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Move L3 routing from 3750 to Nexus 5596

                   Could someone offer suggestions on the best methods for moving L3 routing from a 3750G stack to a pair of Nexus 5596 switches?  I realize there will be a maintenance window required.  Can I create the same SVI on the Nexus but keep the interface shutdown and when I'm ready to move the SVI, shut down the SVI on the 3750 and bring up the SVI on the Nexus?

Current 3750 configuration:

VTP server

SVI's for VLANs

Nexus 5596 configuration:

In a VPC domain, direct server attach, peer-keepalive between N5K1 and N5K2

feature interface-vlan (enabled)

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How is the 3750 going to be connected to the Nexus ?

Is the 3750 still going to be used simply as a L2 switch ?

If so yes you could create the SVI on the Nexus and leave it shutdown but when you brought it up you may well find that the clients have the old mac address to IP for their default gateway and this would need to be timed out or the clients rebooted so it could cause problems.

You could, if the 3750 was connected to the Nexus via a trunk link run HSRP between the SVIs on the 3750 and the Nexus and ensure that the SVI on the 3750 was the active gateway using a higher priority. Then you can simply shut down the SVI on the 3750, the virtual IP is moved to the Nexus and this would not interrupt traffic.

The problem with that though is you will still want to then remove the HSRP config, as it was only temporary, so you then face the same issue with the clients. That is the key issue really, you need to update the clients so they have the correct mac address for their default gateway.




You brought up an important point that I failed to give consideration to and at the same time forgot to mention.  The 3750G's (2) are currently in a port-channel to each Nexus 5596 with my default route on the N5K'2 pointing to the 3750.  I would like to keep the 3750's as L2 when the routing is moved.



Yes, i think as i said, your main issue is with the client arp tables when you migrate to the Nexus switches. If the 3750 is connected via a trunk i can't see any reason why you could not have the Nexus SVIs particpate in HSRP with the 3750 (although again i would stress i have not used Nexus switches) but even though that should allow you to migrate with little or no downtime, you still then have the problem of then removing the HSRP config once it isn't needed and moving the virtual IP to the actual physical interface.





I am in the same exact situation now, what did you end up doing?

Any tips?

My servers are conneced to a SAN via the core switch and I need to keep L3 functionality.


During the migration we had an issue leaving the old L3 3750's in place with the Nexus 5596's, I don't remember what it was but had to do with ARP and HSRP.  To solve that we disconnected the 3750's completely once the 5596's were up and running and refreshing ARP cache


One gotcha I also ran into was my Nexus config text file with my SVI's.  My SVI's dont run sequential meaning, I have VLAN's 5-12, 17-25, 30-40 etc.  When I pasted the config into the Nexus it created interface VLAN's 1-4, 13-16, 26-29 etc.  Minor annoyance when I'm doing a sh run


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