Cat 4500x VSS to standalone

[LandrinLong]

Hello,

We have two 6807 XL switches that are currently utilizing HSRP.  We had an outage that caused some unforeseen problems and the decision has been made to move to VSS.  I've been doing a lot of reading, research, and video watching and have yet to find an answer.  The current HSRP is between 15 different VLANs.  My question is, when we perform the configuration to enable VSS, how does it convert the HSRP configuration?  Will the VLANs just merge into one configurations with the virtual IP being the configured IP address, or will I have to reconfigure the VLANs so that my default gateways of all of the nodes do not have to be reconfigured?

[Leo Laohoo · Accepted solution]

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@LandrinLong wrote:

My question is, when we perform the configuration to enable VSS, how does it convert the HSRP configuration?

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When a pair is converted to VSS, the configuration of the "master" gets absorbed.  The configuration of the 2nd unit "goes away".  The secondary unit then downloads the configuration from the master and goes into hot standby.  

So if there is an HSRP configuration, the configuration will remain but there will be no "second" unit to do HSRP pairing with. 

Does this make sense?

[LandrinLong]

What do you mean by the second configuration "goes away"? Does that mean that the configuration on any port channels, or interfaces, or do you meant that the "master" takes the config of the "slave" and adds it to the config. My understanding is really it's an interface name change as far as the interface configs are concerned correct? All of the individual interfaces and port channels (as long as the port channels are all numbered differently) keep their config, though it now is controlled by the "master". But as far as HSRP, I would have to change the IP address to the VLANs to the current virtual IP, and remove the HSRP config correct?

[educruz]

Good day,

In a Virtual Switching System (VSS), the two Catalyst switches (e.g. CORE-1 and CORE-2), will act as one "single" logical switch, although physically speaking, there are still two switches. 

We can think of this like the "stacking" feature of the Cat3750 or Cat3850 switches. Although there are many physical switches, they are seen by other systems logically speaking as one stack. 

The switches that are part of the VSS, are synchronized via something call VSL link, which is usually a Port-channel between these switches. This is something similar to the stacking cables of the other platforms, if that makes sense. 

Once this VSS system is configured, up and running, your downstream switches or end hosts will believe that this is a single system rather than two different switches (in terms of STP, Etherchannel, Routing Protocols, etc.). 

As a consequence, this eliminates the need of HSRP at all, or any other configuration existing in "CORE-2". My understanding is that only the port configuration in "CORE-2" is retained after creating a VSS system, but when merging two switches in a VSS system it would be preferable to do it under a maintenance window. 

Lastly, there are a few pre-requirements of software and hardware before creating a VSS system. You may want to take a look at these links for further information:

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst4500/15-1-2/XE_340/configuration/guide/config/vss.html

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst6500/ios/12-2SX/configuration/guide/book/vss.html

Hope this helps.

Eduardo.

[LandrinLong]

Yes, I've read all of the documentation, and understand it.  My question had to do with how the conversion from standalone to VSS handles the configuration of HSRP.  In our particular instance we use HSRP on our VLANs.  Each switch has it's own IP address x.x.x.249 on Switch 1, and x.x.x.254 on Switch 2.  The HSRP virtual IP address is x.x.x.250.  All of the hosts for each VLAN are setup to use x.x.x.250 as their default gateway.  My question was, when the conversion to VSS happens, how does it convert the HSRP configuration?  Will the virtual IP address still be there, there will just be no HSRP neighbor, which will then allow me to remove the HSRP configuration and remove the x.x.x.249 and x.x.x.254 IP addresses and just address the VLANs like a normal VLAN with the x.x.x.250 address?  Since I cannot find any good information on it, nor can I setup VSS in a virtual or simulated environment, I felt I should ask here.

[educruz · Accepted solution]

Understood, that is a very good question. 

Let's assume your current "CORE-1" already has some SVI (e.g. VLAN125) configured with a physical IP address, and with an HSRP virtual IP address too. When both switches are converted to VSS, the HSRP configuration is retained by the Active switch (in most of the cases that would be "CORE-1").

"CORE-2" will become a Standby switch within the VSS system, so whatever configuration it had before being VSS, will be overwritten by the configuration of "CORE-1". Ultimately there will only be one system, let's name it "VSS-1".

Once VSS-1 is up, when the HSRP process starts, it will listen to see if there is any other peer. There will be none, so VSS-1 will declare itself as Active for HSRP, and your end hosts should not be affected because the virtual IP for the default gateway, will still be under the SVI configuration that was retained by "CORE-1". You would just not have a backup HSRP switch anymore. 

Hope this helps.

Eduardo.

[LandrinLong]

Perfect.  Thank all of you for providing me with the info.  I think I'm armed with everything I need now.  Next step...prep work and cabling with a scheduled down time.  I can't wait!

[stuartcross]

Did you get an answer on this at all? I have the same question.  If the HSRP config is kept the same and it can find no HSRP peer, it will go active and forward traffic. But that seems messy, and keeps unnecessary config and HSRP traffic.  I'm going to assume you will just gave to re-write the config after the conversion, i.e, remove the HSRP config from the SVI and re-address the SVI Ip address to be the old HSRP virtual IP?