Re: [Bridge] bridge-utils and ppp

[Lou Steinberg <lspam5@operations.com>]

Stephen-

Stephen Hemminger wrote:

> 
> The bridging code only works for devices that have Ethernet headers.
> That is the way the bridging 802.2 standard works, it is a Layer 2 bridge
> and it uses the address information from Ethernet to do routing.
> 
> PPP does not use Ethernet level framing so it can't be bridged.
> What were you trying to do? there are plenty of other ways to get the
> same effect.

Makes sense, I suppose (The forwarding is complicated by a p-p link 
without a destination mac addr that looks like ethernet).  I expected 
that someone had built a table to do the mappings because the docs I 
referenced in the original post specifically say that ppp can be bridged.

What I'm trying to do is a simple/low latency forward from a vpn 
concentrator/firewall/router out to a cellular WAN modem that attaches 
to a USB.  My firewall lacks the USB interface so I simply need to 
forward packets between the USB and ethernet.  Am doing it now at layer 
3 (using iptables to do NAT) but that adds a lot of complexity and my 
firewall already does NAT (so it's happening twice).    I haven't yet 
tested an ipsec tunnel over the link, but am concerned that I may also 
need to add ipsec passthrough if I do this at layer 3.

All in all, a simple layer 2 forward between eth0 and ttyUSB0 is what I 
really need.

/Lou