From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <47D55F3E.4030603@operations.com> Date: Mon, 10 Mar 2008 12:18:06 -0400 From: Lou Steinberg MIME-Version: 1.0 References: <47D05B55.404@operations.com> <2e59e6970803082338n20c9037p6ccae93654c58a69@mail.gmail.com> <47D3ED21.6050903@operations.com> <20080310082655.2f9cd485@extreme> In-Reply-To: <20080310082655.2f9cd485@extreme> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Bridge] bridge-utils and ppp List-Id: Linux Ethernet Bridging List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stephen Hemminger Cc: bridge@lists.linux-foundation.org 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