Bridging Over a Wide Area Network using dte dce cable

[ts015]

Hi All,

I have 2 Cisco routers connected via DTE-DCE cable for simulating T1 connection but both serial ports do not seem to be working. Could someone please help check my configuration below. I am trying to ping computer B at the Ethernet port of router B from computer A at the Ethernet port of router A.

Router A as DCE	Router B as DTE
interface fastethernet0/0	interface fastethernet0/0
ip address 192.168.1.100 255.255.255.0	ip address 192.168.1.200 255.255.255.0
no shutdown	no shutdown
bridge-group 1	bridge-group 1
exit	exit
interface serial 0/0/0	interface serial 0/0/0
ip address 128.0.1.10 255.255.255.0	ip address 128.0.1.20 255.255.255.0
clock rate 64000	no shutdown
bandwidth 64	bridge-group 1
no shutdown	bridge 1 protocol ieee
bridge-group 1	exit
bridge 1 protocol ieee
exit

Also, both serial ports on router A and B are down in the status, I think I may have missed something to bring it up.

If DTE-DCE cable is replaced by T1, do I still need to put clock rate and bandwidth on router A?

Thank you very much.

[Peter Marshall]

This article covers the topic fundamentals:

https://learningnetwork.cisco.com/thread/20426

As for this, question, "If DTE-DCE cable is replaced by T1, do I still need to put clock rate and bandwidth on router A?"

If you have T1 cards, you'll need a T1 crossover cable. This article seems to cover the T1 conversation:

https://community.cisco.com/t5/routing/4-port-hwic-t1-e1-and-multilink-config-for-2911-router/td-p/2055480?dtid=osscdc000283

[Alan Ng'ethe]

A different way of bridging that has worked for me in the past is to bridge the Ethernet traffic over a GRE tunnel. Rather than have IP addresses on the LAN interfaces, we just have them as part of bridge group 1.
I have used a tunnel with mode gre ip with successful results. In your case this would look something like the below;

Router A as DCE

interface fastethernet0/0

no ip address

no shutdown

bridge-group 1

bridge-group 1 spanning-disabled

exit

interface serial 0/0/0

ip address 128.0.1.10 255.255.255.0

clock rate 64000

bandwidth 64

no shutdown

exit

interface Tunnel0

description GRE tunnel to RTR B

no ip address

tunnel source serial 0/0/0

tunnel destination 128.0.1.20

bridge-group 1

bridge-group 1 spanning-disabled

Below commands in global configuration

bridge 1 protocol ieee

bridge irb

The router B config would be a mirror of router A config. Perhaps that is worth a try to see whether the line protocol will come up on the serial interfaces.

Also, there's a gotcha. when you add the bridge-group 1 and bridge-group 1 spanning-disabled commands to the tunnel you may receive a warning '% This command is an unreleased and unsupported feature', but it will still work.

[ts015]

Hi Alan Ng'ethe,

Thanks for your help. The serial port shows down in status after following your configuration, any other clue?

Thank you.

[Alan Ng'ethe]

Hi @ts015,

Have you confirmed which end of the cable is the DCE and DTE by running show controllers serial 0/0/0 to see which router has the DTE or DCE end of the cable attached? Can you do so (again) and paste the output here?

Please also include the output of show ip interface brief

This appears to be a physical layer issue.

Thanks.

[ts015]

Hi Alan Ng'ethe,

Yes, I just found out that my cable had some problems. Everything works after changing the cable.....

However, do you know if clock rate is required when T1 connection is deployed.

Thank you very much.

[Alan Ng'ethe]

Hi @ts015,

This article by Cisco doesn't seem to suggest so as the clock rate command isn't among the required tasks;

https://www.cisco.com/c/dam/en/us/td/docs/routers/ncs4200/configuration/guide/tdm/16-8-1/b-tdm-t1-e1-xe-16-8-1-ncs4200.html#con_1072390

You can also use the hyperlink provided in the earlier responses for more examples.

Remember to rate any posts that have been helpful.

[ts015]

Hi Alan Ng'ethe,

Do you know what else do I need to configure the routers so that I can ping the Ethernet port in switch B from computer A?

Computer A: 192.168.1.101
Ethernet@router A: 192.168.1.100
Serial@router A: 128.0.1.10
Serial@router B: 128.0.1.20
Ethernet@router B: 192.168.1.200
Computer B: 192.168.1.201

I can now ping the computer B from computer A but not able to ping 192.168.1.200 from 192.168.1.101. Could you please help?

Thank you.

[Alan Ng'ethe]

 Hi @ts015,

Could you upload the all configurations from both routers? Save to text files, then upload here.

Thanks

[ts015]

Hi Alan Ng'ethe,

OK, let me upload it here.

[Alan Ng'ethe]

Hi @ts015,

Thanks for the configuration. After simulating this I was not able to make the router LAN interfaces ping each other, and neither could either PC ping the LAN interface of the remote router. I do not have an idea why this is the case at this point, but I do encourage you to read through the following articles and see whether you may be able to arrive at a reason why this does not work.

https://community.cisco.com/t5/switching/explanation-about-bridge-group/td-p/772614

https://community.cisco.com/t5/switching/bridge-mode-over-t1-even-possible/td-p/1259289

https://www.cisco.com/c/en/us/support/docs/ibm-technologies/source-route-transparent-srt-bridging/10676-37.html#ex7

And as mentioned by veteran Richard Burts and others, while it is certainly POSSIBLE to configure bridging to link 2 LANs over a serial link, it is generally not advised to do so.