Switching from DS3 to Switched Ethernet Circuit

[aagarwalcca]

Hi Everyone, 

I am trying to switch from a DS3 circuit to a switched ethernet circuit. We have 2 campuses both with a 3845 router which has a DS3 modules on it. We recently purchased a switched ethernet circuit provided by AT&T. I thought I could just use one of the available ports on each router, give it an IP address in same subnet and it will communicate. Just like a serial port. But it do not work this way.

I am not very clear on what a switched ethernet circuit is and what all I need to make this work. Any help will be really appreciated. 

Thank you, 

Ankit

[Jon Marshall]

If the circuit is just meant to be L2 and not L3 then what you did is exactly what you should be able to do.

When you did this setup did both interfaces shows as up/up and did you just try pinging between the IPs ?

If so what did the arp table on each router show ?

Jon

[aagarwalcca]

Hi Jon, 

I did not check the arp table. However it was up/up on both side and AT&T could also see the circuits up on their side too. I wasn't able to ping any side.

Ankit

[Joseph W. Doherty]

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Posting

Ethernet hand-offs can connect to various technologies.

Your Ethernet connections might require VLAN tags.

You should know all the specifics about your WAN Ethernet connections.  If you don't you should be able to obtain that information from your service provider.

Besides Jon's suggestion of looking at the ARP table, does CDP show the other side's device?

[aagarwalcca]

Hi Joseph, 

I think it requires VLAN tags. But I use 3800 router where I cannot put the vlan tag. 

-Ankit

[Jon Marshall]

Ankit

Do you know the vlan you should use ?

If so you should be able to use a subinterface on each router.

Jon

[aagarwalcca]

Yes I have to use vlan 1000. I tried tagging like this but this didnt work:

interface GigabitEthernet0/0

description TO SF-MDF

ip address 10.8.6.1 255.255.255.252

shutdown

duplex full

speed 1000

media-type rj45

vlan-id dot1q 1000

  exit-vlan-config

[Jon Marshall · Accepted solution]

I was thinking you should use a subinterface, so remove the IP address from the main interface and -

int gi0/0.x   <--  see below for "x"
encapsulation dot1q <vlan ID>
ip address 10.8.6.1 255.255.255.252
etc.

note you usually make the subinterface number the same as the vlan ID but not sure if it will take that number.

You can try it but it doesn't really matter what number you give the subinterface because it doesn't have to match the vlan ID, it is the encapsulation command that needs to reference the actual vlan ID.

Jon

[aagarwalcca]

Hi Jon, 

Thanks a lot. let me try to do this tonight and see if it works. 

-Ankit