Catalyst 3850 Cross-Stack EtherChannel

adimakmur · ‎10-15-2014

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.

glen.grant · ‎10-16-2014

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 .

adimakmur · ‎10-16-2014

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.

aukhadiev · ‎10-17-2014

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

adawa · ‎10-16-2014

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.

adimakmur · ‎10-16-2014

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