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How to configure a leased line using Cisco 1721 routers (ILC; Layer 2; Point-to-Point Protocol) by  bridging method.

Posted on 2004-09-21
Medium Priority
Last Modified: 2008-01-09
Hi Guys, I need your expert help on this as I am a little new at this technology.
I need to connect two networks between Sydney(S) and Manila(M) using Cisco 1721 routers.The requirement is to use the same IP subnet in both locations.

(The router consist of  one WIC 1T Module (Serial0), one 10/100 Ethernet port (FastEthernet0)  and CAB-X21MT and CAB-V35MT cable for Sydney and Manila connection respectively.
Note:The router at S site connects to the CSU/DSU using X21 connection and the router at M site connects to the CSU/DSU using V35 connection).

Our Ethernet LAN using 123.11.x.x; ;

I plan to configure/use the IP address for routers as follow:
S router-  IP: ; SM:
M router- IP: ; SM:
bridge group 1              (???)
bridge 1 protocol ieee   (???)

-I am not sure what 's bridge group or bridge protocol to use here- What 's different ?

Pls explain what 's need (parameters) to be configured for this to work? and what step/command should be take to configure the routers?

Thank you and Kind Regards
Livingstone IT

Question by:livingstoneitdept

Assisted Solution

moe_740 earned 200 total points
ID: 12119986
hi there,
I would say that its better to split the locations in to two subnets to avoide broadcasting between the two sites.
unless you really need it this way, then you can choose bridging tech. instead of routing.
more info needed:
how many machines in each side? (around)
servers reside on one or both sites?

Author Comment

ID: 12120293
I need to setup this way so that I can share the network management/monitor tools, antivirus ect.. (softwares).
(I understood that this would cause the single broadcast domain as both networks use the same subnet)

More info:
-Sydney site ~ 150 machines and all servers are resided here.
-Manila site ~ 20 Machines (Clients only) and one VoIP for ~ 20 phones.


Assisted Solution

Marakush earned 200 total points
ID: 12122289
Okay I can see two ways to do it off the top of my head.

1. VPN and have a DHCP assign IP addresses to the Manila site.

2. You would need a class C block and have to split the IP addresses in half and assign half to Sydney and half to Manila.

Personally I would pick the first one, its much easyer.

Hmmm also for the Sydney site you might want to consider using Citrix and just have a stray address for the VoIP.

Okay hope this tidbit helps.


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Expert Comment

ID: 12123928
Whoa...its been a while since I've seen bridging across a WAN.  If you really, really want to/have to do there is a link at the end.  Basically just address your ethernet interfaces and WAN interfaces as normal.  Ethernet interfaces will be on the same subnet.  WAN and LAN interfaces must be a member of the same bridge group.

interface Ethernet0
ip address w.x.y.z
bridge-group 1

!--- Assign this interface to Bridge Group 1
!--- Frames are bridged only among interfaces in the same group
!--- Note: the dialer1 interface is also in this bridge-group 1

interface s0
ip address a.b.c.d
bridge-group 1

bridge 1 protocol ieee

This should get you started:


Author Comment

ID: 12128072
ok,more info -
-Our existing network in Sydney used this range of private IP 123.11.x.x; and we are running Citrix here.
-Manila network is new (to be setup similar to Sydney network -will use the similar IP address range).

When you mention about the dial1 interface- I 'm not sure if we require to set up this (the link is layer 2, PPP (like mirroring) and this was setup by the ISP ). The router only have 2 interfaces-Serial0 and Fastethernet0.
Let 's get the terms (words) correct as we discuss, when you talk about WAN and LAN interfaces,
Wan interface = Serial0  ; LAN interface = FastInternet0   , are they right?
also you are suggesting to use subnet (LAN) and (WAN). will they work with the Sydney network (

Do you think the configuration below would work?
interface FastEthernet0
ip address 123.11.y.z
bridge-group 1

interface Serial0
ip address 123.11.c.d
bridge-group 1

bridge 1 protocol ieee



Expert Comment

ID: 12129793
The dialer0 interface in the article was for ISDNso it is not relevant.  You config for fa0 and s0 is what I would try.

I really, really need to try and talk you out of doing this bridging.  170 machines broadcasting across a WAN is excessive.  In fact 170 machines in the same subnet/VLAN on a local network is excessive by today's network design standards.  Can we go back and review your business need to do this?  

Author Comment

ID: 12137693
Ok, It 's seem that bridging is not recommended/suitable for our environment.
 Should I use IP routing method instead? again this is my first time doing this, I do'nt have much knowledge about this technology, please help/guide me through (in details) of how to do this- thks.

Expert Comment

ID: 12137872
Starter questions:

Are your T1s installed at both ends?
Is this point-to-point T1, frame-relay or something else?
What is the network addressing on each of the two lovations?
Is their a router/layer-3 switch in place on either LAN?
Is there a firewall/internet access at each location?

Once we have the answer to these questions, we can develop configs for your routers and get you up and running.


Author Comment

ID: 12138950
1- Not T1 connection but an ILC (International Lease Circuit)/256KB installed at both ends.
(Sydney site - CSU/DSU; X.21 connection - ie: Sydney Router 1721 connect to the CSU/DSU via the X.21 cable  ; Manila site: CSU/DSU ; V.35 connection-ie Manila route 1721 connect to the CSU/DSU via V.35 cable)

2- It is point-to-point ILC/256KB  - (it 's a direct link b/w Sydney amd Manila - like mirroring or back-to-back)

3- Network address
Sydney:  IP (Lan) : 123.11.x.x
               Subnet  :

Manila:   IP (lan)  : 123.11.10.x
             Subnet   :  

(Can i use the same subnet as Sydney- ?or I must use a differenr subnet?)

4- There is no route/layer-3 in place on either LAN.

5- Yes there is firewall/Internet access at Sydney site  and NO firewall at Manila site.

Sorry the way I explain things here. are they make sense to you ?


Expert Comment

ID: 12139796
You should have both networks (LAN) as different networks.  The WAN link will be a third network.

1- are both circuits installed?
2- have you connected the routers to the circuits?
3- I am going to assume that the ILC circuit will be configured like any other serial interface.
4- Do you own the routable address block that you are using on you LAN?  Current recommendation is to use RFC1918 "non-routable" addresses for private networks.
5 - We will need to develop a network diagram so we don't miss anything

Are you located at either of these sites?

Author Comment

ID: 12140338
1- At the moment, only one circuit is installed in Sydney site. Manila site to be installed sometime next week.

2- The router are not connected yet. (still waiting for complete link)
-I need to pre-configure the Manilar router and send it there 1st - someone will be there to help/change the required setting.

3-I think the ICL circuit is configured like other Serial Interface ( The only info was provided from the Line Leased company is that this link is the  ILC/256Kb, Layer-2, Point-To-Point, direct back to back connection - and they said that it 's upto us to establish our own IP addresses that suit our LAN, No other info was given)

4- I 'm not sure about this question- Routable address block? Is this Our LAN IP Address? pls explain further.

5-yes pls. Is there any further info you need that I could provided?

Sydney-always someone available. Manila- There will be someone at the time/date of the installation.  


Accepted Solution

netspec01 earned 1600 total points
ID: 12143062
> (The router consist of  one WIC 1T Module (Serial0), one 10/100 Ethernet port (FastEthernet0)  > and CAB-X21MT and CAB-V35MT cable for Sydney and Manila connection respectively.

Another item.  Since you have external CSU/DSU, you will not need the WIC-T1.  The WIC-T1 is a CSU/DSU.  You will need to use the 60-pin serial port and not the WIX-T1.

Net diagram (Sydney to Manila)

PC----switch-----router----CSU............<ICL circuit>........CSU-----router-----switch-----PC

Addressing scheme:

Sydney = LAN addressing: (leave as is for now)
              router S0/0:
              router fa0/0: (or other open ip address)
              - need static route to Manila

Manila = LAN addressing:
              router S0/0:
              router fa0/0:
              need static route for Sydney

This is a rudementary outline of what needs to be done.  Without any Cisco IOS experience I can tell you from experience that this forum is not the best way to get your router configured and up and running.  You shouild seek some professional assistance in getting your routers configured and bringing up your circuit.

Since your original question was how to do bridging and this has been answered, you should award the points and close this question.

Author Comment

ID: 12314106
Thank you all for your great support.
Special thanks to Netspec01 for your prompt and informative response, we realy appreciat it.

Expert Comment

ID: 12325432
Glad to help out!

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