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Cisco router and HP switches. Not playing nice VLAN connectivity

Occasional Visitor

Cisco router and HP switches. Not playing nice VLAN connectivity

Hi, I just installed a cisco 1921 ISR router with 4 port 10/100/1000 switch module and stacked a Procurve 3500yl and Procurve 2910al L3 switch. I am including a diagram of the basic logical network.

I have setup the routers 4 port switch module in 802.1Q trunk mode with all 4 ports defaulting to VLAN 5 and gave it an IP of I am using module interface 0/1 to connect to 23 and 24 on the 3500yl and interface 2/3 to connect to the 2910al. I enabled spanning tree and created 1 lacp trunk group on both switches for this traffic.

On the 3500yl I enabled routing and set the default gateway to I set an IP address for each VLAN on the 3500yl. I created a 2nd static lacp trunk group and attached it to the 2910al.

On the 2910al I configured 1 static lacp trunk group for the router and a 2nd static lacp trunk group for traffic coming from the 3500yl. I set the default gateway to point to the 3500yl.

In this configuration I can ping the gateway but cannot connect to the internet. The furthest I have gotten was getting VLAN 5 up on the internet from some workstations but not others I lost that configuration shortly afterwards trying to get VLAN 5 working on all workstations.

I am getting a lot of syslog entries. I dont know if I have created a loop or if MSTP just creates a lot of information logs.

Hopefully someone with more experience can point me in the right direction. Thank you in advance for taking the time to read my post.

Antonio Milanese
Trusted Contributor

Re: Cisco router and HP switches. Not playing nice VLAN connectivity


could you post config cisco/procurve lines related to (M)STP, LACP/channel group,and trunk (i mean cisco lingo).

Are you using PSVT or regular MSTP?
When you say "defaulting to VLAN 5" do you mean that on both sides is the "access" untagged vlan?
Is the channel configured as trunk and vlan1 not allowed?
Which version of IOS and HP firmware?


first DON'T USE static trunks (there is nothing as static LACP, LACP relays on PDU exchange) so double check LACP settings or you have a half/flapping LACP group where traffic is discharged on member interfaces randomly when balancing hash does not match on both sides.

second: check if native VLAN (VLAN1 if not changed) is not blocked on CST and the CST root priority are correct expecially if you have PSVT since compatibility STP BDPUs are exchanged on native vlan.