pagp auto silent mode

Answered Question
Jul 1st, 2008

hi every body!

I have just one question with regard to pagp auto silent mode.

As far as i understand, pagp auto silent mode tells the switch wait for 15 seoonds for pagp packets, if you dont receive any with in that time, you could go ahead , and put this port in bundle.

I know if two switches are connected together by links, if we wish to form etherchannel on those ports , we cant use pagp auto silent mode on either ends.

But why? theortically, each port configured with pagp auto silent mode should wait for 15 seconds to recive any pagp packets , if none received, the port should be put in bundle.

I will really appreciate your guys help.

thanks and have a nice day !

I have this problem too.
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Correct Answer by Edison Ortiz about 8 years 6 months ago

The point is if we use pagp auto silent mode on two switches, ether channel should form

It does as that's the default setting (silent).

I addressed that in my post.

__

Edison.

Correct Answer by Edison Ortiz about 8 years 6 months ago

I posted this information a while back and I believe it's useful to this thread

Silent/Non-Silent Mode

When you deal with fiber connections, there is a possibility that, even if a receive (Rx) transceiver dies, the transmit (Tx) transceiver on the other end is still up. In a similar scenario, packets can get black holed.

It is important for the switch that transmits to remove this port from the EtherChannel bundle. In order to do so on the Catalyst 5500/5000, you set PAgP in non-silent mode. Non-silent mode means that, if the Rx does not receive traffic, the port is not put into the channel. However, use of non-silent mode is not enough because this detection happens only when the channel is formed.

In order to prevent the black holing of traffic when the channel is already formed, this occurs:

1.

PAgP detects that the Rx port does not receive any traffic.

2.

PAgP resets the Tx transceiver of the port that does not receive traffic. PAgP resets it for 1.6 seconds so that the switch on the other end also resets the port.

3.

The faulty port does not join the channel anymore because no traffic is received on that port.

On the Catalyst 5500/5000, set non-silent mode on fiber strands and silent mode on copper strands. This is both the default and recommended setting because, on fiber connections on the Catalyst 5500/5000, the negotiation is usually not available, so there is no way to detect the problem at a physical layer.

Default PAgP Settings on the Catalyst 4500/4000 and 5500/5000

By default, PAgP is auto for a plug-and-play implementation. Disable PAgP manually from the ports where there is no need to have it.

By default, the silent mode is on. Non-silent is acceptable as well. However, because a port can be connected to a device that does not send traffic (for example, a sniffer), it is more general to have silent enabled.

Recommendations

*

Use the non-silent keyword when you connect to a device that transmits bridge protocol data units (BPDUs) or other traffic. Use this keyword with the auto or desirable mode. PAgP non-silent adds an extra level of link state detection because it listens for BPDUs or other traffic in order to determine if the link functions properly. This adds a form of UniDirectional Link Detection (UDLD) capability that is not available when you use the default silent PAgP mode.

*

Use the silent keyword when you connect to a silent partner (which is a device that does not generate BPDUs or other traffic). An example of a silent partner is a traffic generator that does not transmit packets. Use the silent keyword with auto or desirable mode. If you do not specify silent or non-silent, silent is assumed.

*

The silent mode does not disable the PAgP ability to detect unidirectional links. However, when you configure a channel, non-silent prevents a unidirectional port from even joining the link.

*

A PAgP configuration (the set port channel {desirable | auto} command) is safer than a non-PAgP configuration (the set port channel on command). A PAgP configuration provides protection for unidirectional links and also avoids misconfigurations that can arise when there are ports channeling on one side of the link and not on the other side.

*

Refer to Understanding and Configuring the Unidirectional Link Detection Protocol Feature for more information on UDLD.

HTH,

__

Edison.

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owillins Mon, 07/07/2008 - 05:48

pagp auto silent mode

Places an interface into a passive negotiating state, in which the interface responds to PAgP packets it receives but does not start PAgP packet negotiation. This setting minimizes the transmission of PAgP packets.

Correct Answer
Edison Ortiz Mon, 07/07/2008 - 07:36

I posted this information a while back and I believe it's useful to this thread

Silent/Non-Silent Mode

When you deal with fiber connections, there is a possibility that, even if a receive (Rx) transceiver dies, the transmit (Tx) transceiver on the other end is still up. In a similar scenario, packets can get black holed.

It is important for the switch that transmits to remove this port from the EtherChannel bundle. In order to do so on the Catalyst 5500/5000, you set PAgP in non-silent mode. Non-silent mode means that, if the Rx does not receive traffic, the port is not put into the channel. However, use of non-silent mode is not enough because this detection happens only when the channel is formed.

In order to prevent the black holing of traffic when the channel is already formed, this occurs:

1.

PAgP detects that the Rx port does not receive any traffic.

2.

PAgP resets the Tx transceiver of the port that does not receive traffic. PAgP resets it for 1.6 seconds so that the switch on the other end also resets the port.

3.

The faulty port does not join the channel anymore because no traffic is received on that port.

On the Catalyst 5500/5000, set non-silent mode on fiber strands and silent mode on copper strands. This is both the default and recommended setting because, on fiber connections on the Catalyst 5500/5000, the negotiation is usually not available, so there is no way to detect the problem at a physical layer.

Default PAgP Settings on the Catalyst 4500/4000 and 5500/5000

By default, PAgP is auto for a plug-and-play implementation. Disable PAgP manually from the ports where there is no need to have it.

By default, the silent mode is on. Non-silent is acceptable as well. However, because a port can be connected to a device that does not send traffic (for example, a sniffer), it is more general to have silent enabled.

Recommendations

*

Use the non-silent keyword when you connect to a device that transmits bridge protocol data units (BPDUs) or other traffic. Use this keyword with the auto or desirable mode. PAgP non-silent adds an extra level of link state detection because it listens for BPDUs or other traffic in order to determine if the link functions properly. This adds a form of UniDirectional Link Detection (UDLD) capability that is not available when you use the default silent PAgP mode.

*

Use the silent keyword when you connect to a silent partner (which is a device that does not generate BPDUs or other traffic). An example of a silent partner is a traffic generator that does not transmit packets. Use the silent keyword with auto or desirable mode. If you do not specify silent or non-silent, silent is assumed.

*

The silent mode does not disable the PAgP ability to detect unidirectional links. However, when you configure a channel, non-silent prevents a unidirectional port from even joining the link.

*

A PAgP configuration (the set port channel {desirable | auto} command) is safer than a non-PAgP configuration (the set port channel on command). A PAgP configuration provides protection for unidirectional links and also avoids misconfigurations that can arise when there are ports channeling on one side of the link and not on the other side.

*

Refer to Understanding and Configuring the Unidirectional Link Detection Protocol Feature for more information on UDLD.

HTH,

__

Edison.

sarahr202 Wed, 07/09/2008 - 19:01

thanks for reply Edison . The point is if we use pagp auto silent mode on two switches, ether channel should form ( i know this is not case in reality)because pagp silent mode instructs switch to form channel even if none received so two switches with auto pagp silent configuration should form ether channel.

I really appreciate if someone can elaborate on it.

thanks

Correct Answer
Edison Ortiz Wed, 07/09/2008 - 19:06

The point is if we use pagp auto silent mode on two switches, ether channel should form

It does as that's the default setting (silent).

I addressed that in my post.

__

Edison.

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