We use Cisco 891 routers as CPE for several client sites. They are all running IOS 15.

Cisco IOS Software, C890 Software (C890-UNIVERSALK9-M), Version 15.0(1)M8, RELEASE SOFTWARE (fc1)

The majority of these sites terminate against an external ADSL2 modem which we put into bridge mode (I can't recall the exact bridge mode, but basically the modem just passes everything through).

We rely on our Cisco 891 devices for PPP session termination, NAT, etc... And I've come up with the below config, we've been successfully for some time with our main ISP, its been working fine:

interface GigabitEthernet0
 description WAN PPPoE ADSL2+
 bandwidth 1024
 bandwidth receive 20480
 no ip address
 ip nat outside
 ip virtual-reassembly
 duplex auto
 speed auto
 pppoe-client dial-pool-number 1

interface Dialer0
 description ADSL2+ Dialer Interface
 bandwidth 1024
 bandwidth receive 20480
 ip address negotiated
 no ip redirects
 no ip proxy-arp
 ip mtu 1492
 ip nat outside
 ip virtual-reassembly
 encapsulation ppp
 ip tcp adjust-mss 1452
 dialer pool 1
 dialer-group 1
 ppp authentication chap pap callin
 ppp chap hostname [email protected]
 ppp chap password 0 XXX
 ppp pap sent-username [email protected] password 0 XXX
 no cdp enable

However, in the last few days our ISP has made some changes which has affected a few customer sites, and they've said we need to ensure that all CPE are using "PPPoA and VC Mux encapsulation"


I've been looking at some existing Cisco CPE and cannot figure out a way to ensure we are using PPPoA, or a way to force that if not. It looks like, right now, that we're using PPPoE:

PPPoE vaccess, cloned from Dialer0

All config examples I've found are using ATM interface which allows specification of PVC, encapsulation settings etc...

I can understand that things like PVC settings are modem-related and so would not be in the router config as our routers do not contain the modem functionality. But, can I assume that once the traffic has passed the modem to the WAN interface on the router, the ATM cells have been converted to Ethernet packets, and is this why there is no way (that I can see) to configure PPPoA instead of PPPoE?

1 Answer 1


Technically, you're doing PPPoEoA.

The VC Mux part will have to be set on the modem, as that's the only thing that has access to the ATM layer. If you had a dsl interface in the router, you'd do:

blue-gw#show run int atm0.1
Building configuration...

Current configuration : 131 bytes
interface ATM0.1 point-to-point
 bandwidth 6000
 pvc dsl 8/35 
  encapsulation aal5mux ppp dialer
  dialer pool-member 1

Other devices will vary.

  • 2
    You cannot have true bridging when doing PPPoA unless your Modem device supports reincapsulating your PPP session from something you can use over Ethernet to PPPoA. The old Alcatel SpeedTouch terminal adapters (modems) had a PPTP mode that allowed you to establish a session with the adapter using the ISP authentication parameters. The adapter would then pass over the credentials to the ISP's PPPoA session.
    – ItsGC
    May 22, 2013 at 6:42

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