HP Switch connected to CISCO Switch Spanning tree

Jack-Black
Jack-Black used Ask the Experts™
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I have two Layer 3 HP procurve switches with spanning tree enabled and with multiple spanning tree instances enabled, the two switches are also with vrrp and provide gateway redundancy which works fine.

I need to connect the two procurve switches to a Cisco layer 3 core switch which links the site to a remote site.

Questions:
1) What do i have to do to make the hp spanning tree work with the cisco switch spanning tree?

2) Sine all the switches are doing routing and acting also as a router are they also blocking broadcasts ? is so shall i use the ip helper address command if yes why and how?
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Don JohnstonInstructor
Top Expert 2015

Commented:
1) Run 802.1s (MST) on the Cisco. (see below)

2) If you need to pass DHCP, NTP, TFTP, etc. traffic to another network, yes. The command is "ip helper-address <x.x.x.x>" where "x" is the destination you want the traffic forwarded to.

spanning-tree mode mst
spanning-tree mst configuration
name stewie
revision 10
instance 1 vlan 10-20
instance 2 vlan 21-30

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Commented:
Make sure the Cisco switches are not using "spanning-tree mode rapid-pvst"  Rapid-pvst is proprietary to Cisco
Don JohnstonInstructor
Top Expert 2015

Commented:
Hence the "spanning-tree mode mst" statement.

Author

Commented:
The problem is that i do not have access to the cisco switch, this is at a client and i am setting an iscsi network with vrrp using hp procurve switches. I have already set everything, including vrrp and mstp with two instances to distribute vlans, both are working great with fail-over and fail-back.

Now i realised that to set the mstp instances and vrrp i have set the Sw1 as the root and switch 2 is not, now when i go on site and  connect the two switches to the cisco core which most probably is the current root it might  influence my setup..actually i  think it sould not as i have set (remember these are HP switches)  spanningtree priority 0 on Sw1 and spanningtree priority 0 and 1 for the two instances on both.

So..
If i leave everything as is and do not touch the cisco switch will switch 1 still be elected as Root  or i will end up with two root switches and be subject to a loop?

If the cisco switch is running pvst or pvst+ or if i add the "spanning-tree mode mst"  will it be running more that one spanning tree protocol at the same time ? (i do not want to effect the other switches)

Thanks guys, for your help i am trying tothink of every thing in advance ..to prevent problems..so i you think i am missing some thing just let me know...
Instructor
Top Expert 2015
Commented:
>What do i have to do to make the hp spanning tree work with the cisco switch spanning tree?
>The problem is that i do not have access to the cisco switch

Then you can't make the two work together. Cisco doesn't do true 802.1d spanning-tree. The only compatible STP between the two vendors is 802.1s (MST). But that must be configured on the Cisco.

The HP switches will still function as they do now. The Cisco won't recognize the two HP switches and will assume the role of root. So basically, you'll end up with two roots.  I've played around with this type of topology in a lab environment and it can work. But it can also be unpredictable too.

The proper approach is to have the Cisco configured to do MST. Otherwise, all bets are off.

Author

Commented:
OK, i will ask them to set MST on the cisco swich, by any chance do you know if it is possible to run multiple spanning tree protocols on the cisco switch ?i mean  if they enable mstp will that disable pvst  or pvst+ or what ever they currently have or will it run in parallel ?
Don JohnstonInstructor
Top Expert 2015

Commented:
No. The STP is set globally on a Cisco switch.  

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