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Topic # 165836 22-Feb-2015 12:07
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Recently I needed a simple ADSL to Cisco router connection that would avoid consumer NAT issues without spending a lot of money on an new ADSL WIC. This tutorial assume a static IP allocation (otherwise why would you be doing this?).


There have been a few posts here on using the Linksys AM300 in half bridge mode, for example:

In addition there is this useful overview:


Linksys AM300
Firmware version: 1.19.04 Cisco ISR
IOS version: Anything after 12 should be fine.


Set your PC to static IP in the subnet not equal to
Browse to

Factory reset of the Linksys AM300. Then set the following (this is for Telecom/Spark ADSL2+):  Mode: RFC2364 PPPoverATM

 Modulation: ADSL2+
 ATM settings: VPI=0, VCI=100, VCMUX
 Ticked Half Bridge mode
 Password: password
 Disabled the DHCP server

The Linksys DHCP server does not give exactly the right settings and unless you fiddle with the broadcast address ( vs set in the Cisco router config register) you may find that he Cisco interface does not work in DHCP mode. So I disabled the DHCP server in the Linksys and used a static allocation in the Cisco.

The variables not well covered in the past posts on Geekzone were the gateway and subnet settings.  As noted in the wlug, post many half bridge home routers implement a virtual gateway at the public IP address plus one.  This proved to the case with the AM300.  Note that this virtual gateway is not the Telecom/Spark gateway reported on the AM300 status page which is in an unrelated subnet.  Knowing the gateway IP we can then calculate the net mask in my case  This mask is valid when the public IP and gateway differ by just the LSB, YMMV.
Here is the Cisco interface and route of last resort config:

interface GigabitEthernet0/1
 description public ADSL circuit with static IP
 ip address 219.88.X.Y
 ip access-group 100 in
 ip nat outside
 ip virtual-reassembly in
 duplex auto
 speed 100
 no mop enabled
ip route 219.88.X.Y+1

where X and Y are the actual IP for your circuit.

The ADSL at this site was not that fast, 10Mbps down and 1Mbps up.  In this application avoiding NAT and a low latency rather than speed were the key criteria. Moving from the AM300 running on it's own to the AM300 plus Cisco router, the ping time was reduced from 18 to 9 ms according to


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  Reply # 1244078 22-Feb-2015 12:07
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Hello... Our robot found some keywords in your post, so here is an automated reply with some important things to note regarding broadband speeds.



If you are posting regarding DSL speeds please check that



- you have reset your modem and router



- your PC (or other PCs in your LAN) is not downloading large files when you are testing


- you are not being throttled by your ISP due to going over the monthly cap



- your tests are always done on an ethernet connection to the router - do not use wireless for testing



- you read this topic and follow the instructions there.



Make sure you provide information for other users to help you. If you have not already done it, please EDIT your post and add this now:



- Your ISP and plan



- Type of connection (ADSL, ADSL2, VDSL)



- Your modem DSL stats (do not worry about posting Speedtest, we need sync rate, attenuation and noise margin)



- Your general location (or street)



- If you are rural or urban



- If you know your connection is to an exchange, cabinet or conklin



- If your connection is to a ULL or wholesale service



- If you have done an isolation test as per the link above



Most of the problems with speed are likely to be related to internal wiring issues. Read this discussion to find out more about this. Your ISP is not intentionally slowing you down today (unless you are on a managed plan). Also if this is the school holidays it's likely you will notice slower than usual speed due to more users online.



A master splitter is required for VDSL2 and in most cases will improve speeds on DSL connections. Regular disconnections can be a monitored alarm or a set top box trying to connect. If there's an alarm connected to your line even if you don't have an alarm contract it may still try to connect so it's worth checking.



I recommend you read these two blog posts:



- Is your premises phone wiring impacting your broadband performance? (very technical)



- Are you receiving a substandard ULL ADSL2+ connection from your ISP?

I am the Geekzone Robot and I am here to help. I am from the Internet. I do not interact. Do not expect other replies from me.

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  Reply # 1244125 22-Feb-2015 14:08
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The AM300 is a cool little device but it's rather old now, probably discontinued and the half bridge is a bit of a hack.

These days you can get a Draytek Vigor 120 which will do a PPPoA to PPPoE relay/conversion so you can just use a PPPoE client in the 2nd router, so I would just do that.


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  Reply # 1244134 22-Feb-2015 14:37
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Ragnor: The AM300 is a cool little device but it's rather old now, probably discontinued and the half bridge is a bit of a hack.

These days you can get a Draytek Vigor 120 which will do a PPPoA to PPPoE relay/conversion so you can just use a PPPoE client in the 2nd router, so I would just do that.

Or just go with an ISP that supports native PPPoE which eliminates the PPPoE to PPPoA conversion and then the ISAM converting this back from PPPoA to PPPoE to pass thru to the ISP.

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