Newbie - Configuration question. Is this possible?

derrick · ‎10-30-2002

Our company is expanding to two locations about 4 miles apart. (I have just inherited this position and I need some advice.)

The previous Admin had ordered a Qwest T1 Circut and was planning on using the same network on both ends of the connection. Please see diagram below.

(192.168.0.x) E0 --> Cisco 1721 --> S0 ---> Qwest T1 Circut ---> S0 --> Cisco 1721 --> E0 (192.168.0.x)

The Qwest T1 / S0 line is configured for ESF, b8zs, PPP.

My question is this. Is it possible to have the same network address on both ends (The E0 circuts)? If so, do I need to enable NAT? Both ends will have about 10 users.

Currently when I use the Cisco ConfigMaker, it tells me that the E0 interfaces need to have different networks.

Any help would be appreciated.

-D

rsissons · ‎10-30-2002

The only way you can have the same network at both ends is by disabling IP routing, 'no ip routing', on both the routers and bridging the traffic by putting all the interfaces in the same bridge group.

Basically this makes it into a completely flat network which is ok for very small topologies but does not scale well.

rsissons · ‎10-30-2002

Ob reflection, you could use NAT as in the following URL

http://www.cisco.com/warp/customer/556/3.html

But it is probably not worth it with only 20 users.

derrick · ‎11-05-2002

If I bridge the interfaces and create a flat network, do I still need to point the gateway of the individual PC to the routers? (I ask because currently the gateway is pointing towards the DSL modem?)

vkasacavage · ‎10-31-2002

There is another option here........one side could be 192.168.0.1 /25 and the other side could be 192.168.0.254 /25 .... this would create 2 unique subnets both in the 192.168.0.x range...........

or you could simply bridge all the traffic and disable IP routing as stated earlier. Or you just use a different subnet on the other side and not worry about it

moorj · ‎10-31-2002

Sounds like IP unnumbered would do the trick if you do not want to subnet out your private address space. Take a look at the below link for configuration example.

http://www.cisco.com/warp/public/701/20.html

Hope this helps.

Cheers, John.

CCIE#9332

derrick · ‎10-31-2002

OK, it looks like the bridging idea looks like it will accomplish what I am looking for. So can anybody tell me what is involved with briging an interface. (Generic commands should be enough to get me going. I hope.)

kholst · ‎10-31-2002

You will have bridge the traffic. Below is config for both routers :

no ip routing

int fa0

bridge-group 1

int s0

bridge-group 1

bridge 1 protocol ieee

thats it.

crgarcia3 · ‎11-06-2002

Another perspective:

The other way you can do it is to subnet the net from a /24 to a /25 yeilding 2 nets and enabeling routing - just use a different /30 for the serial interfaces. Should your company ever grow, you will be prepared for the growth.

DAVE GENTON · ‎11-06-2002

You need to also be aware that if you bridge the traffic as discussed in the thread you will be eating ALOT of the t1 up with traffic that should remain local to each LAN. Microsoft workstations send out lots of broadcasts on the local lan that will traverse your wan with bridging enable, you would be much happier if you routed your traffic.

d-

rsproul · ‎11-07-2002

dgenton is right about the broadcast traffic. A T1 is not that fat of a pipe and keeping broadcasts off of it is definitely advised. I concur with those who have suggested splitting your class C in two and routing between the two subnets. Bridging is not a bad solution but routing will prove to be more accomodating if your network grows.

From one of your other posts in this thread it sounds like you have a DSL connect to the Internet in here somewhere. This could present a minor issue with gateway assignments for your workstations. You may need to add multiple routes to the workstations that reside on the same subnet as the DSL router.