I have a Thomson TG508v2 router/modem and a brand new AirPort Extreme connected to it.

At first, I set the AirPort Extreme to "share a public IP", which enables DHCP/NAT. Everything works great but I was having the Double NAT error.

So I set the AirPort Extreme as bridge mode, which disables DHCP/NAT and let my crappy modem handle my internal network IPs.

Will this cause any performance hit in my network? I'm worried because I'll outsource this job from AirPort Extreme (premium hardware) to the crappy modem.

Before you suggest, I tried setting my modem as a bridge and configuring PPPoE on the AirPort Extreme, however it wouldn't connect to the internet, so I just dismissed leaving the modem as bridge.


If you have NAT on, on both devices, then they will both be doing NAT on all outgoing/incoming frames, and thus will both cause a performance hit. It's not like having the AirPort Extreme doing NAT first is somehow taking some of the load off of the DSL modem if the DSL modem is doing NAT as well.

Turning off NAT on your AirPort Extreme will keep your AirPort Extreme from adding a small performance hit to your traffic, but I agree with your sense that leaving your TG508v2 to do NAT is probably a suboptimal solution. I'm guessing the NAT engine in the AirPort Extreme is higher quality than the one in the DSL modem, so if there's any way to get your DSL ISP to switch out your TG508v2 with a bare-bones modem that doesn't do NAT, that's the best way to go.

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    Unless you have some really crappy hardware the 'performance hit' of NAT really isn't that much, at worst it may add a couple ms of latency. I doubt he will see much of a difference either way. What you do get with multiple NAT setups is needless complexity. – Zoredache Feb 24 '12 at 1:02
  • I set the TG580v2 as bridge and disable its DHCP. Now I can't access its configuration page. APE is set as PPoE and to share the public IP (DHCP+NAT on). I noticed that the router address is kinda strange (not a private IP) as shown in this screenshot: img17.imageshack.us/img17/3284/34549221.png - Is there anything I can do to access the modem page again keeping this configuration? – user117313 Feb 24 '12 at 12:46
  • The NAT on the Airport Extreme tops out at around 30mbit for me, IIRC. Turning it off allows me to nearly saturate the wireless at 100mbit. – pestilence669 Mar 23 '13 at 17:28
  • @user20808 That sounds like maybe an older model. There have been 6 generations of devices called AirPort Extreme, with significantly different CPUs, Wi-Fi radios, and Ethernet interfaces. I know that recent ones get hundreds of megabits of TCP throughput through the NAT and can saturate the (450 mbps PHY rate) wireless at close to 350 megabits/sec of TCP throughput. – Spiff Mar 24 '13 at 6:32
  • @user117313 A modem in bridge mode leaves nothing to configure. It just copies the data from one port to the other. – David Schwartz Oct 12 '13 at 23:11

First off, having both in NAT mode will cause latency problems, as someone else said here a few ns, but sometimes if you are a gamer 50ns is better than 150ns, and yes I speak out of experience, DSL can be rather slow at times.

In any case, if you put your router in Bridge Mode, for all intended purposes you have just done as it said, made it a bridge, it's not accessible any more, it is a pipe full of data not a pipe with a civ at the end of it.

If you want to change it, you are going to have to either plug directly into it, or more realistically put, you are going to have to reset it.

I would honestly keep the modem as a bridge, and use your Airport Extreme for everything else, you will see a speed boost. My only worry is this, some routers given by ISPs don't like when that happens.

You may be better off buying a DSL modem, put it into bridge mode, and let the AE do all of the work.

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