Layer-2 switching issue between two different switches.

[ajeet-gupta]

We have a network setup where a Hirschmann switch is connected to a Cisco Catalyst 9300 operating in Layer 2 mode. Currently, we do not have administrative access to the Hirschmann switch, so its configuration cannot be verified.

As per the existing design, the link between the Cisco Catalyst 9300 and the Hirschmann switch allows native VLAN 1, and all connected switches/end-hosts are reachable without any issues.

Now, as per the customer’s requirement, we are planning to:

• Move the management SVI to the firewall
• Change the management VLAN from VLAN 1 to VLAN 2110

However, after implementing this change, the Hirschmann switch becomes unreachable.

We need guidance on what configuration changes should be made on the Cisco Catalyst 9300 so that, along with VLAN 2110, reachability to the Hirschmann switch is maintained.

[Mark Elsen]

 - @ajeet-gupta  You can't resolve this without coordinated configuring and testing on both platforms. If that is currenrly not possibleb, then you need to revert on the cisco switch ,

 M.

[M02@rt37]

Hello @ajeet-gupta 

Hirschman switch is still using untagged/native vlan1 for management... and since you don’t have access to change it, moving management to vlan 2110 breaks connectivity.

On your c9300, you should keep vlan 1 as the native vlan and simply allow vlan 2110 on the trunk, so both vlan coexist; otherwise, without reconfiguring the Hirschmann side to tag vlan 2110, it will remain unreachable...

[Joseph W. Doherty]

Move the management SVI to the firewall

Unclear what that means.  You can "move" a gateway from one device to another or you can change a device's management IP.

Change the management VLAN from VLAN 1 to VLAN 2110

Is the management addressing being changed?

[ajeet-gupta]

Hello Joseph,

Moving management VLAN, I mean that currently the IP address for MGMT is configured under VLAN-1 and same VLAN is native VLAN.
Now customer wants to use the same IP addressing for MGMT but under VLAN 2110 and insisting to use 2110 VLAN as native VLAN.

[Joseph W. Doherty]

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@ajeet-gupta wrote:

Hello Joseph,

Moving management VLAN, I mean that currently the IP address for MGMT is configured under VLAN-1 and same VLAN is native VLAN.
Now customer wants to use the same IP addressing for MGMT but under VLAN 2110 and insisting to use 2110 VLAN as native VLAN.

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Maybe, it might be as simple as defining V2110 as native on trunk links, and changing your L2 switch's management SVI to V2110.  You might, though, if you have a default-gateway defined, need to migrate and/or change it too.

[Giuseppe Larosa]

Hello @ajeet-gupta ,

the move from VLAN 1 to VLAN 2110 also includes a change in IP subnet or the IP subnet stays the same ?

In this second case there is no way to recover the Hirschmann switch and you should rollback to previuos configuration (unless who manages this switch can access it in a console port and  make the required changes)

If the change of management VLAN includes also the use of a different IP subnet the catalyst 9300 can become the new default gateway in vlan 1 for the affected switch but Cat9300 SVI vlan1 IP address has to become the one used before as defaut gateway.

Hope to help

Giuseppe

[ajeet-gupta]

Hello Larosa,

I have to use same IP addressing.

[Dustin Anderson]

ok, assuming you are keeping the IP scheme and just changing the vlan, you should be able to make it work by just making the port on the Cisco and access port on the vlan 2110. If the link is L2 untagged, then the vlan doesn't matter as each switch will treat the traffic as it's native vlan. If the other switch lets the Cisco switch know it's vlan, you could get a vlan mismatch error on the Cisco switch and may want to look at some filtering BPDU etc.