RuggedCom RuggedRouter RX1100 - Manual (Page 95)

11. Configuring PPPoE/Bridged Mode On ADSL
Revision 1.14.3 95 RX1000/RX1100™
addresses of the ISPs DNS servers to the router. You should use these DNS servers unless you wish
to provide your own.
You will obtain either a dynamic or static IP from your ISP. Firewall configuration should be performed
as is appropriate.
11.1.2.2. PPPoE MTU Issues
The use of PPPoE introduces a limitation of the maximum length of packets. The maximum Ethernet
frame is 1518 bytes long. 14 bytes are consumed by the header, and 4 by the frame-check sequence,
leaving 1500 bytes for the payload. For this reason, the Maximum Transmission Unit (MTU) of an
Ethernet interface is usually 1500 bytes.
This is the largest IP datagram which can be transmitted over the interface without fragmentation.
PPPoE adds another six bytes of overhead, and the PPP protocol field consumes two bytes, leaving
1492 bytes for the IP datagram. This reduces the MTU of PPPoE interfaces to 1492 bytes.
Packets received by hosts via Ethernet that are sized to the Ethernet MTU will be too large for the
PPPoE connections MTU and will be fragmented. Large packets from hosts on the Internet will be
fragmented by the ISP. The router will re-assemble these packets, but at the cost of increased latency.
Configuring smaller MTUs at your hosts may reduce latency.
11.1.2.3. Bridged Mode
In bridged mode, the router simply employs the ADSL interface as a carrier of Ethernet frames. The
interface will be created at boot time with a 1500 byte MTU.
No authentication information is required for bridged mode.
Your ISP will provide you with one or more IP addresses and an appropriate subnet mask. Your ISP
will also suggest a DNS server which you can configure via the Networking, Network Configuration,
DNS Client menu.
11.1.2.4. Location Of Interfaces And Labeling
Unlike the Ethernet ports (which are statically located), the location of ADSL ports in your router
depends upon the number of ports and how they were ordered. Refer to the labeled hardware image
as presented in the Webmin home page.
To make labeling easy to understand, all T1E1, T3, DDS and ADSL ports are assigned a unique port
number that relates to the LEDs on the status panel.
11.1.2.5. LED Designations
The RuggedRouter includes two sources of LED indicated information about ADSL lines, the ADSL
card itself and the LED Panel.
Four LEDs are associated with the line, next to the interface jack.
Power (Green) indicates when the card is active and powered.