I have a PPPoE server in a routed network and I would provide full 1500 MTU to pppoe clients and in future I could add some vlans from concentrator to clients, so now I have to setup the various interfaces MTU.
PPPoE adds 8 bytes overhead so interfaces MTU and L2MTU have to be at least 1508, but there are also EoIP and vlans... Anyone can help?
Re: PPPoE at 1500 MTU with EOIP, OSPF and future VLANS
What is your actual question?
Re: PPPoE at 1500 MTU with EOIP, OSPF and future VLANS
Update.
I set the following MTU:
- PPPoE MTU MRU 1500
- VLAN interfaces MTU 1500
- EoIP interfaces MTU 1512 (calculated as 8 byte for pppoe and 4 bytes for vlan)
- Ethernet interfaces MTU 1554 (calculates as 1512 + 42 byte eoip header )
Are they correct?
I set the following MTU:
- PPPoE MTU MRU 1500
- VLAN interfaces MTU 1500
- EoIP interfaces MTU 1512 (calculated as 8 byte for pppoe and 4 bytes for vlan)
- Ethernet interfaces MTU 1554 (calculates as 1512 + 42 byte eoip header )
Are they correct?
Re: PPPoE at 1500 MTU with EOIP, OSPF and future VLANS
Hmm, I thought we had already gone over this before. Are you doing 1500 MTU PPPoE without MRRU *over* the VLANs? Any interface you are running PPPoE over would need to be at least 1508 MTU, including VLANs.
-- Nathan
You tell me. Have you tested it? Does it work? Do you need external validation?Are they correct?
-- Nathan
We had gone over this but there aren't VLAN and EoIP.
The PPPoE won'be over vlan but they are 2 parallels ways to provide some services. I tested it but I'm not sure because the icmp ping works different in routeros and Windows.
If I ping the pppoe server from Windows attached to pppoe client on a rb with pppoe over eoip I can ping without fragmentation with a maximum of 1472. If I ping from rb with pppoe client I can ping without fragmentation with a maximum of 1500 byte.
The PPPoE won'be over vlan but they are 2 parallels ways to provide some services. I tested it but I'm not sure because the icmp ping works different in routeros and Windows.
If I ping the pppoe server from Windows attached to pppoe client on a rb with pppoe over eoip I can ping without fragmentation with a maximum of 1472. If I ping from rb with pppoe client I can ping without fragmentation with a maximum of 1500 byte.
Re: PPPoE at 1500 MTU with EOIP, OSPF and future VLANS
Ah, okay, that's where the confusion is. Yes, Windows treats the "size" parameter for ping differently than other operating systems. As Microsoft documents here, Windows ping size does not include headers, where many other operating systems ping commands do include headers; quoting from the site:I tested it but I'm not sure because the icmp ping works different in routeros and Windows.
20 + 8 = 28, and 1500 - 28 = 1472. So in Windows, when you send pings with size = 1472 bytes, it is actually sending 1500 byte packets, because the 1472 byte size doesn't count the 28 bytes' worth of IP and ICMP headers in each packet sent.Note that the size parameter used by ping is the size of the data buffer to send, not including headers. The ICMP header consumes 8 bytes, and the IP header would normally be 20 bytes.
-- Nathan
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