3Com 3824 Implementation Guide - Page 50

Traffic Marking, OSI Layer and Protocols, Summary of Protocols, Layer 2

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50 CHAPTER 6: USING TRAFFIC PRIORITIZATION Table 5 Attributes on which incoming traffic can be classified (identified) OSI Layer and Protocols Layer 2 ■ IEEE 802.1D priority ■ EtherType Layer 3 ■ Destination IP address ■ Source IP address ■ IP protocols: (ICMP, IGMP, RSVP, UDP, TCP, etc) ■ DiffServ code point (DSCP) Layer 4 ■ UDP / TCP Source and Destination ports for IP applications Summary of Protocols Chatty protocols such as AppleTalk and IPX, used by a small number of older devices, can cause traffic delays. Identifying and prioritizing data based on these protocols can reduce delays. AppleTalk can be identified by its EtherType of 0x809B, and IPX can be identified by EtherType 0x8137. Many applications are identified by their Source IP address, or IP protocol. Because servers are sometimes dedicated to single applications, such as email, the Source IP address or protocol in a packet can identify which application generated the packet. As well as being a traffic marking mechanism, the DSCP field in the IP header can also be used to classify traffic. Many applications use certain TCP or UDP sockets to communicate. By examining the socket number in the IP packet, the intelligent network can determine what type of application generated the packet. This is also known as Layer 4 switching. Traffic Marking After traffic has been identified through classification, it must be Marked to ensure that other devices such as Layer 2 switches or routers on the network know how to prioritize the application, device or user that generated it. The Switch uses two of the industry-standard methods of marking network traffic: ■ IEEE 802.1D - a layer 2 marking scheme. ■ Differentiated Services (DiffServ) - a layer 3 marking scheme. IEEE 802.1D Traffic Marking The IEEE Std 802.1D, 1998 Edition marking scheme is an enhancement to the IEEE Std 802.1D to enable Quality of Service in the LAN. Traffic service levels are defined in the IEEE 802.1Q 4-byte tag, which is used to carry VLAN identification as well as IEEE 802.1p priority information. The 4 byte tag immediately follows the destination MAC address and Source MAC address. The IEEE Std 802.1D, 1998 Edition priority marking scheme assigns each frame with an IEEE 802.1p priority level between 0 and 7, which

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50
C
HAPTER
6: U
SING
T
RAFFIC
P
RIORITIZATION
Table 5
Attributes on which incoming traffic can be classified (identified)
Traffic Marking
After traffic has been identified through classification, it must be Marked
to ensure that other devices such as Layer 2 switches or routers on the
network know how to prioritize the application, device or user that
generated it. The Switch uses two of the industry-standard methods of
marking network traffic:
■
IEEE 802.1D
— a layer 2 marking scheme.
■
Differentiated Services (DiffServ)
— a layer 3 marking scheme.
IEEE 802.1D Traffic Marking
The IEEE Std 802.1D, 1998 Edition marking scheme is an enhancement to
the IEEE Std 802.1D to enable Quality of Service in the LAN. Traffic service
levels are defined in the IEEE 802.1Q 4-byte tag, which is used to carry
VLAN identification as well as IEEE 802.1p priority information. The 4 byte
tag immediately follows the destination MAC address and Source MAC
address.
The IEEE Std 802.1D, 1998 Edition priority marking scheme assigns each
frame with an IEEE 802.1p priority level between 0 and 7, which
OSI Layer and Protocols
Summary of Protocols
Layer 2
■
IEEE 802.1D priority
■
EtherType
Chatty protocols such as AppleTalk and IPX, used
by a small number of older devices, can cause
traffic delays. Identifying and prioritizing data
based on these protocols can reduce delays.
AppleTalk can be identified by its EtherType of
0x809B, and IPX can be identified by EtherType
0x8137.
Layer 3
■
Destination IP address
■
Source IP address
■
IP protocols: (ICMP, IGMP,
RSVP, UDP, TCP, etc)
■
DiffServ code point (DSCP)
Many applications are identified by their Source
IP address, or IP protocol. Because servers are
sometimes dedicated to single applications, such
as email, the Source IP address or protocol in a
packet can identify which application generated
the packet.
As well as being a traffic marking mechanism,
the DSCP field in the IP header can also be used
to classify traffic.
Layer 4
■
UDP / TCP Source and
Destination ports for IP
applications
Many applications use certain TCP or UDP
sockets to communicate. By examining the
socket number in the IP packet, the intelligent
network can determine what type of application
generated the packet. This is also known as Layer
4 switching.