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IS BCP enabled on the fibre broadband?

LordFox
Grafter
Posts: 211
Thanks: 6
Registered: 10-03-2008

IS BCP enabled on the fibre broadband?

I've tried to bridge my PPPoE Dialer before, and could never get it to work on my Cisco routers. Experimenting with RouterOS has had similar luck, and I've just been told why.

Bridging the PPP requires BCP be enabled on both ends of the link.

So... is it enabled at PN's end?

3 REPLIES
legume
Rising Star
Posts: 170
Thanks: 11
Registered: 21-07-2013

Re: IS BCP enabled on the fibre broadband?

I don't understand the question really :-)

What is it you are trying to do?

LordFox
Grafter
Posts: 211
Thanks: 6
Registered: 10-03-2008

Re: IS BCP enabled on the fibre broadband?

I have a /29 subnet from PN; 6 usable IP addresses plus network and broadcast addresses.

That subnet needs bridging (switching, essentially) to a couple of servers that need to have public IP addresses directly assigned to them. So, locally, I have a public subnet running, and a private (192.168...) subnet for the normal PCs.

Don't worry, it's all well protected by a Cisco router/firewall.

The only way I can set this up (without BCP) is to have my modem/router in transparent mode, where it negotiates the PPPoE connection itself, and uses one public IP address (that assigned by PN to it) and has no private address. It effectively behaves as a layer-3 switch between me and PN with a bonus PPP dialer. The public address on the modem is my default route.

After that is a Cisco router which manages the routing and filtering. The Cisco interface connected to the modem needs to use another of my public addresses. So, that's two out of six gone just for the 'connection'.

What I have previously tried is to have the modem as just a bridge (no IP addresses) and have the Cisco do the PPP negotiation. That way, only one public address is needed (on the Cisco's PPPoE dialer interface). That is fine. But...

...if I then try to bridge the dialer with the public address onto my local public network for the servers, like I could with any other interface, the dialer interface fails and routing stops. I could never figure out why, but someone just told me the answer on another forum.

BCP! BCP is a protocol to negotiate PPPoE bridging; just what I am trying to do. Without BCP on both ends of the link, there is no way for the dialer to become a L2 interface and let the bridge interface take over as the routed interface for the PPPoE. That's probably a simplification and not perfectly accurate, but since I doubt BCP is enabled there's not much point in me reading up on the specifics.

 

legume
Rising Star
Posts: 170
Thanks: 11
Registered: 21-07-2013

Re: IS BCP enabled on the fibre broadband?

It seems to me from https://tools.ietf.org/html/rfc3518 that BCP would be for bridging two remote sites that you control.

I don't think PN would want to be one end of your LAN.

 

If you are on FTTC then historically Openreach issue "modems" were already set up as bridges for you. I still use them and do my own pppoe on a PC.

 

Your router/modem clearly can't do "proper" bridging. From an interface POV on FTTC Openreach expect a vlan and this is bridged by their modems to normal ethernet, so your pppoe discover (ethernet broadcast) goes out and a reply from a some mac  address comes back. Because OR do multicast not all traffic goes over the PPP anyway, you are expected to isolate multicast which routers with WAN ports do. If you have a TV product the multicast does not come over ppp and if you don't isolate and use bulk multicast on your lan it will go up the bridge and eat your upstream bandwidth.

 

As for not loosing ip addresses - way back when I first had adsl I used a router with open firmware (routertech) so basically linux. With a single IP address it was possible to set things up so ppp0 had no address and something on the LAN had it. You needed a local address on the router and a host route for the wan ip to get things to work - bit of a hack really - but then not using locked down kit lets you do things like that.

 

When I later got a /29 (still adsl) I found I could use all 8 as far as the ISP was concerned - again just a hack nat set up to test if it worked rather than normal setup - I didn't need 8 anyway.

 

I don't know anything about cisco kit and only think of bridging as a layer 2 thing so when I see a phrase like

"if I then try to bridge the dialer with the public address onto my local public network for the servers"

 

I am totally lost/baffled :-)