Bridged APN

david at david at
Tue Apr 7 19:23:17 UTC 2020

The reason this is something people want is that the UE in bridge mode can
offer a public IP to a router behind the UE.  I do agree that this is likely
something very proprietary.  A proxy-ARP would be good but I am not sure how
that would work in the UE.

David Peterson
Senior Engineer
855-947-7776 ext. 9214
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-----Original Message-----
From: Harald Welte <laforge at> 
Sent: Tuesday, April 7, 2020 2:52 PM
To: david at
Cc: nextepc at
Subject: Re: Bridged APN

Hi David,

On Tue, Apr 07, 2020 at 06:18:23PM +0200, Harald Welte wrote:
> On Mon, Apr 06, 2020 at 04:29:21PM -0400, david at wrote:
> > Does anyone have any experience with a bridged APN on Open5GS?
> As far as I know, 3GPP didn't really introduce "Ethernet" type PDN 
> contexts until very recent releases.  For a long time, IPv4, IPv6 and 
> IPv4v6 were the only available options.

I just checked: Etehernet type PDN connections are only supported in 5G, but
not in 4G/EPC.  Even Releae 15 doesn't mention it at all.

So whatever some vendors may be offering, I would bet it is not really any
actual Ethernet bridging.  It may be more something like proxy-ARP on the
PGW side, but still only passing IP over the 4G network.

The big question is: What is it used for, and what are the requirements of
that use case?  A real Ethernet bridge would be transparent regarding the
MAC addresses on both sides.  And that's what I'm stating is not possible
over 4G as per 3GPP specs.

- Harald Welte <laforge at>
"Privacy in residential applications is a desirable marketing option."
                                                  (ETSI EN 300 175-7 Ch. A6)

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