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Catalyst 3850 Cross-Stack EtherChannel

On 3850 configuration guide, I came across PAgP desirable mode is not supported in the switch stack (cross-stack EtherChannel).

http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3850/software/release/3se/layer2/configuration_guide/b_lay2_3se_3850_cg/b_lay2_3se_3850_cg_chapter_0101.html

 

But on Q&A document, it mentioned 3850 supports PAgP.

Q.    What cross-stack EtherChannel link bundling protocols are supported?

A.     The Cisco Catalyst 3850 supports Cisco Port Aggregation Protocol (PAgP) and industry-standard IEEE 802.3ad Link Aggregation Control Protocol (LACP). Other 3750 Series Switches support only LACP for cross-stack EtherChannel.
 

 

Seems like both statements are contradicting.

 

Can someone shed some light on this?

 

Thank you.

 

 

5 REPLIES
Purple

    the statement is correct

    the statement is correct , the switch supports both etherchannel protocols  you just can't use pagp if you plan on doing a cross stack etherchannel.  if using pagp then both ports would have to be off the same switch in the stack , if you want to spread the channel across mutliple switches in the stack then you can only use LACP.  Have no idea why they developed it like that .

New Member

Hi glen.grant,Thank you for

Hi glen.grant,

Thank you for your reply. This pagp limitation also applied to 3750 cross-stack etherchannel as well. Thought Cisco has made some improvements to 3850 to overcome this.

 

If you read through these two Q&A for 3850 (cross-stack etherchannel) below, don't you think pagp supports cross-stack etherchannel.

Q.    What types of EtherChannel capability are supported on Cisco Catalyst 3850 Series Switches?
A.     The Cisco Catalyst 3850 Series is supported on two different modes:

   Single-chassis EtherChannel: In this EtherChannel configuration mode, all the member links of given EtherChannel on single stack-switch system.

   Cross-stack EtherChannel: In this EtherChannel configuration mode, the member links are diversified between stack switches regardless of their roles.

 

Q.    What cross-stack EtherChannel link bundling protocols are supported?
A.     The Cisco Catalyst 3850 supports Cisco Port Aggregation Protocol (PAgP) and industry-standard IEEE 802.3ad Link Aggregation Control Protocol (LACP). Other 3750 Series Switches support only LACP for cross-stack EtherChannel.
 
Bronze

Hi, adimakmur Cisco Catalyst

Hi, adimakmur 

Cisco Catalyst 3850 Cross-Stack EtherChannel can be PAgP+ and can be used for VSS dual active detection.

In last deployment of 3850 we use Cross-Stack EtherChannel and use it as trusted for VSS dual active detection.

c6500-V#sh switch virtual dual-active pagp

PAgP dual-active detection enabled: Yes
PAgP dual-active version: 1.1

----skiped----

Channel group 106 dual-active detect capability w/nbrs
Dual-Active trusted group: Yes
          Dual-Active     Partner              Partner   Partner
Port      Detect Capable  Name                 Port      Version
Te1/7/7   Yes             c3850-307            Te1/1/3   1.1
Te2/7/7   Yes             c3850-307            Te2/1/3   1.1

 

---skiped----

c6500-V#sh etherchannel 106  protocol 
Protocol:  PAgP

c3850-307#sh etherchannel port-channel 
                Channel-group listing: 
                ----------------------

Group: 1 
----------
                Port-channels in the group: 
                ---------------------------

Port-channel: Po1
------------

Age of the Port-channel   = 235d:20h:50m:10s
Logical slot/port   = 12/1          Number of ports = 2
GC                  = 0x00010001      HotStandBy port = null
Port state          = Port-channel Ag-Inuse 
Protocol            =   PAgP
Port security       = Disabled

Ports in the Port-channel: 

Index   Load   Port     EC state        No of bits
------+------+------+------------------+-----------
  0     00     Te1/1/3  Desirable-Sl       0
  0     00     Te2/1/3  Desirable-Sl       0

Time since last port bundled:    169d:04h:58m:49s    Te1/1/3
Time since last port Un-bundled: 169d:05h:00m:47s    Te1/1/3

 

Bronze

Hello, adimakur. Glen is

Hello, adimakur. 

Glen is correct, Cisco 3850 supports both protocols. Is this for your existing 3850 switches that you are looking to cross stack?

Kind regards. 

New Member

Yes, planning to do cross

Yes, planning to do cross-stack etherchannel for 3850.

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