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Q: Routing between two subnets with 2 cisco 1720's ( No Answer,   0 Comments )
Subject: Routing between two subnets with 2 cisco 1720's
Category: Computers
Asked by: drewdykstra-ga
List Price: $25.00
Posted: 11 Sep 2006 13:28 PDT
Expires: 11 Oct 2006 13:28 PDT
Question ID: 764235
Our company is finishing the construction of a second building which
will be connected by a 54MBps Proxim Bridge.  Here's what we would
like to do:  We would like the two buildings to be on separate
subnets.  The host location's subnet is (class C we
own), and we would like the remote site to be
(Private).  For now we would like to run the remote site off of our T1
at the host site over the Proxim Bridge.  I have 2 Cisco 1720 routers
that I'm not sure how to configure to connect these two subnets.

Since the host and remote sites are being connected via the high speed
proxim bridge, these two subnets are essentially on the same physical
network.  I'm just not sure what kind of routes and IP's need to be
put into these two cisco 1720's.  I can get the network to the point
where I can trace through to the second router, but it stops there (I
can't reach a workstation or other device on the other subnet).  We
would like devices on both subnets to have the ability to communicate
back and forth.

Current non-working setup: 
Host 1720 ip -
Remote 1720 ip -
Remote 1720 secondary ip - secondary

Host Static Route

IP Routing is turned on for both routers.  Should I be doing something with EIGRP?

Any help would be appreciated.  Thank you!

Clarification of Question by drewdykstra-ga on 11 Sep 2006 13:41 PDT
From my limited routing experience (working with Cisco 1600's) I would
tend to think that we would need 2 ethernet ports on the router to
connect these two subnets (each configured on 1 of the subnets), but
the 1720's only have 1 fast ethernet port - with the ability to
purchase an additional 10Meg WIC Ethernet card...but we have our
network coming in over a 54MBs connection, so we don't want a 10Meg
ethernet card to restrict this.

I've been told it's possible to route between these two subnets (on
the same physical network) with a 1720 on each subnet...or was I told
wrong?  Thanks again.

Request for Question Clarification by gregaw-ga on 11 Sep 2006 14:31 PDT

Ideally you would want just one router on the host end that has two
10/100 network ports in it.  You would have one port assigned to each
network and there would be little to no routing involved.

If you have a router with two ethernet ports on each end you would
have to have a third network that would only contain the wireless
bridge devices and one port on each router.  The other port on each
router would then be for each sites local network.  This is ideal if
you would like to encrypt traffic across your wireless link using a

I'm trying to understand your setup.  Correct me where I'm wrong  You
have a proxim wireless bridge plugged directly into a switch or both
the host and remote sides.  You then have Cisco 1720's plugged into
those same switches on both sides.  You do not have anything else
plugged into either router (only one cable per router).

You can ping from either network to the other ends router, but not to
any workstations or devices.  This is the same from either end.

The one piece of information I'm not seeing is your default routes. 
Do you have another router connecting your network to the Internet? 
If your workstations and devices on your "host" network are pointing
to a different router than you will need to add a route to the
internet router.  If you do have another router connecting you to the
Internet this would be the Ideal place to hook up your remote network,
assuming that this router has an open 10/100 routable port.

Also be sure that you have a default route in the Remote side router
pointing to

What you are trying to do should work.  It will not be as efficient as
if you had a router with two network ports on the host end, but should

Any clarification from my above comments would be helpful.



Clarification of Question by drewdykstra-ga on 12 Sep 2006 13:37 PDT
You were right on with your description of the network.  We do have
another Internet Router (no availavle ports however) and I do have the
host site pointing to this as the default route.

After all of this torubleshooting, I finally discovered that my 1720's
were all configured properly - it was Windows Firewall running on our
workstations that was blocking the ICMP traffic and keeping my pings
and traces from reaching their destinations.  So everything is working
now!  Thanks for your help - I do wish that we were doing this a
better way with a router that has two fast ethernet ports on it.

Request for Question Clarification by gregaw-ga on 12 Sep 2006 13:58 PDT
I'm glad that it is working.

The best setup for you is to have one router with three ports.  One
for the internet and one for each part of your network.  Of course if
my company gave me everything on my "IT Wishlist" the company would go
broke.  Cost is always the limiting factor.

How many computers are at your remote site?  I've used the a Proxim
bridge with my previous employer and it always work well for us.

Clarification of Question by drewdykstra-ga on 12 Sep 2006 14:17 PDT
Glad to hear that I'm not the only person on a restrictive budget :). 
I picked up the 1720's dirt cheap on eBay.  Our Host site has 90
workstations and our remote site is projected to start with 20-25
workstations with hopes of growing quite a bit.

I was very impressed with how easy it was to get the Proxim Bridge
configured, secured, and running.  We're using the Proxim 5054R setup
for 54Mbps (of course this runs at half duplex, so we aren't actually
experiencing 54Meg each way).  The Proxim solution should pay itself
off in months (cost-wise) versus a point-to-point T1 - and obviously
the connection speed and ease of deployment makes it all the more
worthwhile.  We're only hopping about 300 yards across an intersection
(high roofs to avoid any semi's or the like), so we're receiving
maximum throughput.

Request for Question Clarification by gregaw-ga on 12 Sep 2006 15:11 PDT
The main concern that I would have with the way you are setup is that
even though you have two logical networks they are not seperated by a
router.  This causes an increased level of broadcast traffic on your
network.  With the number of workstations on your network it shouldn't
be a problem, but all those broadcast packets on your host network are
making that jump across the wireless link.  Particularlly with a half
duplex connection that can slow you down.  If the performace is good,
don't worry about it, but if down the road you do add more
workstations and start to feel sluggish at the remote side I would
invest in two routers.  One with at least three ports to sit at the
host side and connect to the internet, the host network, and the
proxim radio.  Then a second router at the host side with two ports,
one for the proxim radio and one for the remote network.  This keeps
your wireless network as pure as it can be and will give you the best
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