VLAN Trunk and routing questions

Hiya there,

I have 8 VLANS coming from my HP 6108 - 8 Port GB Switch

i have 2 HP 5412 Chassis' with CX4 interfaces

i want to take all 8 VLANS onto the chassis'.  i was wondering whether i would be better using 8 cables to go into the chassis and assigning each port to that VLAN.

vlan 1 untagged a1
vlan 2 untagged a2
vlan 3 untagged a3

so on and so forth...

or would i be better just setting up a 1 GB trunk link from the 6108 onto the chassis with all of them tagged.

Thats how i have the Chassis to Chassis link setup, i thought if its 10GB then it wont really make a difference that im taking all 8 over the link.

any comments?

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The big difference obviously is which I'm sure you are already aware, that if you use a 1Gbps uplink for 8 VLAN's, the 8 VLAN's share the 1Gbps of bandwidth to the 5412 whereas using 8 cables (1 for each VLAN) gives each VLAN 1Gbps of bandwidth.  This is okay for now with the 8 VLAN's but big drawback is if you keep adding VLAN's, you need a separate cable run and you burn two switch ports per VLAN.  Obviously this doesn't scale well.  I'm a "Cisco guy" so I don't claim to be an HP expert by any means but I would assume the HP's support etherchannel or bonding of switch ports.  I believe in HP speak it is an LACP trunk...?  What you could do is connect the 6108 to each 5412 using two or four ports/cables in LACP trunking mode and enable tagging.  Assuming you are running Spanning-Tree, you could make one 5412 the spanning tree root for VLAN's 1,3,5,7 and the other 5412 the spanning-tree root for VLAN's 2,4,6,8.  This means 4 VLAN's get 2 or 4 Gbps depending on how many ports you bundle/trunk.  Make sense or did I incoherently rant here?
chesterzooAuthor Commented:
no that sounds good, very clear and helpful thanks!

Anybody else have any opinions? not that i dont value yours i just wanted a few different opinions so i can weigh up the options?

The 'normal' setup would be to trunk the VLANs between the switches over one physical connection.
As JFrederick29 pointed out, this limits your backbone to 1Gbps.

If you need more bandwidth, look into Link Aggregation (LACP).
This takes multiple physical connections and bonds them into one logical connection.
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chesterzooAuthor Commented:
so am I right in saying if switch ports weren't at a premium everybody would go for 1 GB link per VLAN.

I just thought because I am using the 6108 as my backbone switch and it does my inter-vlan routing it would be best keeping the bandwidth as high as possible.

so could i just ask if i had 2 HP switches connected with 4 cores of fibre that could run at 100mb only, could i theoretically link both pairs using LACP and 2 sets of physical media converters?? thus making me have a 200mb link?
For most, a 1Gbps backbone is plenty, however "your mileage may vary".
You should be able to go into your switches and look at the bandwidth utilization.

200Mbps link?  Yes.
chesterzooAuthor Commented:
yeah that's a good idea, ill check out the current utilisation and have a look! :)

Cheers guys...
chesterzooAuthor Commented:
bandwidth varies a fair bit between the different switches and VLANS, so i think im best sticking to the 1gb per VLAN way of doing it... just to make sure i get that extra bit of bandwidth!

chesterzooAuthor Commented:
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