MikroTik

I must learn how to manage a network of CPE, Point-MultiPoint, Point-Point, Subscriver server, all with Mikrotik and RouterOS.
Point-Multipoint create an EoIP tunnel with subscriver.
All the interfaces of all the network have a MTU=1500.
All the CPE's create a pppoe tunnel with subscriver.

In this case, which is the best MaxMTU and MaxMRU in PPPPOE servers to avoid any problem ?

Well, I have asked this before here, without success. I use 1480 on the PPPoE server profile. Apparently everything is working fine.

Thanks parrini.
1480 for both MTU and MRU ?

M.

Default MTU MRU values (1480) are optimal values that will suite in most of cases.

I suspect somewhere ICMP packet receive a deny.
How can I test the ruter of the network if they correctly notify the sender that a too large packet must be fragmented ?
Wath type of ICMP packet I must allow ?
Now are allower: 0, 3, 4, 8, 11, 12.

Thanks

1480 MTU and MRU. For ICMP you have to choose what you want to pass and take into consideration the direction of the packet. I think your selection is ok, Type 3 Code 4 should take care of fragmentation. Maybe you should also consider Type 30 (Traceroute).

thanks parrini.
I will take a look

You can calculate the MTU, it depends on technology that you use, if you are using only PPPoE you should adjust the MTU at 1480, but if you have after PPPoE some IPIP tunnel or EoIP that will give more overhead, because of new headers etc etc.

Regards.

Faton

Hmmm...
I have pppoe connections inside a EoIP tunnel.
EoIP have MTU=1500.

Eoip attach its header to the pppoe frames (24bytes?); pppoe attach 20bytes to IP frame.

If this is correct, I must:
1. in pppoe servers set MAXMTU and MAXMRU to 1500-24-20 = 1456
2. change the MTU of the public interface to 1456 to publish the correct MTU size

Where am I wrong ?

thanks

Hello
The best MTU you have to find for your networks, Look this page
http://help.expedient.com/broadband/mtu_ping_test.shtml
or
http://www.dslreports.com/faq/5793

Bye
Rafael Lore

I agree. MTU setting of 1456 as well as MRU works well. especially if this network is also supplied connectivity from some pppoe-session / vpn from ISP.

I use MRRU=1520 option and this way was able to avoid any MTU problems without change-mss mangle rules

in windows make sure that - in "networking" tab -> "settings" button -> "Negotiate multi-link over single-link connections" is enabled.

macgaiver,
what is your full MTU configuration ?
I have the real interfaces (eth and wlan) with MTU= 1500, the eoip tunnel with MTU=1500.
Have you the same configuration ?
Which values do you use for MAX MATU and MAX MRU for pppoe server ?

thanks

I played around a bit with wireshark to check on a few things.

Seems like the header on an EoIP tunnel is 42(that includes the 20 byte IP header) bytes, and PPPoE is normally 8 bytes. So its seems like the Eoip MTU should be 1458 and the PPPoE mtu 1450. Though it works fine to use 1500 mtu on the EoIP and 1492 for the PPPoE, it just fragments alot of the packets, putting a little more strain on the router.

can use auto mtu for ppoe server and eoip tunnel ?

Why every CCR show 1480 MTU if you create a pppoe-server? Why not 1492 or 1500?

Why every CCR show 1480 MTU if you create a pppoe-server? Why not 1492 or 1500?

yep Im thinking same thing.

A friend said that is 1480 to avoid fragmentation.