two uplinks between two switches

[franchesco_alba]

Hi,

I would like to configure two uplink cable to connect two switches, one uplink cable to uplink vlan1 and other uplink cable to vlan50. But when I connect the second cable in vlan50, the network comes down.

Should I configure something else ?

[Ian Vaughan]

Howdy,

A handful of questions first:

1) what types of switches are we dealing with here?

2) Do you have admin access to the switches either through Command line or web session (it sounds like you do)?

3) Do you want seperate uplinks for the 2 VLANs or would you be happy with one physical link that carries both?

You are probably creating a network loop when you plug in the second cable. Be easier to "piggy back" the new VLAN 50 on the existing uplink that carries VLAN 1 - do a search for  "tagged and untagged" VLANs if you are on Procurve/Aruba-OS or look for VLAN trunk if you have seen reference to Comware OS .

If you can give us a bit more info as per questions above we should be able to help.

Thanks

Ian

## (Hope this helps - kudos button below if it did)  ##

[franchesco_alba]

Hi lan,

1 ) It's between HP  V1910-24G and 3COM 2928 24P.

2) Yes, I do. I have web access and command line.

3) I want separate uplink for 2 vlans, one of vlan I will use for ISCSI network. I would like to enable jumbo frame on vlan 50. I will use the vlan 50 to destination of my backup, because it I would like use 2 uplinks,.

Thank you.

[Ian Vaughan · Accepted solution]

Howdy,

Those particular switches do not have huge buffers and 1GbE iSCSI really tops out at around 100MB from the controller ports. So, you are never going to get screaming performance (like 10GbE on a deep buffer 5920) but you should get something respectable out of them. :-)

Remember to switch on jumbo frames and you should also be able to do things like enable flow control and you can even prioritise the traffic using QoS queues if you are sharing the ports for mixed workloads.

Firstly you probably need to get familiar with using spanning tree (especially MSTP variety) for loop prevention.

I'm guessing your network falls over / jams up with traffic when you plug the second connection in. One of the switches might have MSTP switched on and all VLANs are (by default) in the default MST instance essentially making it one logical topology despite the different VLANs. I'm guessing that the other switch has Spanning tree switched off or else I think it would recognise the loop and at least block one of the ports from forwarding to stop the traffic storm.

In either case what you really need is: 

The 2 switches to have the 2 vlans configured and each switch to have 2 configured & enabled and matching MST instances.

The first instance (the default one) will contain every VLAN apart from VLAN 50 and then VLAN 50 will be mapped into instance 2.

This allows 2 uplinks between switches without loops and without ports becoming blocked as part of the loop prevention mechanism. I would configure the uplinks as "trunk" interfaces to give you a bit of freedom in the future.

I usually recommend migrating "normal" network traffic off VLAN 1 becasue there can be security issues using this for production traffic. It can help if you put PROD on say VLAN 10 and only use VLAN 1 for inter-switch management traffic etc. You can then still use vlan1 as the "PVID" for your trunks  - (google it if this terminology is new).

iSCSI interfaces should each have their own IP address - let the MPIO drivers on the hosts sort out the multipathing. Read the vendor's best practice guide for how to set up the connectivity some like to have 2 vlans of 2 interfaces, some don't seem to care.

You can use LACP to aggregate a couple of the uplinks together (google it) if you want to give more inter-switch bandwidth to VLAN50. iSCSI uses different TCP ports so should hash nicely over the connections as long as you have more than one traffic stream and you use the right hashing option (source MAC if TCP port not available) on the aggregate link.

Phew - hope that helps - please hit the kudos button if it does.

Thanks

Ian