1801 Bridging question

[mark48319]

Is it possible to configure a router in the following way, if so can somebody please point me in the right direction?

At one of our sites we have an 1801 which is connected to the internet using the DSL interface, and to the internal network using the switch ports. We have another company who are installing a second router for a static VPN, and they want it to have an external IP address assigned to it.

We are on a /31 subnet, so only have 2 useable IP addresses, but currently only use one of the IP addresses.

We would like bridge the DSL interface and the (currently unused) interface FastEthernet 0, so that the other company can connect their router to FastEthernet 0 using the second external IP.

I have tried doing so, but as the DSL connection is using PPP it goes down as soon as it is added to a bridge group.

This is the current ATM / dialler configuration we are using:

interface ATM0
no ip address
no atm ilmi-keepalive
dsl operating-mode auto

interface ATM0.1 point-to-point
pvc 0/38
  encapsulation aal5mux ppp dialer
  dialer pool-member 1

interface Dialer0
ip address xxx.xxx.xxx.xxx 255.255.255.248
ip nat outside
ip virtual-reassembly
encapsulation ppp
dialer pool 1
dialer-group 1
ppp authentication chap pap callin
ppp chap hostname username
ppp chap password 0 password
ppp pap sent-username username password 0 password

Any advice would be greatly appreciated.

[Lei Tian]

Hi,

Are you trying to do transparent bridging across WAN link? Like the example in this link:

http://www.cisco.com/en/US/tech/tk331/tk660/technologies_tech_note09186a0080094471.shtml#ex3

I think you can only do that if your WAN link is p2p.

HTH,

Lei Tian

[mark48319]

Hi

No, I am not trying to bridge accross a WAN link.

We just need the 2 routers (the 1801 and the router being supplied by an external company) to each have one of our 2 external IP addresses.

The 1801 will be connected to the ADSL line, and the other router will be connected to an ethernet interface of the 1801.

The 1801 would also be the default gateway on our network, performing NAT and port forwarding.

Mark

[paolo bevilacqua · Accepted solution]

We just need the 2 routers (the 1801 and the router being supplied by an  external company) to each have one of our 2 external IP addresses.

You cannot do that with PPPoA, as it a non-bridgeable protocol (it does not have mac addresses). You need the ISP to switch to RFC1483 in order to do what you described above.

[mark48319]

I did wonder if that might be the case.

Thank you for your help.

Mark

[paolo bevilacqua]

You are welcome, thank you for the nice rating and good luck!