Network Links

[ryno7819]

I need the ability to manage Network B from Network A.  Currently we have a physical link between the two switches and things are working fine. But Switch 1 in Network B is going away and it's an HP switch. It is being replaced by a Cisco switch.  What would the port config look like on each end? Both switches are layer 2. And I want to make dang sure no routing gets affected on either network when I create this new link.  Currently on Switch 2 of Network A, the port config looks like this: 

interface GigabitEthernet1/0/48

switchport access vlan 231

switchport mode access

spanning-tree portfast (remove this?)

The port config on the HP switch that is being removed looks like this:

vlan 4
name "Network A"
untagged 38
tagged A1
no ip address
exit

So as you can see I have VLAN 4 on one end and VLAN 231 on the other but it's been working this way for years. 

Anyways, what would the config look like on the new Cisco switch? Wouldn't I use the same config above? Something similar to this?

interface GigabitEthernet3/0/31

switchport access vlan 231

switchport mode access

spanning-tree portfast (remove this?)

[balaji.bandi]

If you like to allow only allow VLAN respected and that should work as expected.

In most cases switch to switch I personally configure as trunk so you can enable later whatever VLAN required in the future with no downtime.

Converting from Access to trunk required some downtime (if this is an opportunity take advantage) - but if the requirement only and no future VLAN required above should work.

If you do not like the new switch to become a root bridge due to the spanning tree process, then check the priority on the running one, make sure it is higher in the new switch.

[Martin L]

You can copy config from 1/0/48 to new port on new Cisco switch and keep portfast.   But this config tell us that port is access mode (switchport access) connecting end device like PC. And ports used to connecting to other switches are in in module and numbering looks like  1/1/1 thru 1/1/4

Usually, 2 switches should be configured with switchport mode trunk command to established trunking vlans between 2 switches.  Using access vlan x between 2 switches on trunk link means only that vlan x traffic is allowed, no other vlans which is not what trunk link should do (not purpose or goal of trunks).

so, configs for a link connecting 2 switches should be trunking and look like this:

interface x/z/y

switchport trunk encap dot1q

switchport mode trunk

Regards, ML
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[paul driver]

Hello

---

@ryno7819 wrote:

interface GigabitEthernet1/0/48

switchport access vlan 231

switchport mode access

spanning-tree portfast (remove this?)

vlan 4
name "Network A"
untagged 38
tagged A1
no ip address
exit

---

You sure this indeed working this like as the above isn’t applicable for either port A1 or port 38 to be able connect?

Going forward the cisco port configuration you suggest is applicable, but it will mean the new cisco switch will only be able to support vlan 231 for all it ports, if that is what you require then all good.

If you have bpduguard enable globally on the current cisco switch and the new switch you may need to turn that off globally and append it to be interface specific or apply bpdu-filter on the cisco ports connecting to each other.

[ryno7819]

Well I don't know much about HP configs and I do see A1 in the VLAN 4 on the HP switch so maybe you're onto something:

vlan 4
name "LACC-FAC"
untagged 38
tagged A1
no ip address
exit

So it sounds like each port on each switch A and B should look like this?

interface x/z/y

switchport trunk encap dot1q

switchport mode trunk

I guess my concern (and maybe it is not a concern but I don't know what I don't know, ) Is that by connecting Switch A on Network 1 to Switch B on Network 2, will any sort of routing get mucked up since I have two seperate networks now connected to each other and each network of course has it's own L3 router?  (the two switches i am connecting are only L2).  No concern or any special thing I need to do to make sure routing doesn't change?

Thanks everyone for the help.

[paul driver]

Hello

---

@ryno7819 wrote:
(the two switches i am connecting are only L2). No concern or any special thing I need to do to make sure routing doesn't change?

---

It does seem those two switches are presently physically connected but are not logically connected.
Now  if you wish to connect them together just to only manage both networks then it possible an access port between those two switches would be applicable.

Can you post a topology diagram of your network in relation to these two switches and confirm exactly the nature of this connection?

[ryno7819]

Yes, this link is for mgmt purposes only.  But currently it does look like it must be using a trunk port because on the HP side (Network B) it is VLAN 4 on the L2 switch and also on the router. The router has no reference to VLAN 231.  Whereas on Network A, the router and switch has VLAN 231 in it's config but not VLAN 4. And everything works.  These two L2 switches in the diagram below will be physically connected via copper cable. May not get a chance to reply again until later.  Really appreciate the help here!

[ryno7819]

Hello - Does the topology help any in determining how I should have my port configs on each end? 

[balaji.bandi]

As suggested always go cisco switch to switch trunk for your requirement.

until you have any concerns ?

[ryno7819]

But I don't need to be concerned with routing issues between the two networks if I am connecting two differnet networks L2 switches together where each network as it's own L3 router? The port config on each end would look like this?

interface x/z/y

switchport trunk encap dot1q

switchport mode trunk

[balaji.bandi]

yes that shoul work,

another question, if they working their own Layer3, do they need to communcate each other ?

then you may need some routing ?

[ryno7819]

 I believe the routing is already in place since these two networks have a link currently with the HP / Cisco switch mentioned above. 

[balaji.bandi]

then you are bridging with only Layer 2, i think you good to go, any issue reported back.

[ryno7819]

Ok, so that's how it works? If L2 connects to another L2, there should be no concern of routing issues? Thx for the info.

[balaji.bandi]

if this just Layer 2 i do not see any issue, test and advise