Comments for Darrell Stephenson

Comment on Post LASIK Thoughts by C

Fri, 25 Apr 2008 09:15:34 +0000

PowerConnect Application Note #18 February 2004
http://www.dell.com/networking 1
Understanding IGMP Snooping
This Application Note relates to the following Dell PowerConnect�?� product(s):
�?� PowerConnect 33xx switches
Abstract
This Application Note explains how a feature called IGMP snooping can significantly reduce traffic from
streaming media and other bandwidth-intensive IP multicast applications. This document introduces the
IGMP protocol and provides step-by-step instructions for configuring Dell PowerConnect 33xx switches to
use IGMP snooping.
Applicable Network Scenarios
By default, layer 2 devices such as Dell PowerConnect 33xx switches treat IP multicast traffic in the same
manner as broadcast traffic �?? namely, by forwarding frames received on one interface to all other
interfaces. This may create excessive traffic on the network and degrade the performance of hosts
attached to the switches. Every frame received by each host generates an interrupt that the host must
process, robbing cycles that might instead be used by applications.
Layer 3 devices have less of a problem with rampant broadcast and multicast traffic because of their
ability to segment networks and forward traffic only to actual destination interfaces.
With Internet Group Management Protocol (IGMP) snooping, Layer 2 devices also can make intelligent
multicast forwarding decisions by examining the contents of each frame�??s Layer 3 IP header.
Consider the example of a heterogeneous Layer 2 and Layer 3 network that does not use IGMP snooping.
The figure below shows a simple network in which eight hosts connect to four Layer 2 switches. The
switches in turn connect to one router in the middle.
A
B
C
D
PowerConnect Application Note #18: Understanding IGMP Snooping
http://www.dell.com/networking 2
Now suppose Host A is an IP multicast transmitter and Hosts B and C are multicast receivers in the same
group as Host A. The router will correctly forward IP multicast traffic only to those segments with
registered receivers (Hosts B and C). However, the Layer 2 switches will flood the traffic to all hosts on all
interfaces.
A
B
C
D
The larger the network grows, the greater the performance impact of this extraneous multicast traffic.
Now we can see what happens with the addition of IGMP Snooping on the Layer 2 devices. Just as
desired, only hosts that are group receivers actually receive multicast traffic.
A
B
C
D
Technology Background
The Internet Engineering Task Force (IETF) defined IGMP as a means of associating groups of IP
multicast transmitters and receivers. Each member host of an IP multicast is either a transmitter or a
receiver.
A station that wishes to become a receiver sends an IGMP �??group join�?? message to that group�??s
transmitter. Each Layer 3 device that forwards an IGMP join message records the group ID and source
PowerConnect Application Note #18: Understanding IGMP Snooping
http://www.dell.com/networking 3
interface in its multicast forwarding table. When the transmitter sends IP multicast traffic, the Layer 3
device will then forward the traffic only to those interfaces from which it has received join messages.
Thus, the Layer 3 device forwards IP multicast traffic only to those hosts that have requested it.
Applications that use IP multicast, such as those involving streaming media, automatically handle IP
multicast group membership. Users do not have to manually send IGMP messages.
Over time, the IETF has defined three versions of IGMP:
IGMPv1: IETF Request for Comments 1112 (RFC 1112) defines the original version of IGMP. RFC 1112
defines the join message that hosts use to join an IP multicast group. However, IGMPv1 does not define
a method for hosts to leave a multicast group. With IGMPv1, routers must use a timer to determine which
hosts are still members of the group.
IGMPv2: RFC 2236 defines �??group leave�?? messages that enable IP multicast-aware devices to keep
current information on group membership.
IGMPv3: RFC 3376 represents a major revision of IGMP. Instead of the one-transmitter/many-receiver
model of IGMP versions 1 and 2, hosts using IGMPv3 specify lists of transmitters to listen to.
IGMP snooping, as the name implies, is a method by which Layer 2 devices can �??listen in�?? on IGMP
conversations between hosts and routers. When a switch hears a group join message from a host, it
notes which switch interface it heard the message on, and adds that interface to the group. Similarly,
when a Layer 2 switch hears a group leave message or a response timer expires, the switch will remove
that host�??s switch interface from the group.
IP multicast traffic has some special characteristics. Destination IP addresses for multicast traffic fall
within the range of 224.0.0.1 through 239.255.255.255 (although some addresses within this range are
reserved). Destination Ethernet addresses for multicast traffic begin with 01:00:5E and end with the loworder
23 bits of the destination IP address.
Proposed Solution
Overview
Configuring IGMP snooping is a simple two-step process on Dell PowerConnect 33xx switches. First you
must enable IGMP snooping, and then you enable filtering of multicast traffic. Two examples are given
here:
�?� Enabling IGMP snooping globally for all interfaces on a Dell PowerConnect 3348 switch
�?� Enabling IGMP snooping for interfaces of a selected VLAN on a Dell PowerConnect 3348 switch
While it is possible to restrict the scope of IGMP snooping by enabling it only on selected VLANs, it is a
much more common practice to enable IGMP snooping on all switch interfaces.
Note that at least one Layer 3 device must exist in the network for IP multicast and IGMP snooping to
work. Layer 2 switches by themselves cannot support IP multicast service.
Step-By-Step Instructions
1. To enable IGMP snooping for all switch interfaces, enter the following commands from the console:
Dell-3348> enable
Dell-3348# configure
Dell-3348(config)# ip igmp snooping
Dell-3348(config)# bridge multicast filtering
PowerConnect Application Note #18: Understanding IGMP Snooping
http://www.dell.com/networking 4
Dell-3348(config)# end
Dell-3348# copy running-config startup-config
This sequence puts the switch in executive mode; enters into configuration mode; enables IGMP
snooping globally; enables selective forwarding of multicast traffic; exits configuration mode; and saves
the running configuration.
2. To enable IGMP snooping for a given VLAN (we use VLAN ID 100 in this example), enter the following
commands from the console:
Dell-3348> enable
Dell-3348# configure
Dell-3348(config)# int vlan 100
Dell-3348(config-if)# ip igmp snooping
Dell-3348(config-if)# bridge multicast filtering
Dell-3348(config-if)# end
Dell-3348# copy running-config startup-config
This sequence puts the switch in executive mode; enters into configuration mode; selects VLAN 100 for
configuration; enables IGMP snooping on VLAN 100; enables selective forwarding of multicast traffic;
exits configuration mode; and saves the running configuration.
Conclusion
As described above, IGMP snooping can provide a simple yet effective means of reducing unwanted
traffic from the network. With IGMP snooping enabled globally, a Dell PowerConnect switch will forward
IP multicast traffic only to interfaces with group members attached.
This Application Note is for informational purposes only, and may contain typographical errors and technical inaccuracies. The
content is provided as is, without express or implied warranties of any kind.
disclaims any proprietary interest in trademarks and trade names other than its own. © 2004 Dell Inc. All rights reserved.

Comment on Post LASIK Thoughts by CC

CC — Fri, 25 Apr 2008 09:15:12 +0000

PowerConnect Application Note #18 February 2004
http://www.dell.com/networking 1
Understanding IGMP Snooping
This Application Note relates to the following Dell PowerConnect�?� product(s):
�?� PowerConnect 33xx switches
Abstract
This Application Note explains how a feature called IGMP snooping can significantly reduce traffic from
streaming media and other bandwidth-intensive IP multicast applications. This document introduces the
IGMP protocol and provides step-by-step instructions for configuring Dell PowerConnect 33xx switches to
use IGMP snooping.
Applicable Network Scenarios
By default, layer 2 devices such as Dell PowerConnect 33xx switches treat IP multicast traffic in the same
manner as broadcast traffic �?? namely, by forwarding frames received on one interface to all other
interfaces. This may create excessive traffic on the network and degrade the performance of hosts
attached to the switches. Every frame received by each host generates an interrupt that the host must
process, robbing cycles that might instead be used by applications.
Layer 3 devices have less of a problem with rampant broadcast and multicast traffic because of their
ability to segment networks and forward traffic only to actual destination interfaces.
With Internet Group Management Protocol (IGMP) snooping, Layer 2 devices also can make intelligent
multicast forwarding decisions by examining the contents of each frame�??s Layer 3 IP header.
Consider the example of a heterogeneous Layer 2 and Layer 3 network that does not use IGMP snooping.
The figure below shows a simple network in which eight hosts connect to four Layer 2 switches. The
switches in turn connect to one router in the middle.
A
B
C
D
PowerConnect Application Note #18: Understanding IGMP Snooping
http://www.dell.com/networking 2
Now suppose Host A is an IP multicast transmitter and Hosts B and C are multicast receivers in the same
group as Host A. The router will correctly forward IP multicast traffic only to those segments with
registered receivers (Hosts B and C). However, the Layer 2 switches will flood the traffic to all hosts on all
interfaces.
A
B
C
D
The larger the network grows, the greater the performance impact of this extraneous multicast traffic.
Now we can see what happens with the addition of IGMP Snooping on the Layer 2 devices. Just as
desired, only hosts that are group receivers actually receive multicast traffic.
A
B
C
D
Technology Background
The Internet Engineering Task Force (IETF) defined IGMP as a means of associating groups of IP
multicast transmitters and receivers. Each member host of an IP multicast is either a transmitter or a
receiver.
A station that wishes to become a receiver sends an IGMP �??group join�?? message to that group�??s
transmitter. Each Layer 3 device that forwards an IGMP join message records the group ID and source
PowerConnect Application Note #18: Understanding IGMP Snooping
http://www.dell.com/networking 3
interface in its multicast forwarding table. When the transmitter sends IP multicast traffic, the Layer 3
device will then forward the traffic only to those interfaces from which it has received join messages.
Thus, the Layer 3 device forwards IP multicast traffic only to those hosts that have requested it.
Applications that use IP multicast, such as those involving streaming media, automatically handle IP
multicast group membership. Users do not have to manually send IGMP messages.
Over time, the IETF has defined three versions of IGMP:
IGMPv1: IETF Request for Comments 1112 (RFC 1112) defines the original version of IGMP. RFC 1112
defines the join message that hosts use to join an IP multicast group. However, IGMPv1 does not define
a method for hosts to leave a multicast group. With IGMPv1, routers must use a timer to determine which
hosts are still members of the group.
IGMPv2: RFC 2236 defines �??group leave�?? messages that enable IP multicast-aware devices to keep
current information on group membership.
IGMPv3: RFC 3376 represents a major revision of IGMP. Instead of the one-transmitter/many-receiver
model of IGMP versions 1 and 2, hosts using IGMPv3 specify lists of transmitters to listen to.
IGMP snooping, as the name implies, is a method by which Layer 2 devices can �??listen in�?? on IGMP
conversations between hosts and routers. When a switch hears a group join message from a host, it
notes which switch interface it heard the message on, and adds that interface to the group. Similarly,
when a Layer 2 switch hears a group leave message or a response timer expires, the switch will remove
that host�??s switch interface from the group.
IP multicast traffic has some special characteristics. Destination IP addresses for multicast traffic fall
within the range of 224.0.0.1 through 239.255.255.255 (although some addresses within this range are
reserved). Destination Ethernet addresses for multicast traffic begin with 01:00:5E and end with the loworder
23 bits of the destination IP address.
Proposed Solution
Overview
Configuring IGMP snooping is a simple two-step process on Dell PowerConnect 33xx switches. First you
must enable IGMP snooping, and then you enable filtering of multicast traffic. Two examples are given
here:
�?� Enabling IGMP snooping globally for all interfaces on a Dell PowerConnect 3348 switch
�?� Enabling IGMP snooping for interfaces of a selected VLAN on a Dell PowerConnect 3348 switch
While it is possible to restrict the scope of IGMP snooping by enabling it only on selected VLANs, it is a
much more common practice to enable IGMP snooping on all switch interfaces.
Note that at least one Layer 3 device must exist in the network for IP multicast and IGMP snooping to
work. Layer 2 switches by themselves cannot support IP multicast service.
Step-By-Step Instructions
1. To enable IGMP snooping for all switch interfaces, enter the following commands from the console:
Dell-3348> enable
Dell-3348# configure
Dell-3348(config)# ip igmp snooping
Dell-3348(config)# bridge multicast filtering
PowerConnect Application Note #18: Understanding IGMP Snooping
http://www.dell.com/networking 4
Dell-3348(config)# end
Dell-3348# copy running-config startup-config
This sequence puts the switch in executive mode; enters into configuration mode; enables IGMP
snooping globally; enables selective forwarding of multicast traffic; exits configuration mode; and saves
the running configuration.
2. To enable IGMP snooping for a given VLAN (we use VLAN ID 100 in this example), enter the following
commands from the console:
Dell-3348> enable
Dell-3348# configure
Dell-3348(config)# int vlan 100
Dell-3348(config-if)# ip igmp snooping
Dell-3348(config-if)# bridge multicast filtering
Dell-3348(config-if)# end
Dell-3348# copy running-config startup-config
This sequence puts the switch in executive mode; enters into configuration mode; selects VLAN 100 for
configuration; enables IGMP snooping on VLAN 100; enables selective forwarding of multicast traffic;
exits configuration mode; and saves the running configuration.
Conclusion
As described above, IGMP snooping can provide a simple yet effective means of reducing unwanted
traffic from the network. With IGMP snooping enabled globally, a Dell PowerConnect switch will forward
IP multicast traffic only to interfaces with group members attached.
This Application Note is for informational Dell Inc. Other trademarks and trade
names may be used in this document to refer to either the entities claiming the marks and names or their products. Dell Inc.
disclaims any proprietary interest in trademarks and trade names other than its own. © 2004 Dell Inc. All rights reserved.

Comment on Post LASIK Thoughts by N

Fri, 25 Apr 2008 09:14:40 +0000

PowerConnect Application Note #18 February 2004
http://www.dell.com/networking 1
Understanding IGMP Snooping
This Application Note relates to the following Dell PowerConnect�?� product(s):
�?� PowerConnect 33xx switches
Abstract
This Application Note explains how a feature called IGMP snooping can significantly reduce traffic from
streaming media and other bandwidth-intensive IP multicast applications. This document introduces the
IGMP protocol and provides step-by-step instructions for configuring Dell PowerConnect 33xx switches to
use IGMP snooping.
Applicable Network Scenarios
By default, layer 2 devices such as Dell PowerConnect 33xx switches treat IP multicast traffic in the same
manner as broadcast traffic �?? namely, by forwarding frames received on one interface to all other
interfaces. This may create excessive traffic on the network and degrade the performance of hosts
attached to the switches. Every frame received by each host generates an interrupt that the host must
process, robbing cycles that might instead be used by applications.
Layer 3 devices have less of a problem with rampant broadcast and multicast traffic because of their
ability to segment networks and forward traffic only to actual destination interfaces.
With Internet Group Management Protocol (IGMP) snooping, Layer 2 devices also can make intelligent
multicast forwarding decisions by examining the contents of each frame�??s Layer 3 IP header.
Consider the example of a heterogeneous Layer 2 and Layer 3 network that does not use IGMP snooping.
The figure below shows a simple network in which eight hosts connect to four Layer 2 switches. The
switches in turn connect to one router in the middle.
A
B
C
D
PowerConnect Application Note #18: Understanding IGMP Snooping
http://www.dell.com/networking 2
Now suppose Host A is an IP multicast transmitter and Hosts B and C are multicast receivers in the same
group as Host A. The router will correctly forward IP multicast traffic only to those segments with
registered receivers (Hosts B and C). However, the Layer 2 switches will flood the traffic to all hosts on all
interfaces.
A
B
C
D
The larger the network grows, the greater the performance impact of this extraneous multicast traffic.
Now we can see what happens with the addition of IGMP Snooping on the Layer 2 devices. Just as
desired, only hosts that are group receivers actually receive multicast traffic.
A
B
C
D
Technology Background
The Internet Engineering Task Force (IETF) defined IGMP as a means of associating groups of IP
multicast transmitters and receivers. Each member host of an IP multicast is either a transmitter or a
receiver.
A station that wishes to become a receiver sends an IGMP �??group join�?? message to that group�??s
transmitter. Each Layer 3 device that forwards an IGMP join message records the group ID and source
PowerConnect Application Note #18: Understanding IGMP Snooping
http://www.dell.com/networking 3
interface in its multicast forwarding table. When the transmitter sends IP multicast traffic, the Layer 3
device will then forward the traffic only to those interfaces from which it has received join messages.
Thus, the Layer 3 device forwards IP multicast traffic only to those hosts that have requested it.
Applications that use IP multicast, such as those involving streaming media, automatically handle IP
multicast group membership. Users do not have to manually send IGMP messages.
Over time, the IETF has defined three versions of IGMP:
IGMPv1: IETF Request for Comments 1112 (RFC 1112) defines the original version of IGMP. RFC 1112
defines the join message that hosts use to join an IP multicast group. However, IGMPv1 does not define
a method for hosts to leave a multicast group. With IGMPv1, routers must use a timer to determine which
hosts are still members of the group.
IGMPv2: RFC 2236 defines �??group leave�?? messages that enable IP multicast-aware devices to keep
current information on group membership.
IGMPv3: RFC 3376 represents a major revision of IGMP. Instead of the one-transmitter/many-receiver
model of IGMP versions 1 and 2, hosts using IGMPv3 specify lists of transmitters to listen to.
IGMP snooping, as the name implies, is a method by which Layer 2 devices can �??listen in�?? on IGMP
conversations between hosts and routers. When a switch hears a group join message from a host, it
notes which switch interface it heard the message on, and adds that interface to the group. Similarly,
when a Layer 2 switch hears a group leave message or a response timer expires, the switch will remove
that host�??s switch interface from the group.
IP multicast traffic has some special characteristics. Destination IP addresses for multicast traffic fall
within the range of 224.0.0.1 through 239.255.255.255 (although some addresses within this range are
reserved). Destination Ethernet addresses for multicast traffic begin with 01:00:5E and end with the loworder
23 bits of the destination IP address.
Proposed Solution
Overview
Configuring IGMP snooping is a simple two-step process on Dell PowerConnect 33xx switches. First you
must enable IGMP snooping, and then you enable filtering of multicast traffic. Two examples are given
here:
�?� Enabling IGMP snooping globally for all interfaces on a Dell PowerConnect 3348 switch
�?� Enabling IGMP snooping for interfaces of a selected VLAN on a Dell PowerConnect 3348 switch
While it is possible to restrict the scope of IGMP snooping by enabling it only on selected VLANs, it is a
much more common practice to enable IGMP snooping on all switch interfaces.
Note that at least one Layer 3 device must exist in the network for IP multicast and IGMP snooping to
work. Layer 2 switches by themselves cannot support IP multicast service.
Step-By-Step Instructions
1. To enable IGMP snooping for all switch interfaces, enter the following commands from the console:
Dell-3348> enable
Dell-3348# configure
Dell-3348(config)# ip igmp snooping
Dell-3348(config)# bridge multicast filtering
PowerConnect Application Note #18: Understanding IGMP Snooping
http://www.dell.com/networking 4
Dell-3348(config)# end
Dell-3348# copy running-config startup-config
This sequence puts the switch in executive mode; enters into configuration mode; enables IGMP
snooping globally; enables selective forwarding of multicast traffic; exits configuration mode; and saves
the running configuration.
2. To enable IGMP snooping for a given VLAN (we use VLAN ID 100 in this example), enter the following
commands from the console:
Dell-3348> enable
Dell-3348# configure
Dell-3348(config)# int vlan 100
Dell-3348(config-if)# ip igmp snooping
Dell-3348(config-if)# bridge multicast filtering
Dell-3348(config-if)# end
Dell-3348# copy running-config startup-config
This sequence puts the switch in executive mode; enters into configuration mode; selects VLAN 100 for
configuration; enables IGMP snooping on VLAN 100; enables selective forwarding of multicast traffic;
exits configuration mode; and saves the running configuration.
Conclusion
As described above, IGMP snooping can provide a simple yet effective means of reducing unwanted
traffic from the network. With IGMP snooping enabled globally, a Dell PowerConnect switch will forward
IP multicast traffic only to interfaces with group members attached.
This Application Note is for informational purposes only, and may contain typographical errors and technical inaccuracies. The
content is provided as is, without express or implied warranties of any kind. Information in this document is subject to change
without notice.
Trademarks used in this text: Dell, the DELL

Comment on Post LASIK Thoughts by UU

UU — Fri, 25 Apr 2008 09:14:20 +0000

PowerConnect Application Note #18 February 2004
http://www.dell.com/networking 1
Understanding IGMP Snooping
This Application Note relates to the following Dell PowerConnect�?� product(s):
�?� PowerConnect 33xx switches
Abstract
This Application Note explains how a feature called IGMP snooping can significantly reduce traffic from
streaming media and other bandwidth-intensive IP multicast applications. This document introduces the
IGMP protocol and provides step-by-step instructions for configuring Dell PowerConnect 33xx switches to
use IGMP snooping.
Applicable Network Scenarios
By default, layer 2 devices such as Dell PowerConnect 33xx switches treat IP multicast traffic in the same
manner as broadcast traffic �?? namely, by forwarding frames received on one interface to all other
interfaces. This may create excessive traffic on the network and degrade the performance of hosts
attached to the switches. Every frame received by each host generates an interrupt that the host must
process, robbing cycles that might instead be used by applications.
Layer 3 devices have less of a problem with rampant broadcast and multicast traffic because of their
ability to segment networks and forward traffic only to actual destination interfaces.
With Internet Group Management Protocol (IGMP) snooping, Layer 2 devices also can make intelligent
multicast forwarding decisions by examining the contents of each frame�??s Layer 3 IP header.
Consider the example of a heterogeneous Layer 2 and Layer 3 network that does not use IGMP snooping.
The figure below shows a simple network in which eight hosts connect to four Layer 2 switches. The
switches in turn connect to one router in the middle.
A
B
C
D
PowerConnect Application Note #18: Understanding IGMP Snooping
http://www.dell.com/networking 2
Now suppose Host A is an IP multicast transmitter and Hosts B and C are multicast receivers in the same
group as Host A. The router will correctly forward IP multicast traffic only to those segments with
registered receivers (Hosts B and C). However, the Layer 2 switches will flood the traffic to all hosts on all
interfaces.
A
B
C
D
The larger the network grows, the greater the performance impact of this extraneous multicast traffic.
Now we can see what happens with the addition of IGMP Snooping on the Layer 2 devices. Just as
desired, only hosts that are group receivers actually receive multicast traffic.
A
B
C
D
Technology Background
The Internet Engineering Task Force (IETF) defined IGMP as a means of associating groups of IP
multicast transmitters and receivers. Each member host of an IP multicast is either a transmitter or a
receiver.
A station that wishes to become a receiver sends an IGMP �??group join�?? message to that group�??s
transmitter. Each Layer 3 device that forwards an IGMP join message records the group ID and source
PowerConnect Application Note #18: Understanding IGMP Snooping
http://www.dell.com/networking 3
interface in its multicast forwarding table. When the transmitter sends IP multicast traffic, the Layer 3
device will then forward the traffic only to those interfaces from which it has received join messages.
Thus, the Layer 3 device forwards IP multicast traffic only to those hosts that have requested it.
Applications that use IP multicast, such as those involving streaming media, automatically handle IP
multicast group membership. Users do not have to manually send IGMP messages.
Over time, the IETF has defined three versions of IGMP:
IGMPv1: IETF Request for Comments 1112 (RFC 1112) defines the original version of IGMP. RFC 1112
defines the join message that hosts use to join an IP multicast group. However, IGMPv1 does not define
a method for hosts to leave a multicast group. With IGMPv1, routers must use a timer to determine which
hosts are still members of the group.
IGMPv2: RFC 2236 defines �??group leave�?? messages that enable IP multicast-aware devices to keep
current information on group membership.
IGMPv3: RFC 3376 represents a major revision of IGMP. Instead of the one-transmitter/many-receiver
model of IGMP versions 1 and 2, hosts using IGMPv3 specify lists of transmitters to listen to.
IGMP snooping, as the name implies, is a method by which Layer 2 devices can �??listen in�?? on IGMP
conversations between hosts and routers. When a switch hears a group join message from a host, it
notes which switch interface it heard the message on, and adds that interface to the group. Similarly,
when a Layer 2 switch hears a group leave message or a response timer expires, the switch will remove
that host�??s switch interface from the group.
IP multicast traffic has some special characteristics. Destination IP addresses for multicast traffic fall
within the range of 224.0.0.1 through 239.255.255.255 (although some addresses within this range are
reserved). Destination Ethernet addresses for multicast traffic begin with 01:00:5E and end with the loworder
23 bits of the destination IP address.
Proposed Solution
Overview
Configuring IGMP snooping is a simple two-step process on Dell PowerConnect 33xx switches. First you
must enable IGMP snooping, and then you enable filtering of multicast traffic. Two examples are given
here:
�?� Enabling IGMP snooping globally for all interfaces on a Dell PowerConnect 3348 switch
�?� Enabling IGMP snooping for interfaces of a selected VLAN on a Dell PowerConnect 3348 switch
While it is possible to restrict the scope of IGMP snooping by enabling it only on selected VLANs, it is a
much more common practice to enable IGMP snooping on all switch interfaces.
Note that at least one Layer 3 device must exist in the network for IP multicast and IGMP snooping to
work. Layer 2 switches by themselves cannot support IP multicast service.
Step-By-Step Instructions
1. To enable IGMP snooping for all switch interfaces, enter the following commands from the console:
Dell-3348> enable
Dell-3348# configure
Dell-3348(config)# ip igmp snooping
Dell-3348(config)# bridge multicast filtering
PowerConnect Application Note #18: Understanding IGMP Snooping
http://www.dell.com/networking 4
Dell-3348(config)# end
Dell-3348# copy running-config startup-config
This sequence puts the switch in executive mode; enters into configuration mode; enables IGMP
snooping globally; enables selective forwarding of multicast traffic; exits configuration mode; and saves
the running configuration.
2. To enable IGMP snooping for a given VLAN (we use VLAN ID 100 in this example), enter the following
commands from the console:
Dell-3348> enable
Dell-3348# configure
Dell-3348(config)# int vlan 100
Dell-3348(config-if)# ip igmp snooping
Dell-3348(config-if)# bridge multicast filtering
Dell-3348(config-if)# end
Dell-3348# copy running-config startup-config
This sequence puts the switch in executive mode; enters into configuration mode; selects VLAN 100 for
configuration; enables IGMP snooping on VLAN 100; enables selective forwarding of multicast traffic;
exits configuration mode; and saves the running configuration.
Conclusion
As described above, IGMP snooping can provide a simple yet effective means of reducing unwanted
traffic from the network. With IGMP snooping enabled globally, a Dell PowerConnect switch will forward
IP multicast traffic only to interfaces with group members attached.
This Application Note is for informational purposes only, and may contain typographical errors and technical inaccuracies. The
content is provided as is, without express or implied warranties of any kind. Information in this document is subject to change
without notice.
Trademarks used in this text: Dell, the DELL logo, and PowerConnect are trademarks of Dell Inc. Other trademarks and trade
names may be used in this document to refer to either own. © 2004 Dell Inc. All rights reserved.

Comment on Post LASIK Thoughts by gg

gg — Fri, 25 Apr 2008 09:14:01 +0000

PowerConnect Application Note #18 February 2004
http://www.dell.com/networking 1
Understanding IGMP Snooping
This Application Note relates to the following Dell PowerConnect�?� product(s):
�?� PowerConnect 33xx switches
Abstract
This Application Note explains how a feature called IGMP snooping can significantly reduce traffic from
streaming media and other bandwidth-intensive IP multicast applications. This document introduces the
IGMP protocol and provides step-by-step instructions for configuring Dell PowerConnect 33xx switches to
use IGMP snooping.
Applicable Network Scenarios
By default, layer 2 devices such as Dell PowerConnect 33xx switches treat IP multicast traffic in the same
manner as broadcast traffic �?? namely, by forwarding frames received on one interface to all other
interfaces. This may create excessive traffic on the network and degrade the performance of hosts
attached to the switches. Every frame received by each host generates an interrupt that the host must
process, robbing cycles that might instead be used by applications.
Layer 3 devices have less of a problem with rampant broadcast and multicast traffic because of their
ability to segment networks and forward traffic only to actual destination interfaces.
With Internet Group Management Protocol (IGMP) snooping, Layer 2 devices also can make intelligent
multicast forwarding decisions by examining the contents of each frame�??s Layer 3 IP header.
Consider the example of a heterogeneous Layer 2 and Layer 3 network that does not use IGMP snooping.
The figure below shows a simple network in which eight hosts connect to four Layer 2 switches. The
switches in turn connect to one router in the middle.
A
B
C
D
PowerConnect Application Note #18: Understanding IGMP Snooping
http://www.dell.com/networking 2
Now suppose Host A is an IP multicast transmitter and Hosts B and C are multicast receivers in the same
group as Host A. The router will correctly forward IP multicast traffic only to those segments with
registered receivers (Hosts B and C). However, the Layer 2 switches will flood the traffic to all hosts on all
interfaces.
A
B
C
D
The larger the network grows, the greater the performance impact of this extraneous multicast traffic.
Now we can see what happens with the addition of IGMP Snooping on the Layer 2 devices. Just as
desired, only hosts that are group receivers actually receive multicast traffic.
A
B
C
D
Technology Background
The Internet Engineering Task Force (IETF) defined IGMP as a means of associating groups of IP
multicast transmitters and receivers. Each member host of an IP multicast is either a transmitter or a
receiver.
A station that wishes to become a receiver sends an IGMP �??group join�?? message to that group�??s
transmitter. Each Layer 3 device that forwards an IGMP join message records the group ID and source
PowerConnect Application Note #18: Understanding IGMP Snooping
http://www.dell.com/networking 3
interface in its multicast forwarding table. When the transmitter sends IP multicast traffic, the Layer 3
device will then forward the traffic only to those interfaces from which it has received join messages.
Thus, the Layer 3 device forwards IP multicast traffic only to those hosts that have requested it.
Applications that use IP multicast, such as those involving streaming media, automatically handle IP
multicast group membership. Users do not have to manually send IGMP messages.
Over time, the IETF has defined three versions of IGMP:
IGMPv1: IETF Request for Comments 1112 (RFC 1112) defines the original version of IGMP. RFC 1112
defines the join message that hosts use to join an IP multicast group. However, IGMPv1 does not define
a method for hosts to leave a multicast group. With IGMPv1, routers must use a timer to determine which
hosts are still members of the group.
IGMPv2: RFC 2236 defines �??group leave�?? messages that enable IP multicast-aware devices to keep
current information on group membership.
IGMPv3: RFC 3376 represents a major revision of IGMP. Instead of the one-transmitter/many-receiver
model of IGMP versions 1 and 2, hosts using IGMPv3 specify lists of transmitters to listen to.
IGMP snooping, as the name implies, is a method by which Layer 2 devices can �??listen in�?? on IGMP
conversations between hosts and routers. When a switch hears a group join message from a host, it
notes which switch interface it heard the message on, and adds that interface to the group. Similarly,
when a Layer 2 switch hears a group leave message or a response timer expires, the switch will remove
that host�??s switch interface from the group.
IP multicast traffic has some special characteristics. Destination IP addresses for multicast traffic fall
within the range of 224.0.0.1 through 239.255.255.255 (although some addresses within this range are
reserved). Destination Ethernet addresses for multicast traffic begin with 01:00:5E and end with the loworder
23 bits of the destination IP address.
Proposed Solution
Overview
Configuring IGMP snooping is a simple two-step process on Dell PowerConnect 33xx switches. First you
must enable IGMP snooping, and then you enable filtering of multicast traffic. Two examples are given
here:
�?� Enabling IGMP snooping globally for all interfaces on a Dell PowerConnect 3348 switch
�?� Enabling IGMP snooping for interfaces of a selected VLAN on a Dell PowerConnect 3348 switch
While it is possible to restrict the scope of IGMP snooping by enabling it only on selected VLANs, it is a
much more common practice to enable IGMP snooping on all switch interfaces.
Note that at least one Layer 3 device must exist in the network for IP multicast and IGMP snooping to
work. Layer 2 switches by themselves cannot support IP multicast service.
Step-By-Step Instructions
1. To enable IGMP snooping for all switch interfaces, enter the following commands from the console:
Dell-3348> enable
Dell-3348# configure
Dell-3348(config)# ip igmp snooping
Dell-3348(config)# bridge multicast filtering
PowerConnect Application Note #18: Understanding IGMP Snooping
http://www.dell.com/networking 4
Dell-3348(config)# end
Dell-3348# copy running-config startup-config
This sequence puts the switch in executive mode; enters into configuration mode; enables IGMP
snooping globally; enables selective forwarding of multicast traffic; exits configuration mode; and saves
the running configuration.
2. To enable IGMP snooping for a given VLAN (we use VLAN ID 100 in this example), enter the following
commands from the console:
Dell-3348> enable
Dell-3348# configure
Dell-3348(config)# int vlan 100
Dell-3348(config-if)# ip igmp snooping
Dell-3348(config-if)# bridge multicast filtering
Dell-3348(config-if)# end
Dell-3348# copy running-config startup-config
This sequence puts the switch in executive mode; enters into configuration mode; selects VLAN 100 for
configuration; enables IGMP snooping on VLAN 100; enables selective forwarding of multicast traffic;
exits configuration mode; and saves the running configuration.
Conclusion
As described above, IGMP snooping can provide a simple yet effective means of reducing unwanted
traffic from the network. With IGMP snooping enabled globally, a Dell PowerConnect switch will forward
IP multicast traffic only to interfaces with group members attached.
This Application Note is for informational purposes only, and may contain typographical errors and technical inaccuracies. The
content is provided as is, without express or implied warranties of any kind. Information in this document is subject to change
without notice.
Trademarks used in this text: Dell, the DELL logo, and PowerConnect are trademarks of Dell Inc. Other trademarks and trade
names may be used in this document to refer to either the entities claiming the marks and names or their products. Dell Inc.
disclaims any proprietary interest in trademarks and trade names other than its own. © 2004 D

Comment on Post LASIK Thoughts by aa

aa — Fri, 25 Apr 2008 09:13:43 +0000

9873333333333300000000000009999999999990000000000000000000

Comment on Post LASIK Thoughts by aa

aa — Fri, 25 Apr 2008 09:13:19 +0000

PowerConnect Application Note #18 February 2004
http://www.dell.com/networking 1
Understanding IGMP Snooping
This Application Note relates to the following Dell PowerConnect�?� product(s):
�?� PowerConnect 33xx switches
Abstract
This Application Note explains how a feature called IGMP snooping can significantly reduce traffic from
streaming media and other bandwidth-intensive IP multicast applications. This document introduces the
IGMP protocol and provides step-by-step instructions for configuring Dell PowerConnect 33xx switches to
use IGMP snooping.
Applicable Network Scenarios
By default, layer 2 devices such as Dell PowerConnect 33xx switches treat IP multicast traffic in the same
manner as broadcast traffic �?? namely, by forwarding frames received on one interface to all other
interfaces. This may create excessive traffic on the network and degrade the performance of hosts
attached to the switches. Every frame received by each host generates an interrupt that the host must
process, robbing cycles that might instead be used by applications.
Layer 3 devices have less of a problem with rampant broadcast and multicast traffic because of their
ability to segment networks and forward traffic only to actual destination interfaces.
With Internet Group Management Protocol (IGMP) snooping, Layer 2 devices also can make intelligent
multicast forwarding decisions by examining the contents of each frame�??s Layer 3 IP header.
Consider the example of a heterogeneous Layer 2 and Layer 3 network that does not use IGMP snooping.
The figure below shows a simple network in which eight hosts connect to four Layer 2 switches. The
switches in turn connect to one router in the middle.
A
B
C
D
PowerConnect Application Note #18: Understanding IGMP Snooping
http://www.dell.com/networking 2
Now suppose Host A is an IP multicast transmitter and Hosts B and C are multicast receivers in the same
group as Host A. The router will correctly forward IP multicast traffic only to those segments with
registered receivers (Hosts B and C). However, the Layer 2 switches will flood the traffic to all hosts on all
interfaces.
A
B
C
D
The larger the network grows, the greater the performance impact of this extraneous multicast traffic.
Now we can see what happens with the addition of IGMP Snooping on the Layer 2 devices. Just as
desired, only hosts that are group receivers actually receive multicast traffic.
A
B
C
D
Technology Background
The Internet Engineering Task Force (IETF) defined IGMP as a means of associating groups of IP
multicast transmitters and receivers. Each member host of an IP multicast is either a transmitter or a
receiver.
A station that wishes to become a receiver sends an IGMP �??group join�?? message to that group�??s
transmitter. Each Layer 3 device that forwards an IGMP join message records the group ID and source
PowerConnect Application Note #18: Understanding IGMP Snooping
http://www.dell.com/networking 3
interface in its multicast forwarding table. When the transmitter sends IP multicast traffic, the Layer 3
device will then forward the traffic only to those interfaces from which it has received join messages.
Thus, the Layer 3 device forwards IP multicast traffic only to those hosts that have requested it.
Applications that use IP multicast, such as those involving streaming media, automatically handle IP
multicast group membership. Users do not have to manually send IGMP messages.
Over time, the IETF has defined three versions of IGMP:
IGMPv1: IETF Request for Comments 1112 (RFC 1112) defines the original version of IGMP. RFC 1112
defines the join message that hosts use to join an IP multicast group. However, IGMPv1 does not define
a method for hosts to leave a multicast group. With IGMPv1, routers must use a timer to determine which
hosts are still members of the group.
IGMPv2: RFC 2236 defines �??group leave�?? messages that enable IP multicast-aware devices to keep
current information on group membership.
IGMPv3: RFC 3376 represents a major revision of IGMP. Instead of the one-transmitter/many-receiver
model of IGMP versions 1 and 2, hosts using IGMPv3 specify lists of transmitters to listen to.
IGMP snooping, as the name implies, is a method by which Layer 2 devices can �??listen in�?? on IGMP
conversations between hosts and routers. When a switch hears a group join message from a host, it
notes which switch interface it heard the message on, and adds that interface to the group. Similarly,
when a Layer 2 switch hears a group leave message or a response timer expires, the switch will remove
that host�??s switch interface from the group.
IP multicast traffic has some special characteristics. Destination IP addresses for multicast traffic fall
within the range of 224.0.0.1 through 239.255.255.255 (although some addresses within this range are
reserved). Destination Ethernet addresses for multicast traffic begin with 01:00:5E and end with the loworder
23 bits of the destination IP address.
Proposed Solution
Overview
Configuring IGMP snooping is a simple two-step process on Dell PowerConnect 33xx switches. First you
must enable IGMP snooping, and then you enable filtering of multicast traffic. Two examples are given
here:
�?� Enabling IGMP snooping globally for all interfaces on a Dell PowerConnect 3348 switch
�?� Enabling IGMP snooping for interfaces of a selected VLAN on a Dell PowerConnect 3348 switch
While it is possible to restrict the scope of IGMP snooping by enabling it only on selected VLANs, it is a
much more common practice to enable IGMP snooping on all switch interfaces.
Note that at least one Layer 3 device must exist in the network for IP multicast and IGMP snooping to
work. Layer 2 switches by themselves cannot support IP multicast service.
Step-By-Step Instructions
1. To enable IGMP snooping for all switch interfaces, enter the following commands from the console:
Dell-3348> enable
Dell-3348# configure
Dell-3348(config)# ip igmp snooping
Dell-3348(config)# bridge multicast filtering
PowerConnect Application Note #18: Understanding IGMP Snooping
http://www.dell.com/networking 4
Dell-3348(config)# end
Dell-3348# copy running-config startup-config
This sequence puts the switch in executive mode; enters into configuration mode; enables IGMP
snooping globally; enables selective forwarding of multicast traffic; exits configuration mode; and saves
the running configuration.
2. To enable IGMP snooping for a given VLAN (we use VLAN ID 100 in this example), enter the following
commands from the console:
Dell-3348> enable
Dell-3348# configure
Dell-3348(config)# int vlan 100
Dell-3348(config-if)# ip igmp snooping
Dell-3348(config-if)# bridge multicast filtering
Dell-3348(config-if)# end
Dell-3348# copy running-config startup-config
This sequence puts the switch in executive mode; enters into configuration mode; selects VLAN 100 for
configuration; enables IGMP snooping on VLAN 100; enables selective forwarding of multicast traffic;
exits configuration mode; and saves the running configuration.
Conclusion
As described above, IGMP snooping can provide a simple yet effective means of reducing unwanted
traffic from the network. With IGMP snooping enabled globally, a Dell PowerConnect switch will forward
IP multicast traffic only to interfaces with group members attached.
This Application Note is for informational purposes only, and may contain typographical errors and technical inaccuracies. The
content is provided as is, without express or implied warranties of any kind. Information in this document is subject to change
without notice.
Trademarks used in this text: Dell, the DELL logo, and PowerConnect are trademarks of Dell Inc. Other trademarks and trade
names may be used in this document to refer to either the entities claiming the marks and names or their products. Dell Inc.
disclaims any proprietary interest in trademarks and trade names other than its own. © 2004 Dell Inc. All rights reserved.

Comment on Thanks Austin. by aa

aa — Thu, 24 Apr 2008 06:44:47 +0000

Delete Lasik queery ASAP

Thanks

Comment on Post LASIK Thoughts by sumat

sumat — Thu, 24 Apr 2008 06:38:25 +0000

How to delete the comments from your web page

Comment on Post LASIK Thoughts by vv

vv — Thu, 24 Apr 2008 06:36:57 +0000

This is with reference to the Lasik Eye , as I had already performed the operation with specialized doctor .Below are the observation after Lasik :\
Right Eye
Vision Ok after Lasik i.e 10 min
After 72 hrs Vision without Glasses : 6/6 and with Pin hole 6/6
Left Eye
Vision was hazy..Putting drops prescribed by doctor.
But after 72 hrs after surgery
Vision without Glasses : 6/18 and with Pin hole 6/9.
As per doctor , there is swelling in an eye.Bcz of this hazy behavior was observed .
Please suggest is something is wrong happened in that eye.
Can there will be any possibilities for getting back my vision in OK .
Also Laser can be reversed
Can I wear glasses in such case or not .
Is there is any surgery required to improve the same.
After putting drops I am able to see good result ..that means vision is there in mine eye but something is focusing to get better result.
Please help me I am looking your assistance in this regards
Thanks for your help .