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marieL
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Best practice with pppoe+MTU

Mon Sep 22, 2008 6:01 pm

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 ?
 
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parrini
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Re: Best practice with pppoe+MTU

Mon Sep 22, 2008 10:31 pm

Well, I have asked this before here, without success. I use 1480 on the PPPoE server profile. Apparently everything is working fine.
 
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marieL
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Re: Best practice with pppoe+MTU

Tue Sep 23, 2008 10:19 am

Thanks parrini.
1480 for both MTU and MRU ?

M.
 
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mrz
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Re: Best practice with pppoe+MTU

Tue Sep 23, 2008 11:16 am

Default MTU MRU values (1480) are optimal values that will suite in most of cases.
 
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marieL
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Re: Best practice with pppoe+MTU

Tue Sep 23, 2008 2:23 pm

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
 
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parrini
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Re: Best practice with pppoe+MTU

Tue Sep 23, 2008 3:01 pm

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).
 
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marieL
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Re: Best practice with pppoe+MTU

Tue Sep 23, 2008 3:04 pm

thanks parrini.
I will take a look
 
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fatonk
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Re: Best practice with pppoe+MTU

Tue Sep 23, 2008 3:37 pm

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
 
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marieL
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Re: Best practice with pppoe+MTU

Tue Sep 23, 2008 4:58 pm

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
 
rafa_lore
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Re: Best practice with pppoe+MTU

Tue Sep 23, 2008 5:24 pm

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
 
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dibatech
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Re: Best practice with pppoe+MTU

Wed Sep 24, 2008 12:54 pm

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.
 
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macgaiver
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Re: Best practice with pppoe+MTU

Wed Sep 24, 2008 2:24 pm

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.
With great knowledge comes great responsibility, because of ability to recognize id... incompetent people much faster.
 
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marieL
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Re: Best practice with pppoe+MTU

Wed Sep 24, 2008 3:37 pm

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
 
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Re: Best practice with pppoe+MTU

Wed Sep 24, 2008 6:05 pm

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.
 
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amt
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Re: Best practice with pppoe+MTU

Tue Jun 07, 2016 12:14 pm

can use auto mtu for ppoe server and eoip tunnel ?
 
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simeitg
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Re: Best practice with pppoe+MTU

Sun Jul 30, 2017 1:27 am

Why every CCR show 1480 MTU if you create a pppoe-server? Why not 1492 or 1500?
 
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amt
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Re: Best practice with pppoe+MTU

Mon Jul 31, 2017 11:18 am

Why every CCR show 1480 MTU if you create a pppoe-server? Why not 1492 or 1500?
yep Im thinking same thing.
 
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simeitg
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Re: Best practice with pppoe+MTU

Mon Jul 31, 2017 10:49 pm

A friend said that is 1480 to avoid fragmentation.

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