Migrate one single switch to two switches

[abimadaro4462]

Hello,

We have one single switch acting as a gateway for our campus network, with OSPF. The plan is to migrate this switch to two NEXUS switches with vPC configured along with HSRP (another suggestions are welcomed).

Please advise about the best way to migrate seamlessly with the lowest downtime.

Regards,

[Seb Rupik · Accepted solution]

Hi there,
Regarding the Layer2 config, establish a trunk link which trunks the common VLANs between the single switch and Nexus. Configure the HSRP on the Nexus such that they are in the same group but with the Nexus having the lower priority.

As for the Layer3 create a point to point link between the switch and Nexus. Ensure that they form an OSPF adjacency with eachother and that the Nexus is peered with the other routers in the area.

One by one start shutting down the Layer3 'inside' interfaces on the single switch, this will cause the Nexus to become the HSRP active router for that LAN segment. The point to point link will allow outbound traffic to reach the single switch and leave via the attached gateway.

Once all internal interfaces have been shutdown on the single switch, physically move the outbound link onto the Nexus. Remove the configuration advertising the default route into OSPF from the single switch, and migrate the config onto the Nexus.

Finally remove the trunk link between the two switches.

cheers,
Seb.

[abimadaro4462]

Hello,

Thanks for your detailed answer, but can you please clarify the point related to the HSRP as I didn't get it "Configure the HSRP on the Nexus such that they are in the same group but with the Nexus having the lower priority."

Regards,

[abimadaro4462]

Please note that the single switch is not Cisco one, so we wont be able to configure HSRP with the new Cisco one, If that's your point.

[Seb Rupik]

hmmm, that makes it a little more tricky. Since you want to retain the gateway for each VLAN during the migration, the best you can achieve would be to configure the HSRP and SVIs on the Nexus, and as you shut the SVIs on the single switch no shut the corresponding interfaces on the Nexus. You will experience some dropped packets during the transition so it would be best to attempt this during an out of hours maintenance window.

cheers,

Seb.