Routing Inter-vlan Using Etherchannel 3

[taonrez]

Hello, Team,

I want to connect the PCs in VLAN 10 to the PCs in VLAN 40 through two Layer 3 switches on which I have configured EtherChannel 3. But the communication fails.
Please find the architecture in the attached image (at the bottom of the page). And the main configurations of the two switches are below.
Can someone please help me resolve this issue?

SW1:

SW1#show running-config

hostname SW1
!
ip routing
!
spanning-tree mode pvst
!
interface Port-channel1
no switchport
ip address 10.1.50.1 255.255.255.0
!
interface FastEthernet0/1
switchport access vlan 10
switchport mode access
!
interface FastEthernet0/2
switchport access vlan 20
switchport mode access
!
interface GigabitEthernet0/1
no switchport
no ip address
channel-group 1 mode on
duplex auto
speed auto
!
interface GigabitEthernet0/2
no switchport
no ip address
channel-group 1 mode on
duplex auto
speed auto
!
interface Vlan1
no ip address
shutdown
!
interface Vlan10
mac-address 000a.f313.ea01
ip address 10.1.10.1 255.255.255.0
!
interface Vlan20
mac-address 000a.f313.ea02
ip address 10.1.20.1 255.255.255.0
!

SW2:
SW2#show running-config
!
hostname SW2
!
ip routing
!
interface Port-channel2
no switchport
ip address 10.1.50.2 255.255.255.0
!
interface FastEthernet0/1
switchport access vlan 30
switchport mode access
!
interface FastEthernet0/2
switchport access vlan 40
switchport mode access
!
interface GigabitEthernet0/1
no switchport
no ip address
channel-group 2 mode on
duplex auto
speed auto
!
interface GigabitEthernet0/2
no switchport
no ip address
channel-group 2 mode on
duplex auto
speed auto
!
interface Vlan1
no ip address
shutdown
!
interface Vlan30
mac-address 0001.971e.d501
ip address 10.1.30.1 255.255.255.0
!
interface Vlan40
mac-address 0001.971e.d502
ip address 10.1.40.1 255.255.255.0
!

[MHM Cisco World]

You need static route config in both L3SW for each vlan connect to that SW

MHM

[Enes Simnica · Accepted solution]

hello @taonrez  Based on what you've posted, the core issue seems to be missing routing between VLANs across the switches. You’ve created Layer 3 EtherChannels (po1 and po2) with IPs on both ends, but there’s no routing between VLAN 10 (SW1) and VLAN 40 (SW2).

Here’s what u need to do:

1. Add static routes or use a dynamic routing protocol (like OSPF or EIGRP) so the switches know how to reach each other's VLANs via the Port-Channels.

For example, on SW1:

ip route 10.1.40.0 255.255.255.0 10.1.50.2
And on SW2:

ip route 10.1.10.0 255.255.255.0 10.1.50.1

• Make sure the PCs have correct default gateways — for VLAN 10, it should be 10.1.10.1; for VLAN 40, it should be 10.1.40.1.

• Test with a ping from one switch to the other using VLAN SVI IPs  to confirm routing is working.

If that doesn’t solve it, paste here ur topology as ZIP and ill fix it for u....

-Enes

[paul driver · Accepted solution]

Hello
Static routing is to administrative in the long term, suggest an IGP would be applicable

SW1
ip routing
router ospf 1
router-id 10.1.50.1
passive interface default
no passive interface port-channel 1

interface Port-channel 1
ip ospf 1 area 0
ip ossf network point-to-point

int range vlan 10, 20
ip ospf  1 area 1


SW2
ip routing
router ospf 1
router-id 10.1.50.2
passive interface default
no passive interface port-channel 2

interface Port-channel2
ip ospf 1 area 0
ip ospf network point-to-point

int range vlan 30, 40
ip ospf  1 area 2

[Joseph W. Doherty · Accepted solution]

Both @MHM Cisco World and @Enes Simnica have correctly identified the issue, i.e. neither switch has routes for networks not directly connected to the switches.  The Etherchannel, isn't the problem, a single link would have the same issue.

To be clear, in the example static route statements that @Enes Simnica provides, he's only showing one static route, per switch, but that kind of static routes would need one for each remote network, or a summary/aggregate route for multiple remote networks.

For example, SW1 would need:

ip route 10.1.30.0 255.255.255.0 10.1.50.2
ip route 10.1.40.0 255.255.255.0 10.1.50.2

To use summary/aggregate routes, you would need to have considered that in what address blocks you use, and where you use them.

For example if SW1 had 10.1.2.0/24 and 10.1.3.0/24, they could have been summarized using 10.1.2.0/23.  For just two /24s it matters little, but understanding summary/aggregate routes, and how to take advantage on them, is useful to know.

In this particular case, you can use a single global default route, on each switch, although that would work correctly for the actual networks, a non-existent network, like ping 10.1.50.1, would cause a routing loop.

BTW, if using something like Packet Tracer, be aware it doesn't usually (if ever) support all features, and the features it does support, don't always work as they should.

Further, if you were doing this for "real", likely you would use LACP, use a /30 or /31 for the Etherchannel, concern yourself with the Etherchannel load balancing choice, etc.

[M02@rt37]

Hello @taonrez 

First, you must add static routes (or a dynamic routing protocol) on both switches to allow L3 routing between VLANs across the L3 Etherchanel.

Give you some tips to troubleshoot by yourself next time:

Ensure PC default Gateways match the correct SVI IPs.

Verify that SVIs are all up with command show ip interface brief and that Port-channels are up too: show etherchannel summary.

Check IP table with show ip route command -- You could also use a routing protocol like OSPF or EIGRP between SW1 and SW2 for automatic route learning if your design grows...

A lot of PT ressources exist on internet to help you as concerned basic config of routing protocol.

[taonrez]

Hi,
Thank you all for your various suggestions.
I've defined the static routes as you recommended, and it's currently working fine.
But I have a question that comes to mind:
How can we explain the fact that frames destined for different VLANs can travel over the Etherchannel link, yet there is no trunk defined between the two switches???

[Joseph W. Doherty · Accepted solution]

---

@taonrez wrote:

How can we explain the fact that frames destined for different VLANs can travel over the Etherchannel link, yet there is no trunk defined between the two switches???

---

Because the Etherchannel is NOT passing L2, it's passing L3.  I.e. the port-channel interfaces are L3.

[Joseph W. Doherty]

Oh, BTW, if the Etherchannel between the two switches was a L2 trunk, you wouldn't, in this case, need any additional routing configuration.  You could also have the four SVIs configured however you like on the two switches.  I.e. logically it wouldn't matter which switch has the actual SVI.

Additionally, you could have all SVIs configured on both switches, although they would need different IPs, however if using a FHRP (e.g. HSRP) you could have a virtual IP shared between the switches.

I only mentioned the foregoing because I suspect you're learning more about networking and how much is configured depends on multiple factors.  I'm guessing L2 and L3 can be a bit confusing on a L3 switch because it's also a L2 switch.

In ye olden tymes, L2 (w/o switches or VLANs) and L3 were, possibly, a bit easier to understand, but, laugh, there were things we had to understand that are pretty much non-existent today; not all, though.  ; )

[Martin L]

note that PT is just  a sim and maybe not ideal for this advanced tech setup; have u tried Free CML version? 

Regards, ML
**Have fun labbing!!!***
***Please Rate All Helpful Responses ***

[taonrez]

No. I don't try it.

I'll take a look

[Joseph W. Doherty]

---

@taonrez wrote:

No. I don't try it.

I'll take a look

---

BTW, just so you'll know, CML is much, much more resource intensive on your PC.  Whatever features its devices support, often tend to be whatever a similar physical device would provide, and usually all configuration options are there.

The personal CML version I have, for L3 switches, I recall, only provides virtual versions of the Catalyst 9Ks, but each is such a resource monster, my 16 GB PC doesn't have enough RAM to spin up even one of them.