topic You should not see an arp in Switching

Layer 3 Switch act as Layer 2 switch

Caitlyn Sims — Fri, 08 Mar 2019 18:50:40 GMT

Hi,

I have a question regarding my layer 3 switch. Currently, the network works fine except that the layer 3 switch (which is Curly) cannot ping outside the management VLAN, and other devices cannot ping it. Moe can ping all devices fine.

So, my question is, how do I get Curly to ping the PC's and other router interfaces. I have not had much experience with the 3560 switch. Any help would be greatly appreciated

Thanks

Cannot read your attachment

Jon Marshall — Sun, 04 Jun 2017 10:10:33 GMT

Cannot read your attachment but at a guess if the L3 switch is not routing and has just a L3 vlan interface for management then you need to add -

"ip default-gateway x.x.x.x"

where x.x.x.x is the L3 interface on another of your devices that is responsible for routing the management vlan.

Jon

Hi Jon,

Caitlyn Sims — Sun, 04 Jun 2017 12:02:27 GMT

Hi Jon,

Sorry about the attachment, wouldn't let me upload just the packet tracer file and had to zip it up.

The L3 switch already has a default gateway, that of the IP address of the router sub interface of the management vlan.

VLAN 452 is the management VLAN, and in the picture the default gateway for the switch is the same as the sub interface on the router.

I actually meant not all of

Jon Marshall — Sun, 04 Jun 2017 12:03:06 GMT

I actually meant not all of us have access to the software you are using so best to attach configurations and a diagram.

It sounds like it is setup correctly with it's default gateway.

Assuming the L3 switch only has one SVI ("int vlan x") and that is the management vlan and assuming that the trunk connection is allowing the vlan then can you make sure IP routing is not enabled on the switch otherwise it will ignore the default gateway setting.

If that makes no difference attach configurations and diagram.

Jon

Ok, sorry, I'm very new to

Caitlyn Sims — Sun, 04 Jun 2017 12:07:42 GMT

Ok, sorry, I'm very new to this forum.

I have attached the device configs for Larry (the router) and Curly (the L3 switch), and also the diagram

No need to apologise :)

Jon Marshall — Sun, 04 Jun 2017 12:38:31 GMT

No need to apologise 🙂

Okay, your configurations look good at the moment.

So from the switch can you ping 83.174.64.206 ?

Can you also post from the switch the following -

"sh int trunk"
"sh ip route"
"sh vlan"

Jon

Yes, the switch can ping 83

Caitlyn Sims — Sun, 04 Jun 2017 19:06:22 GMT

Yes, the switch can ping 83.174.64.206 and ....204 (which is Moe).

Ok, sorry, I'm very new to

Dan Lukes — Sun, 04 Jun 2017 19:07:09 GMT

Ok, sorry, I'm very new to this forum.

No problem, but you may be interested to know the communities of CSC are related to support of real hardware. As you mentioned Packet Tracer I assume the we are speaking about Packet Tracer simulated network. Packet Tracer is in Cisco Learning courses tool thus it's better to ask in appropriate community of Cisco Learning Network next time.

Cheers

Dan

Again it all looks fine.

Jon Marshall — Sun, 04 Jun 2017 19:27:21 GMT

Again it all looks fine.

Just to clarify do all devices use the router as their default gateway IP in the respective vlans ?

Jon

Yes. While I was testing

Caitlyn Sims — Sun, 04 Jun 2017 19:32:36 GMT

Yes. While I was testing yesterday I checked and both the pcs can ping each other, and moe can ping every sub interface of the router, but curly can only ping the vlan.

So from the L3 switch you

Jon Marshall — Sun, 04 Jun 2017 19:44:46 GMT

Sorry you did say you couldn

Jon Marshall — Sun, 04 Jun 2017 19:46:06 GMT

Sorry you did say you couldn't ping any other router interface IPs.

When you try what does the arp table on the L3 switch look like ?

Also can you post a "sh spanning-tree vlan 452" from the switch.

Jon

Just checked that output

Jon Marshall — Sun, 04 Jun 2017 19:56:15 GMT

Just checked that output again and with the "sh int trunk" it is saying that on both trunks there are no vlans in STP forwarding state which is obviously not how it should be.

But then this would mean nothing was being forwarded and yet you can ping within the network.

Not sure what is going on at the moment.

Jon

Yes, that's correct. L3

Caitlyn Sims — Sun, 04 Jun 2017 20:04:19 GMT

Yes, that's correct. L3 switch cannot ping outside of the management VLAN.

Here is the spanning tree vlan 452

Curly#sh span vla 452

VLAN0452

Spanning tree enabled protocol ieee

Root ID Priority 25028

Address 00E0.F774.E59E

This bridge is the root

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 25028 (priority 24576 sys-id-ext 452)

Address 00E0.F774.E59E

Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Aging Time 20

Interface Role Sts Cost Prio.Nbr Type

---------------- ---- --- --------- -------- --------------------------------

Fa0/11 Desg FWD 19 128.11 P2p

Po1 Desg FWD 9 128.27 Shr

F0/11 is the connection to the router and Po1 is an EtherChannel link to Moe, the L2 switch

And the arp table after

Caitlyn Sims — Sun, 04 Jun 2017 20:07:08 GMT

And the arp table after trying to ping 83.174.64.190

Curly>sh ip arp

Protocol Address Age (min) Hardware Addr Type Interface

Internet 83.174.64.190 0 0001.6499.8402 ARPA Vlan452

Internet 83.174.64.205 - 00E0.F774.E59E ARPA Vlan452

You should not see an arp

Jon Marshall — Sun, 04 Jun 2017 20:24:02 GMT

You should not see an arp entry for 83.174.64.190 because, unless I have got my maths wrong, it is in a different IP subnet.

The only arp entries you should see would be for devices in the same vlan/IP subnet as the L3 switch.

It looks like the switch still thinks it should be L3.

This should not make a difference but can you on the switch administratively shutdown all the other vlan interfaces except the management one obviously.

Jon

Hi Jon,

Caitlyn Sims — Sun, 04 Jun 2017 20:45:17 GMT

Hi Jon,

This is what appears as it is freshly opened, with the other vlans shutdown.

Curly>sh ip arp

Protocol Address Age (min) Hardware Addr Type Interface

Internet 83.174.64.205 - 00E0.F774.E59E ARPA Vlan452

And yes, 83.174.64.190 is in a different vlan, the final usable address in the vlan before I believe.

If you now ping 83.174.64.190

Jon Marshall — Sun, 04 Jun 2017 20:50:43 GMT

If you now ping 83.174.64.190 what you should then see in the arp table is an entry for 83.174.64.206 ie. the default gateway for the management vlan.

Can you try that and post results.

Jon

Curly>sh ip arp

Caitlyn Sims — Sun, 04 Jun 2017 21:01:46 GMT

Curly>sh ip arp

Protocol Address Age (min) Hardware Addr Type Interface

Internet 83.174.64.190 0 0001.6499.8402 ARPA Vlan452

Internet 83.174.64.205 - 00E0.F774.E59E ARPA Vlan452

This is what I got. Don't seem to be getting the 83.174.64.206 which is what I should be getting.

There is definitely something

Jon Marshall — Sun, 04 Jun 2017 21:11:21 GMT

There is definitely something not working properly.

It may be a software bug, difficult to say but you should only see arp entries for devices in multiple vlans when the switch is acting a L3 switch.

Have you tracked down those mac addresses ie. what devices are they ?

Jon