Hi guys,

I have a problem with setting up my RB2011UAS. I try to connect PPPoE which is working however I am losing 20% of packets.

I tired to play with MTU and when I setup 512 I got nice ping but I still was losing packets.


MTU 1400



And when my modem does authentication for PPPoE:


This means that something is wrong with my settings.
I also checked on my modem that when it does authentication MTU is 1480 and MSS is 1400.

How I can change MSS in Mikrotik? Any other suggestions?

Luca

You can use a firewall-mangle rule to change the MSS but since MSS is specific to the TCP protocol and you are experiencing issues with packet loss when using ICMP, I'm doubtful that this will solve your problem.

Could you provide more insight into your setup? What type of access are you using (ADSL(2/2+), VDSL(2))? What type of modem are you using?

Hi Lenart,

My setup:
PPPoE ADSL2+
VPI: 8
VCi: 35
LLC

I tried to play with firewall command to change MSS: no success.

Any changes to MMS using the mangle rule won't affect ICMP messages as they rarely grow to a size where they are dropped because they are to big. That makes it more likely that the cause of the packet drop is something else.

I have a RB2011UiAS-2HnD hooked up to an ADSL2+ link via a Draytek Vigor 130 that is setup as a bridge (often called "set in bridge mode").
I happen to know that my ISP wraps a PPPoE session in something that Draytek seems to label as 1483 Bridged IP LLC so I set my modem to that setting. This prevents the Draytek Vigor 130 from attempting to login using PPPoE (something that other people reported as a potential issue with Drayteks in bridge mode). As a result, I can see my ISP's PPPoE server when I use the PPPoE scan feature in Mikrotik.

While I understand why you would suspect MTU as the culprit for connection issues, I'm not sure whether your initial analysis here is correct. It would be helpful to get more information about your modem and it's capabilities and settings. I would also advise you to try alternative modems (I've had good experiences with Drayteks and the Vigor 120, which is an ADSL2+ only modem, is relatively cheap, 50-75 euro if I remember correctly).
It could also help to provide some log outputs for the PPPoE filter () to see if there is something that jumps out as the cause. If you get the feeling that the log messages are hard to understand, feel free to post (an excerpt of) the log in the forum.

Furthermore, it would be helpful if you could post the relevant parts of your config so it can be examined.

I already tested two modems. The same result, when they are in bridge mode my router has problems.

I will give you more information soon.

Hi there,

Here are couple of ideas:
*Check cabling ( MT - modem), maybe cable is damaged
*Try to ping some local IP ( if your provider is not blocking ICMP to default gateway obitained by PPPoE), because maybe your provider is having some heavy load on upstream ( ICMP is treated as lowest priority traffic)
* Set MTU to 1492/1480b and then try to ping some IP with DF flag, so you can determine whats your optimal MTU ( 1492+8b PPPoE overhead should be 1500 in total wich is common on ADSL setup), and some ISP's are forcing MTU to 1480.
note: if you are doing this from windows do not forget to remove 28b (20b of IP + 8b of ICMP header)
Also, you can run a traceroute from your MT, and there you can get clearer picture on where packets are dropped.

*Check cabling ( MT - modem), maybe cable is damaged

If this was the root cause, you would expect the issue to exist if the modem is doing the PPPoE authentication. This doesn't seem to be the case though.

*Try to ping some local IP ( if your provider is not blocking ICMP to default gateway obitained by PPPoE), because maybe your provider is having some heavy load on upstream ( ICMP is treated as lowest priority traffic)

This could be a root cause. I guess it would depend on the reliability of the internet access. I personally never have this issue but I happen to live in a country that is host to some large internet exchanges.

* Set MTU to 1492/1480b and then try to ping some IP with DF flag, so you can determine whats your optimal MTU ( 1492+8b PPPoE overhead should be 1500 in total wich is common on ADSL setup), and some ISP's are forcing MTU to 1480.
note: if you are doing this from windows do not forget to remove 28b (20b of IP + 8b of ICMP header)

OP has used several different MTU's so stretching the MTU beyond the provider-suggested 1480 is unlikely to yield better results. It might be a good idea to select an MTU and leave it for a significant amount of time. I would advise 1472 in this case.

Also, you can run a traceroute from your MT, and there you can get clearer picture on where packets are dropped.

A very good idea, it would shed some light on this issue. I do suspect that this could be hit and miss as it seems that there is some connectivity when the Mikrotik is used as the PPPoE client.

I would setup logging that tracks the PPPoE client to see if any ICMP drops coincide with PPPoE log messages.

*Check cabling ( MT - modem), maybe cable is damaged

If this was the root cause, you would expect the issue to exist if the modem is doing the PPPoE authentication. This doesn't seem to be the case though.

It was a blind guess, we have no information about cabling

* Set MTU to 1492/1480b and then try to ping some IP with DF flag, so you can determine whats your optimal MTU ( 1492+8b PPPoE overhead should be 1500 in total wich is common on ADSL setup), and some ISP's are forcing MTU to 1480.
note: if you are doing this from windows do not forget to remove 28b (20b of IP + 8b of ICMP header)

OP has used several different MTU's so stretching the MTU beyond the provider-suggested 1480 is unlikely to yield better results. It might be a good idea to select an MTU and leave it for a significant amount of time. I would advise 1472 in this case.

I have skipped this in OP's post, i'm guilty without any excuse and your hint is really good

I would setup logging that tracks the PPPoE client to see if any ICMP drops coincide with PPPoE log messages.

Agree 100% on this idea.

Thanks guys I will can play with my router tomorrow.