BGW320-500 Bridge Mode and/or IP Passthrough Question

If you have purchased a Static IP block, then what you want is cascaded router.  The network set up in the Cascaded Router section will be given all traffic that arrives from the Internet for that subnet block and the public subnet traffic from that address will be routed to the Internet.

1. Connect your Ubiquity Dream Machine Pro to a Gateway LAN port, and let it get a LAN IP via DHCP.  
2. Go to the Gateway's Home Network > IP Allocation page and click allocate so that the Gateway reserves that IP address for your UDMP.
3. Go to the Gateway's Home Network > Subnets & DHCP page, turn on Cascaded Router enable and fill in that IP address in Cascaded Router Address, and the network address of your block in Network Address.  The mask should already be correct at 255.255.255.248.
4. Your UDMP now owns that subnet.

Yes, this does create a hop at your Gateway, but it is not as expensive as the hop you get from IP Passthrough or just plain NAT.

Wow thank you. Cascaded router is entirely new to me, I’ll look this up. Thank you.

what do you mean about this being a less expensive hop? (Your last sentence)

thanks 

Based on reports from users on these forums: When you turn on IP Passthrough to a router, it appears that the connection from the Router to the Gateway is slowed down such that traffic doesn't flow as fast as either one is capable of.  This is only noticeable for Fiber service, if you're below 200 Mbps, there doesn't seem to be a drop off (e.g. for my VDSL2 connection, it doesn't hurt at all).  The Gateway maintains a session in the NAT table for the traffic, even though it's not actually performing NAT.  Those who have added a Public Static have reported it ran faster than their IP Passthrough traffic ran previously.

Regardless, IP Passthrough has no meaning for a public static block.  IP Passthrough only affects traffic at the Dynamic Public Address, traffic arriving from a public static would not be affected at all by the existence or absence of IP Passthrough.

Got it, thank you. And as I do have 1gbps fiber I do care for maximizing throughput.

so if ip pass through is for something completely different, what is “bridge mode”? I’ve been told that this is what I really need (but isn’t supported by the AT&T device)..?

Bridge mode means that the "modem" doesn't do any Level 3 processing on the traffic and passes it through, sort of like an Ethernet switch, e.g. you wouldn't see a HOP in traceroute.  With the AT&T Gateway you cannot achieve a true bridge mode. The best you can do is:

• For a static public subnet: the Cascaded Router (if you want to use a router to manage the public subnet)
• For the dynamic public subnet: IP Passthrough (or DMZplus on the Gateways that call the feature by that name).

Thank you, really appreciative of your explanations. Just curious, if you know, why att doesn’t allow true bridge mode?

Many reasons:

(1) The Gateway is designed to also handle VOIP for AT&T Phone and IPTV for U-verse TV and those require the level 3 functionality,

(2) AT&T wants to be able to control authentication, and their choice of mechanism to authenticate requires level 3,

(3) AT&T reserves the right to manage traffic, which is much easier to do with a Level 3 device.,

(4) Once a Gateway is placed in true bridge mode, it appears dead to users who didn't mean to get it that way.  

Perhaps one additional question: since I don’t use VOIP or any other feature, should I ask for (or upgrade to) a business customer gateway? I’m not sure if that is even available but wouldn’t it be better all around to replace the AT&T consumer all-in-one with a simple dedicated business device?

For the class of service you have, there is no better gateway.  You're basically using a single fiber split 32 (IIRC) ways.  If you want your own dedicated fiber service and control over how it is terminated, that's a vastly different, and vastly more expensive, type of service.

You mean split with 32 neighbors?