Wired Intelligent Edge

I want to build a new 'core' for our network. We currently have a 3com 4060 switch acting as the core, connecting all the other TOR and access switches together.

The goal is to add resilience into the core, without compromising performance.

Each switch currently connects to the core with between 2 and 4 physical links configured as LACP trunks.

I am looking at replacing the 3com with a pair of HP 2920 switches with the optional stacking module. My understanding is that with the stacking module, the 2 switches will act as 1 'virtual' switch so I can connect each link from the access switches to each 2920:

http://i.imgur.com/03IP2Gf.png

(For some reason I can't actually insert the picture here; Flash + Linux isn't the greatest)

The actual question

I know this isn't an unusual arrangement, but my questions are:

1. Can it be done with the HP 2920 switches?
2. Should I be using the HP "Trunk" type of trunk instead of LACP?

3. Am I going about this completely wrong?

I've found a lot of conflicting information. A lot of sources say that either Distributed Trunks can only be done with 3xxx or higher switches but the HP QuickSpecs say that DT is possible with the 2920. Other sources say that DT can only be done between a pair of switches and a server (not other switches) but if the DT appears as a LACP trunk to the 'downstream' device then how does it matter?

I could do this using STP to block the links between the access switches and the second core switch, but I don't want to waste all that bandwidth.

According to this HP Forum thread. Full stacking is supported on the 2920. You can create manual LACP trunks spanning both 2920 switches to your downlevel switches.

Thanks Acmosa, I didn't see that thread in my searching. The way I read it though, they are talking about trunks to servers, not between switches, which is what I've read can't be done: http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?lang=en&cc=us&taskId=110&prodSeriesId=3897494&prodTypeId=12883&objectID=c03269076

Yes, it is confusing because originally it was implemented as DT for servers only not switch-switch links.

On the 5400s, after about K1508, it became supported on switch-switch links.

So what you need to do is navigate HPs website and find the very latest config guide for the latest firmware version for your switch and find the chapter on DT to see what it says.

Honestly, whoever is in charge of HP's website needs a kick up the arse.

Why does it take so long to find things?

This manual is less than 6 months old:

http://h20628.www2.hp.com/km-ext/kmcsdirect/emr_na-c03673787-2.pdf

The section on link aggregation doesn't mention DT. That would normally suggest to me that the firmware used on 2920s doesn't support it at all.

However, the data sheet says,

So, in conclusion, *maybe* they support it, but it's not properly documented as far as I can see.

1. Can it be done with the HP 2920 switches? YES
2. Should I be using the HP "Trunk" type of trunk instead of LACP? For the stacking, this is irrelevant. For aggregated links to other devices, LACP is usually best.

3. Am I going about this completely wrong? NO, exactly on the right track.

Note that distributed trunking has nothing to do with the 2920 switches. 2920 switches have a stacking module with 2 40Gb ports that allow up to 4 2920 to be linked together into a single device. MLAGs are possible (eg LACP from ports 1/1 and 2/1 to an external switch, server, etc). When you connect the switches via the stacking modules and cable, it looks to the rest of the world like a single device. Very easy!

Sample config from 2920-stack included:

; hpStack_WB Configuration Editor; Created on release #WB.15.11.0003
; Ver #03:12.15.0d:09

stacking
   member 1 type "J9727A" mac-address d89d67-8af040
   member 2 type "J9727A" mac-address d89d67-863dc0
   exit
hostname "2920-stack"
trunk 1/A1,2/A1 trk1 lacp
trunk 1/A2,2/A2 trk2 lacp
gvrp
logging 10.20.30.85
timesync sntp
sntp unicast
sntp server priority 1 10.20.30.90
time daylight-time-rule user-defined begin-date 10/01 end-date 04/01
time timezone 600
ip authorized-managers 10.20.30.0 255.255.255.0 access manager
ip authorized-managers 10.20.248.0 255.255.254.0 access manager
ip default-gateway 10.20.30.2
ip ssh filetransfer
interface 1/24
   name "Spanning tree test"
   exit
interface 1/A1
   name "Link to 5830"
   exit
interface 2/A1
   name "Link to 5830"
   exit
snmp-server community "public" operator
snmp-server community "private" unrestricted
snmp-server host 10.20.30.85 community "public"
oobm
   ip address dhcp-bootp
   member 1
      ip address dhcp-bootp
      exit
   member 2
      ip address dhcp-bootp
      exit
   exit
vlan 1
   name "DEFAULT_VLAN"
   no untagged 1/1-1/18,1/23-1/24,Trk1-Trk2
   untagged 1/19-1/22,1/B1-1/B2,2/1-2/24,2/B1-2/B2
   no ip address
   exit
vlan 200
   name "Exhibition Connectivity"
   no ip address
   forbid 1/23-1/24
   exit
vlan 930
   name "Servers"
   untagged Trk1-Trk2
   ip address 10.20.30.20 255.255.255.0
   exit
vlan 1248
   name "Roadshow demo"
   untagged 1/1-1/18,1/23-1/24
   no ip address
   exit
spanning-tree
spanning-tree Trk1 priority 4
spanning-tree Trk2 priority 4
spanning-tree config-name "Roadshow"
spanning-tree config-revision 1
spanning-tree priority 4
no tftp client
no tftp server
no autorun
no dhcp config-file-update
no dhcp image-file-update
password manager

@Richard Litchfield Awesome answer, just what I was after. Thank-you very much! :D

Now I just need to get the boss to approve the purchase, I will report back with my results :)

Well the boss approved it, and I installed it last weekend. Everything works perfectly.... Good-bye to the old 3com and Hello to managability and room for expansion :D

Thanks again to those who helped clarify my questions around this :)