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What is the maximum packet size supported by PPPoE?
1492 bytes
Product and Release Support For a PPPoE interface, the PPPoE header uses 6 bytes and the PPP protocol ID uses 2 bytes. This restricts the maximum receive unit (MRU) size on a PPPoE interface to 1492 bytes, which can cause frequent fragmentation and reassembly of larger PPP packets received over the PPPoE interface.
Is MTU and MRU same?
Typically, the MTU and MRU sizes for a particular network are the same values. For example, Ethernet networks have an MTU/MRU of 1500 bytes, and both of these values are fixed. However, many dial-up networks allow an endpoint system to define different MTU and MRU sizes.
Why is PPPoE MTU 1492?
With PPPoE connections, the PPP and PPPoE header increases the frame size by 8 bytes, so we must lower the MTU to 1492. With the ethernet header added to this, we get a frame size of 1518 bytes. The network between the DSL multiplexer and the ISP aggregation router is ATM.
How big of a MTU do I need for PPPoE?
The maximum MTU of an interface will depend on the hardware platform, but the IEEE 802.3 standards require a minimum MTU of 1500 bytes. PPPoE needs additional 8 bytes and truncates the Ethernet MTU to 1492, and if the effective MTU on the hosts is not changed, the router in between the host and the server can terminate the TCP sessions.
How to figure out the MSS for PPPoE?
The solution for this is called MSS clamping. You use your firewall to override the Maximum Segment Size (MSS) option on all TCP connections so they do not have issues with packets being too large. To figure out the MSS you want, you take the standard 1500 MTU and subtract the PPPoE header, the IP header,…
Is the configuration of MTU and Mru supported?
The configuration of MRU and MTU is supported for subscribers of the following PPP connections: PPP over Ethernet over ATM (PPPoE over ATM) subscribers PPP essentially negotiates between two independent half-duplex links.
Which is the MTU for the TCP MSS?
After some experimenting and reading Wikipedia, I now am confident in 1492 as the MTU and 1452 for the TCP MSS, and I understand why they work. Ethernet frame headers start at 18 bytes long, grow to 22 bytes with VLAN tagging, and 26 bytes with Q-in-Q VLAN tagging.