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Transparent Bridging issue

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  • Routers
  • Modem
  • Networking
Last response: in Networking
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March 16, 2011 3:49:07 PM

Hello, hopefully someone out there can enlighten me as to a possible solution for this:

I have a 12Mb DSL connection through Qwest and use a Zyxel PK5000z modem with it. Behind the modem is a Cisco 1821 router. Now the modem is in transparent bridging mode, that is to say that data passes through the modem to the router as if the router was the first hop, not the modem. The router has the same IP address as the modem (static from Qwest). My problem is this, I purchased a block of 5 static IP addresses from Qwest and I am wondering if they are useless. I've attempted to also plug a laptop directly into the modem (4 port switch built in) and set up a WAN miniport PPPoE on it. It connects and authenticates just fine and can ping popular websites (Google, Yahoo) but it cannot browse any websites nor does email work through it. On the PPPoE connector I used the same IP address as the modem (won't authenticate with any other address) and on my ethernet adaptor I used various static addresses from my pool, all to no effect. It should be noted that when I do connect up with the laptop, the router then drops it's connection and vice-versa.

I could certainly connect the laptop through the 1821 and it would work. My goal here though is to make use of the 4 port switch built into the DSL modem and the block of 5 static IP addresses I purchased. Is the use of Transparent Bridging utterly limited to a single connection through the DSL modem?

Any help with this problem would be greatly appreciated.

More about : transparent bridging issue

March 16, 2011 4:39:31 PM

Without getting into the nitty-gritty details (at least not yet), this situation calls for a different approach than your typical consumer router. Either you need to disable NAT completely (and then all devices receive public IPs behind your switch), OR, use a NAT that supports multiple public IPs (i.e., maps each public IP to a local IP).

So before going further, how have you configured NAT on the Cisco?
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March 16, 2011 5:46:01 PM

The router (and NAT along with it) is setup for a VPN connection to another location. NAT is enabled on both the Inside and Outside (PPPoE Dialer) interfaces, though the NAT-TRAFFIC access-list is solely for Inside traffic.
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March 21, 2011 10:34:39 PM

The more I consider this problem, the more I am convinced there is no viable solution.

Please close this thread.
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