How to test layer 2 connectivity on Cisco Switch?

Question

I'm testing a new FTTH CPE in our lab. A Cisco ME3400 switch. So far I'm having issues in provisioning them. I have activated DHCP debugging to see the DHCP packets.

I wonder how can I test to know if there is layer 2 connectivity between the CPE and ME3400?

Some output :

ME3400#sh int fa0/1 FastEthernet0/1 is up, line protocol is up (connected) Hardware is Fast Ethernet, address is 0023.05ab.c883 (bia 0023.05ab.c883)

ME3400#sh mac address-table

Vlan Mac Address Type Ports
---- ----------- -------- -----
All 0100.0ccc.cccc STATIC CPU
...
1 XXXX.XX29.c942 DYNAMIC Gi0/1
1 XXXX.XXe4.0bdd DYNAMIC Gi0/1
1 XXXX.XX70.113e DYNAMIC Gi0/1
10 XXXX.XXa1.4ca0 DYNAMIC Fa0/1

score 11 · Accepted Answer · answered May 28 '13 at 08:29

11

If you see MAC address is 'mac address-table' you have L2 connectivity. So nothing wrong in your test methodology.

answered May 28 '13 at 08:29

ytti

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score 2 · Answer 2 · edited May 28 '13 at 19:58

2

you may want to try a Layer2Traceroute:

Router# traceroute mac [interface type interface_number] source_mac_address [interface type interface_number] destination_mac_address [vlan vlan_id] [detail]

Once you have confirmed L2 connectivity, can you explain the problem with the provisioning in more detail please?

edited May 28 '13 at 19:58

Mike Pennington

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answered May 28 '13 at 08:35

Max

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AFAIK it relies on CDP, and I doubt his FTTH CPE is Cisco or CDP enabled. – ytti May 28 '13 at 08:36
Thanks for the tips. Here some details on traceroute layer 2 link
Because I'm testing remotely the CPE's, I've more issues on test. I ask to reboot the modems and them start to "Discover" DHCP.

Now I've some issue on provisioning. I've configured the DHCP server on Switch, obsviously only for straighforward test of CPE. And I get this issue :

DHCPD: client rejected 172.16.245.103, sent 172.16.245.132.

Have any idea ? All this, is for evaluate the CPE's
– cgasp May 28 '13 at 10:16

score 2 · Answer 3 · answered May 28 '13 at 12:31

You can check the mac address table, but there won't be an entry unless there's been traffic. A quick method I often use is to ping the device (assuming it has an IP). Even if it doesn't respond to ping it should respond to ARP, and there will be an entry in the ARP table for that IP.

score 0 · Answer 4 · answered Sep 12 '16 at 16:31

0

Q. how can I test to know if there is layer 2 connectivity

A. Configure LLDP and/or show interface

answered Sep 12 '16 at 16:31

Ronnie Royston

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score -1 · Answer 5 · edited Sep 13 '16 at 12:23

-1

#show mac address-table

This will show stored MAC addresses in the switch mac address table, these could be statically assigned by the administrator or user. Or they may be dynamically learned by passing traffic through interfaces.

edited Sep 13 '16 at 12:23

Ron Maupin

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answered Sep 12 '16 at 05:58

Ty Smith

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hey hey now....Helping someone see they were mistaken...one thing were all on the path of learning to be better engineers. down voting. Thats kind of bold unnecessary =) just saying...... – Ty Smith Sep 13 '16 at 03:32

How to test layer 2 connectivity on Cisco Switch?

5 Answers5