redundancy setup

[Shibu1978]

Hi,

I need some clarifications to design the network with below requirements .

Current Situation

============

We are able to reach server IP -10.203.206.40  from our 4948 switch vlan 10.30.1.0/24 through the Layer 3 interface between 4506 and 4948.  

Requirements

==========

1) Now we would like to add one more L3 interface between 4506 & 4948 for redundancy purpose.

2) Make available Vlan 540 in 4948  from 4506... need to create two trunk links between 4506 & 4948 and allow vlan 540.

I have attached the current setup.

Kindly guide me if its doable with no switching loop.

Thanks

[Jon Marshall]

Can you post diagram as jpeg as not all of use have visio available.

Jon

[srikanth ath]

           

Hello Jon,

here is the JPEG file.

Regards,

srikanth

[Jon Marshall]

Srikanth

1) Yes, very straighforward, just create new L3 link between 4506 and 4948 backup switches

2) do you need vlan 540 to actually be extended to the 4948 or do you just need to route to it ? If you need to extend it then you need L2 link(s) between the 4848 and 4500 switches and STP will block one of the links.

Jon

[Hari Vishnu]

Hi,

As you have mentioned Vlan 540 should be available in SW 4948, obviously you need L2 trunk link between the switches. That implies you need to remove the existing L3 link (10.30.255.0/30).

Thanks

H

[Shibu1978]

Thanks to all.

I have attached the proposed and current diagram with the details.

Hi John,

1) Yes, very straighforward, just create new L3 link between 4506 and 4948 backup switches

Yes we would create L3 link between 4506 and 4948 switches. we will do the neccessary redistribution over ospf  and routing on the backup 4506 switches. this part is clear and i hope this will work as we expect.

2) do you need vlan 540 to actually be extended to the 4948 or do you just need to route to it ? If you need to extend it then you need L2 link(s) between the 4848 and 4500 switches and STP will block one of the links.

I need to extend the vlan 540 to 4948 from 4506.   Inoder to have backup we have to do L2 trunk between 4506 primary to 4948 primary similiarly 4506 backup to 4948 backup.

Once you have all the connections in place you will 2 each connections from 4506 primary  to 4948 primary ( 1 L3 & 01 L2 trunk)  & 2 from 4506 backup to 4948 primary( 1 L3 & 01 L2 trunk)

Since we have 2 connections each from switch i guess STP will block one link per switch.   so i cant use both connections in a switch . now i need to use one L3 link and one L2 trunk link between switch ...other connections keep it handy for emergency situation to manually plug in.

Hope i made it clear now

Jon

[Jon Marshall · Accepted solution]

Since we have 2 connections each from switch i guess STP will block one link per switch. so i cant use both connections in a switch . now i need to use one L3 link and one L2 trunk link between switch ...other connections keep it handy for emergency situation to manually plug in

Not quite right.  Both L3 links will be up and forwarding. One of the L2 links will be blocked by STP. So you will have 3 links up and running with one L2 link blocked. STP only blocks L2 links.

The L2 links you add for vlan 540 do not  need to be trunks, unless you want to extend other vlans. They only need to be switchports in vlan 540. STP, as discussed, will block one of the links.

If you find you need to extend more vlans between the 4500 and 4948 switches then using L3 links as you are currently is probably not the right design choice. You may want to simply change the L3 links to L2 trunks. It really depends on what else you have on the 4948 switches in terms of vlans but it's not possible to be more specific as there is not enough detail from the diagrams in terms of vlans/subnets in use.

*** Edit - you should be able to have all these links plugged in and STP will block one of the L2 links ie. there should be no need to manually plug anything in if a link fails for example.

Jon

[Shibu1978]

Since we have 2 connections each from switch i guess STP will block one link per switch. so i cant use both connections in a switch . now i need to use one L3 link and one L2 trunk link between switch ...other connections keep it handy for emergency situation to manually plug in.

Jon -   Not quite right.  Both L3 links will be up and forwarding. One of the L2 links will be blocked by STP. So you will have 3 links up and running with one L2 link blocked. STP only blocks L2 links

Thanks a ton for the clarifications. i was in the impression that only one L3 interface would be active anf forwading traffic.

Jon : -  The L2 links you add for vlan 540 do not  need to be trunks, unless you want to extend other vlans. They only need to be switchports in vlan 540. STP, as discussed, will block one of the links

On the 4948 we are going to have 5+ servers on the vlan 540.. this can only achive using the link between 4506 to 4948 as trunk. hence we have trunk link.

Jon: If you find you need to extend more vlans between the 4500 and 4948 switches then using L3 links as you are currently is probably not the right design choice. You may want to simply change the L3 links to L2 trunks. It really depends on what else you have on the 4948 switches in terms of vlans but it's not possible to be more specific as there is not enough detail from the diagrams in terms of vlans/subnets in use.

We dont want to extend  more vlan between switches.

Since there is no routing protocols running in both 4948 switches we have this L3 interfaces to interconnect with 4506 switches.  then redistributing the subnet( 10.30.1.0/24) over ospf in 4506 and reaching the final point.

Hope made it clear...thanks

[Jon Marshall]

On the 4948 we are going to have 5+ servers on the vlan 540.. this can only achive using the link between 4506 to 4948 as trunk. hence we have trunk link.

It's nothing to do with how many servers you have, it is to do with how many vlans. If you only want to pass one vlan across the link ie. vlan 540 then it does not need to be a trunk. A trunk link is used to pass multiple vlans down the same link. If you only want to pass traffic for vlan 540 then the port config on both switches would look like -

int gi/??

switchport

switchport mode access

switchport access vlan 540

this way you have only extended vlan 540 between the 4500s and the 4948s.

Jon

[Shibu1978]

Thanks for you reply.

Meanwhile let me make it very clear now. please i have the following connectivity diagram for vlan 540...

Hope i am not dragging it

[Jon Marshall]

Your config is fine but i say again, if you only need to extend vlan 540 then it does not need to be a trunk. You would only need a trunk if you needed to extend more than one vlan. It has nothing to do wit how many ports you assign into vlan 540 on the 4948 switches.

You can use a trunk if you want but i would only use a trunk if i needed to carry multiple vlans down that link and in your case you don't but it would still work fine with a trunk link.

Jon

[Shibu1978]

Thanks a lot.

As advised let me connect all the four connections ( 2 L3 & 2 L2 trunk) between switches and check the status and connectivity. will update you

Thanks again

[Jon Marshall]

No problem.

One last point. If you are extending vlan 540 to the 4948 switches then make sure you have set the STP priority on the 4500s for vlan 540 so that they remain the STP root and secondary for that vlan. You don't want the 4948s becoming the root and secondary for that vlan.

Also connecting up the L3 link will have no effect on downtime but connecting up the L2 links could well have an impact so dont do this during core production hours. If there is an impact it should only be a short one ie. less than a minute with standard STP and a lot less than that with RSTP/MST.

Jon

[Shibu1978]

Thanks

4506 is already acting as the root & secondary for the vlan 540.

[Jon Marshall]

Okay, hope it all goes well.

Jon