP packet
with the newly defined Hop-by-Hop option header to the destination
node right before a timer expires. This can eliminate the chance of
occurrence of packets being discarded and Packet Too Big messages
being generated.
Table of Contents
Abstract ............................................................1
1 Introduction.......................................................2
2 Proposed Method : Overview.........................................2
2.1 Measurement DIP Option Format................................4
2.2 Response DIP Option Format...................................4
3 Node Requirements for Proposed Method..............................5
3.1. Source Node and Destination Node............................5
3.2. Nodes on Routing Path.......................................5
4 Operation Procedure................................................6
5 References ........................................................6
6 Authors' Addresses ................................................6
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1. Introduction
Due to changes in the routing topology, the Path MTU (PMTU) of a
path may change over time. Therefore, in Path MTU Discovery
[RFC1981], to detect increases in a path's PMTU, a node
periodically increases its assumed PMTU although this is done
infrequently. However, in this method, the assumed PMTU is
increased by the node's link MTU unconditionally. This may
result in packets being discarded and Packet Too Big messages
being generated.
Therefore, this document presents a new method for the detection of
increases in PMTU using the newly defined Hop-by-Hop Option header.
In this new method, to detect increases in a path's PMTU, a node
does not increase its assumed PMTU unconditionally without
considering network status, but measures its real PMTU, and then
replaces the previous PMTU with new one.
To measure node's real PMTU, the node sends the IP packet with the
newly defined Hop-by-Hop option header to the destination node
right before a timer expires. In this document, this timer will be
called the detection timer. The recommended setting for this
detection timer is also 10 minutes as [RFC1981].
Note that the newly obtained PMTU is always greater than or equal
to the previous one. After then, the new PMTU is used to send
packets. This can eliminate the chance of occurrence of packets
being discarded and Packet Too Big messages being generated, which
might occur when the assumed PMTU is increased unconditionally by
the detection timer in PMTU Discovery [RFC1981].
The proposed method in this document can provide the best-conditioned
network environment because the optimized PMTU is obtained for
changes in the routing topology.
2. Proposed Method : Overview
This section gives a brief overview of the new method for the
detection of increases in PMTU.
A router on routing path examines only IP header, Hop-by-Hop option
header and routing header in extension header. Other extension
headers and data are examined only by a source node and destination
node. In the new method, Hop-by-Hop option header is used to
measure increases in a path's PMTU
The Hop-by-Hop option header and option is defined as below.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
. .
. Options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1 Hop-by-Hop Option Header
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Currently, Hop-by-Hop option headers are Pad1, PadN, Jumbo Payload,
and Router Alert options. This document defines a new option. It is
called 'Detection of Increasing PMTU option (DIP option)'.
Then, the IP packet including Hop-by-Hop option header with DIP
option has the following format.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| Traffic Class | Flow Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Length | Next Header | Hop Limint |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Source Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Destination Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | 0 | Option Type | Opt Data Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Data(PMTU) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Dummy Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
| ....
+-+
Option Type 8-bit identifier of the type of option.
Opt Data Len 8-bit unsigned integer. Length of the Option
Data field of this option, in octets.
Option Data(PMTU) Measured PMTU value with 4 bytes
Figure 2 IP Packet with DIP option
The Option Type identifiers are internally encoded such that their
highest-order two bits specify the action that must be taken when
the router does not recognize the Option Type. The third highest
order bit of the Option Type specifies whether or not the Option
Data (PMTU) of that option can change en-route to the packet's
final destination. The other five bits are defined arbitrarily.
The DIP option has two Option Types. The one is Measurement DIP
Option and the other is Response DIP Option, which will be shown
in following subsections. If any of the routers en-route cannot
recognize the Option Types, it discards the packet silently.
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2.1 Measurement DIP Option Format
The measurement DIP option format is defined to measure real
PMTU as shown in Figure 2. The source node sends the IP packet
with this measurement DIP option format to the destination node.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 1 1|0 0 1 1 1|0 0 0 0 0 1 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| P M T U |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
01 - Discard the packet
1 - Option Data may change en-route
00111 - Option Type
Option Type - 103
Option Length - 4
PMTU - 4 Octets
Figure 3 Measurement DIP Option Format
2.2 Response DIP Option Format
The response DIP option format is defined to response measured
real PMTU as shown in Figure 3. The destination node sends the IP
packet with this response DIP option format to the source node.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 1 0|0 0 1 1 1|0 0 0 0 0 1 0 0|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| P M T U |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
01 - Discard the packet
0 - Option Data does not change en-route
00111 - Option Type
Option Type - 71
Option Length - 4
PMTU - 4 Octets
Figure 4 Measurement DIP Option Format
As described on Path MTU Discovery [RFC 1981], a source node sends
IP packet with Measurement DIP Option to a destination node before
the detection timer expires so that it wants to increase PMTU
value. Default MTU value is link MTU of the source node. While the
packet is passing through nodes en-route, the following action
occurs.
- Compare PMTU in Measurement DIP Option and Link MTU of next hop.
- Store the smaller value between them on MTU field of the packet.
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By doing the same action on routers en-route, PMTU field of the IP
packet with Measurement DIP Option is updated to have minimum PMTU.
This is the optimal PMTU value. The destination node that
receives the IP packet returns back this value to the source node
using Response DIP Option. The source node that receives the
optimal PMTU value determines the transmission length of a packet.
This method can reduce the number of ICMP-Packet Too Big Error
message, otherwise happens more frequently. This also reduce waste
of network resource
3. Node Requirements for Proposed Method
3.1. Source Node and Destination Node
A source node does not change the PMTU value for some amount of
time after it comes to know PMTU based on PMTU Discovery [RFC1981].
When the source node wants to increase PMTU by the detection timer,
it sends the IP packet with Measurement DIP Option to a
destination. The PMTU field of Measurement DIP Option of the packet
contains the value of link MTU of the source node and the data
field contains dummy data. If the packet is discarded by a router
that does not understand the packet format on routing, no response
returns to the source node. For this reason, the source node uses
a timer while transmitting the packet. This timer will be called
the response timer. If there is no response until the response timer
expires, the source node increase the PMTU as described in Path MTU
Discovery [RFC1981].
Whenever a destination node receives the IP packet with Measurement
DIP Option, it must response the IP packet with Response DIP Option
immediately. By the Option Type, this packet cannot be modified by
routers on routing path.
3.2. Nodes on Routing Path
Nodes on a routing path are routers. When the IP packet with
Measurement DIP Option arrives on these routers, they compare the
PMTU in Measurement DIP Option and link MTU of the next hop. They
select a smaller value between them and forward the packet with
a PMTU value. After doing the same procedure, the final
destination node comes to know minimum PMTU. If the IP packet with
Response DIP Option arrives on theses routers, they forward the
packet without any modification. If routers can not recognize two
DIP Options, it discard the packet silently without any error
message such as ICMP-Parameter Problem since the first two bits of
the DIP Option is 01.
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4. Operation Procedure
When the source node wants to increase PMTU by the detection timer,
it sends the IP packet with Measurement DIP Option to a destination.
In this case, the Option Type in Measurement DIP Option is 103.
While the packet is en-route, intermediate routers compare the PMTU
in Measurement DIP Option and link MTU of the next hop. They select
a smaller value between them, store the value to PMTU field of
Measurement DIP Option and forward the packet with the updated PMTU.
PMTU of the packet arrived at the destination node becomes minimum
PMTU. The destination node sends the IP packet Response DIP Option
to inform the source node. In this case, the Option Type in
Measurement DIP Option is 71. After then, the source node sends
packets using new PMTU. If there are routers that this feature
is not implemented during transitional period, that is, if routers
implements only previous PMTU Discovery [RFC 1981] on
routing path, the DIP Options defined newly in this document is
unknown parameter. Thus, in this case the router can silently
discard the packet without ICMP-Parameter problem by the
highest-order two bits, 01, in Option Type field. Additionally, the
source node operates the response timer when transmitting the packet
with DIP option. If the source node does not receive the IP packet
with Response DIP Option until the response timer expires, the
source node increase PMTU as described in Path MTU Discovery
[RFC1981].
5 References
[RFC1981] Path MTU Discovery for IP version 6 (RFC 1981)
6 Authors' Addresses
HAK GOO LEE
Digital Media R&D Center, SAMSUNG ELECTRONICS
Tel : +82 31 200 9309
Fax : +82 31 200 3147
E-mail : solited@samsung.co.kr
PYUNG SOO KIM
Digital Media R&D Center, SAMSUNG ELECTRONICS
Tel : +82 31 200 4635
Fax : +82 31 200 3147
E-mail : kimps@samsung.com
YOUNG KEUN KIM
Digital Media R&D Center, SAMSUNG ELECTRONICS
Tel : +82 31 200 3772
Fax : +82 31 200 3147
E-mail : ykksam@samsung.com
CHU KYO SHIN
Digital Media R&D Center, SAMSUNG ELECTRONICS
Tel : +82 31 200 8318
Fax : +82 31 200 3147
E-mail : kyoshin@samsung.com
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