Knowledgebase: VPN and Remote Access
Configuring Vigor2820 to use MTU size of 1500 for PPPoA
Posted by on 15 February 2012 11:06 AM

The steps are:

 

  1. Configure WAN PPPoA and the related settings, click OK.
  2. Telnet to the router and run the following command:

"wan mtu 1500"

 

If you change the WAN PPPoA page, then you will need to re-configure wan MTU again via telnet.

 

Additional Information on PPPoA

Point-to-Point Protocol over ATM (PPPoA) and Point-to-Point Protocol over Ethernet (PPPoE) are two alternative protocols for connecting to your ISP. Some ISPs only support one or the other, but many support both. Additionally, some PCI-based ADSL modems only support PPPoA.

 

PPPoA is ever so slightly faster than PPPoE as PPPoA has 8 fewer bytes of overhead in every 1500 byte packet. Most users do not notice the difference which works out to be about one-half of one percent.

 

Using PPPoA does avoid the Maximum Transfer Unit (MTU) issue. The effect of mismatched MTUs is that random web pages may not load fully, file transfers and email downloads may also appear to freeze. The MTU for PPPoA is 1500 bytes, whereas the MTU for PPPoE is 1492 bytes due to the 8 byte overhead which this protocol incurs. On MS Windows PC(s), the solution for PPPoE MTU issues is usually to lower the MTU on the network interface card (NIC) using one of the various utilities such as DrTcp

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