[cisco-bba] PPPoE with Routed Subnet

[Brian Raaen]

Patrick,
	If this is like most of the PPPoE setups I have worked with (I work on the 
service provider side of things) you would have a static that is assigned to 
the wan of your router using ipip, and the /29 is routed to that 
address(think - ip route $subnet 255.255.255.248 $static).  When that subnet 
hits your router you can do pretty much anything you want to with it.  We 
usually suggest that customers assign the first usable to the lan of their 
router (usually ala linksys variety) and make sure that nat(or gateway mode) 
is turned off.  They would set up their internal host using an ip out of the 
subnet with the router internal as their gateway.  Some customers even add a 
second router for NATing (if you are using lo end soho routers that may be 
your only option).  Since you are using a IOS powered cisco you can look into 
using something like 1:1 nat to allow you to use all 8 addresses in the 
subnet if you want to make sure to use one for pat (i.e. standard nat) if you 
need to.


----------------------

Brian Raaen
Network Engineer
braaen at zcorum.com

On Sunday 11 January 2009, Patrick Wu wrote:
> Hi Everyone,
> 
> I have a DSL connection running PPPoE with a routed subnet, the service
> provider indicated that it will use the 1st IP address of the routed subnet
> for the router (WAN?), and the rest of the IPs of the subnet can be assigned
> to the hosts behind the router.
> 
> What I want to know is whether I need a bridged interface between the WAN
> and LAN side of the router (Cisco877), and what configuration will help me
> achieve this?
> 
> Thanks to all!
> 
> What I have so far (was doing NAT before, but probably will remove it
> later):
> 
> interface ATM0
>  no ip address
>  no atm ilmi-keepalive
>  dsl operating-mode auto
>  service-policy output SIP-priority
> !
> interface ATM0.1 point-to-point
>  description $FW_OUTSIDE$$ES_WAN$
>  pvc 8/35
>   pppoe-client dial-pool-number 1
>  !
> !
> interface FastEthernet0
> !
> interface FastEthernet1
> !
> interface FastEthernet2
> !
> interface FastEthernet3
> !
> interface Vlan1
>  description $ETH-SW-LAUNCH$$INTF-INFO-HWIC 4ESW$$ES_LAN$$FW_INSIDE$
>  ip address 192.168.0.1 255.255.255.0
>  ip nat inside
>  ip virtual-reassembly
>  ip tcp adjust-mss 1412
> !
> interface Dialer0
>  description $FW_OUTSIDE$
>  ip address negotiated
>  ip mtu 1452
>  ip nat outside
>  ip virtual-reassembly
>  encapsulation ppp
>  dialer pool 1
>  dialer-group 1
>  no cdp enable
>  ppp authentication pap callin
>  ppp pap sent-username xxxx at xxxx password 7 xxxx
> !
> ip forward-protocol nd
> ip route 0.0.0.0 0.0.0.0 Dialer0
> !
> ip nat translation udp-timeout never
> ip nat inside source list 1 interface Dialer0 overload
>