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Guan Foo Wah 10-05-2004 03:44 AM

Setting up Cisco 800 router as transparent bridge to the internet
 
Dear all,

I am very new at configuring cisco equipments and would require much
help.

Currently I have a Cisco 800 router series with ADSL interface that
dials to the internet. My ISP assigned 5 fixed IP address to my
company (all IP belongs to the same subnet) and so far only 1 IP
address is used for that cisco 800 router.

My company has already purchased a Cisco Pix 501 and plans to it to
the public network. My company wants to minimise the public IP being
use for future expension. So rather than having public 2 IP being used
(one for 800 router and one for 501 pix), only 1 IP should be used. My
company propose that the 800 router would be setup as a transparent
bridging and the Pix 501 would assume the 800 router public IP
address.

So how can I setup transparent bridging for the cisco 800 router? I
did some research on this subject and found some clue that I can make
the internal and ADSL interface of the 800 router belongs to the same
bridge group using the bridge-group command. However, I have some
doubts on this. I would need your inputs if this can really work or
someone can point me where I can some answers.

Thank you very much.

Walter Roberson 10-05-2004 09:37 PM

Re: Setting up Cisco 800 router as transparent bridge to the internet
 
In article <6bfa3c29.0410041944.5d545303@posting.google.com >,
Guan Foo Wah <jgfw@hotpop.com> wrote:
:So how can I setup transparent bridging for the cisco 800 router? I
:did some research on this subject and found some clue that I can make
:the internal and ADSL interface of the 800 router belongs to the same
:bridge group using the bridge-group command.

That would be the approach to take.

:However, I have some doubts on this.

On some Cisco routers, some kinds of interfaces may not be
included in a bridge group; I haven't examined that point for the
800 series. Consider, though, that if your ADSL link requires PPPoE
then the received PPPoE packets should NOT be transparently bridged
over to the ethernet side without having stripped out the PPP layer.

If you do run into this limitation, then what you could do (in theory!)
would be to route the incoming packets from the ADSL interface over
to a loopback interface, and bridge-group the loopback interface to
the ethernet interface. To get this to work properly might require
assigning an IP to the BVI (so that the ADSL interface can route
to it); in that case, you would assign an IP in one of the reserved
IP address ranges, and have the external interface of the PIX be
assigned in the same subnet.


:Currently I have a Cisco 800 router series with ADSL interface that
:dials to the internet.

I take it that the 800 series router ADSL interface is acting as the
ADSL modem, and not just doing PPPoE over an ethernet interface
to an ADSL modem provided by the ISP? If you -were- using the 8xx mostly
for doing PPPoE encapsulation and not as an ADSL modem, then you
could potentially eliminate the 800 series, as the PIX 501 will do
PPPoE on its outside interface.
--
Will you ask your master if he wants to join my court at Camelot?!


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