Cisco 1720 - Single FA port - PPPoE - MTU issue

[rainman]

I have a C1720 authenticating over my DSL via PPPoE. Everything is working great, except I am unable to pull up specific webpages.

If I install my ISP's PPPoE client on a workstation and build a tunnel in that method, I still have to adjust the MTU on my PC's NIC card to 1428.

I have tried to adjust my "Dialer1" interface to "mtu 1428", but I still can no pull up specific webpages (PNC Bank, and a few others).

I did try putting the "ip mtu 1428" on my FA port but that still didn't make a difference.

Does anybody have any suggestions? The one thing that I noticed is when the router finds interesting traffic and builds out the tunnel, it creates a software interface called "Virtual-Access 1". I even attempted to configure the MTU on this interface but I get the following error:

% Please use virtual template to configure your virtual access

Does anybody have any MTU fixes for the C1720? I really enjoy using this router but the fact I can only pull up specific webpages, I'll have to remove it from ny network if I don't get this resolved.

Any help would be very appreciated.


Tx- Rich

 

[ciup]

Try to see if a smaller (like 1200) MTU for the Dialer1 makes any difference. This way you might narrow the possibilitie on what it might cause that.
Also, you might try to do IP packet debugging on the router and see what exactly happens when you try to connect to those specific websites.

 

[pc2mike]

You must adjust the maximum segment size on the ethernet interface for your local lan (and/or any other internal interfaces)

ie.
interface Ethernet0
ip address 192.168.100.1.255.255.255.0
ip tcp adjust-mss 1452
ip nat inside

Hope this helps,
pc2mike

 

[pc2mike]

P.S. this is on your cisco router only...

 

[ciup]

Here is an article that explains your problem (MTU size for PPPoE) from Cisco and Microsoft.

http://www.azacamis.com/articles/mtu.htm