WMM and PPPoE incompatibility?

BrianHiggins · Tue Sep 11, 2007 2:21 am

the addition of WMM to ROS is a great step forward, however I am trying to figure out if it actually benifits those of us who are using PPPoE or not. As I understand it WMM looks at the TCP TOS field to prioritize the delivery of packets via wireless so that higher priority traffic (VoIP, VPN, Etc...) gets deliverd first to help minimize latency and throughput.

BUT...

when you use PPPoE all the traffic is encapsulated inside the PPPoE tunnel as it travels over the wireless link, and therefore the radio never sees the encapsulated TOS field, only the "Host" TOS Field, and therefore all frames are treated as equal priority, despite the fact that some of the actual payload may be of higher priority then normal.

While I understand that there is no way that MikroTik can prioritize traffic from the client over the wireless link via WMM if it is not a MikroTik PPPoE Client, Is there any way for the PPPoE Server (and client) to pass along the TCP TOS field for traffic it is encapsulating and sending from the regular ethernet segment to the other side of the PPPoE link.

Below is a simple network diagram outlining how I beleive it currently works. What I would like to see is that the PPPoE Packet that gets transmitted from the PPPoE Server has the same TCP TOS as the encapsulated packet that is inside of it, instead of being reset to the default of 0

kabelfrei · Tue Sep 11, 2007 9:02 am

very interesting question!!!

warwick09 · Tue Sep 11, 2007 9:32 am

Interesting question indeed but due to the very nature of Pppoe itself there is currently no way WMM and Pppoe can be used in tandom. I.e. Mikrotik cannot peer into a pppoe encapsulated packet and find out its TOS value, furthermore Mikrotik cannot inject' a tos value into the pppoe encapsulated packet itself unless of course they are willing to refine an industry standard ....

Regards

rpingar · Tue Sep 11, 2007 10:26 am

reading the wiki about wmm seems it is possible.

From the pppoe concentrator point of view you are able to mark the priority and then inject the pppoe packet with priority.

from the cpe in bridge mode, you need an ata voip able to mangle the cos and it is commonly done by a lot of ata.

I have never tested this configuration but seems possible.

Ros

rpingar · Tue Sep 11, 2007 10:37 am

If I use eoip tunnel from pppoe concentrator to ap do I need also VLANs like explainde below?

from wiki:

PPPoE server -> WMM AP -> client,

if AP is just forwarding PPPoE traffic (therefore inspecting encapsulated IP packets to match e.g. by protocol is not possible, as packets can be encrypted and compressed), priority must come to AP from PPPoE server in VLAN tag, so you have to use VLAN (between PPPoE server and AP) for this, just to communicate priority information.

Note that you do not have to forward VLAN encapsulated traffic to client - VLAN can be terminated at AP, VLAN tag is needed only when entering AP.

In case AP is PPPoE server itself, there is no need to use VLAN - priority can be set by rules before it is encapsulated in PPPoE.

-----------------------------------------------------

BrianHiggins · Wed Sep 12, 2007 2:01 am

Mikrotik cannot peer into a pppoe encapsulated packet and find out its TOS value

understood and agreed, unless mikrotik is generating the PPPoE encapsulating packet, and then only at the point it is encapsulating it (i.e. the PPPoE client or server it's self)

furthermore Mikrotik cannot inject' a tos value into the pppoe encapsulated packet

I'm not familiar with the exact structure of the PPPoE Frame, but is there no at least 1 or 2 bits that can be used for storing some type of TOS value that the WMM can use to priortize the traffic?

itself unless of course they are willing to refine an industry standard ....

that just depends on the PPPoE frame structure, and if there is any place it can set 2 bits of data (I think that 2 bits to give four levels of priority would be enough, 00, 01, 11, 10)

Alternativly, the vlan tag could be used, but not all people bridge the wireless interface to a VLAN so it would limit the number of people that could benefit from this setup, so if there is a way to tag the PPPoE frame that would be more universal.

Wed Sep 12, 2007 2:58 pm

Priority can not get set in PPPoE frames, therefore other means have to be
used. One approach - communicate priority using VLAN is given as example in
Wiki. Also as Wiki page states:

"you do not have to forward VLAN encapsulated traffic to client - VLAN can be
terminated at AP, VLAN tag is needed only when entering AP."

this means that you do not have to _bridge_ wireless with VLAN, only thing
that matters is getting the priority info to AP (in this case with VLAN
header), later packet can be bridged or routed.

In case EoIP is used, currently there are no means to set DSCP field in EoIP
IP header from priority assigned to packet (which would be the essential way
of maintaining priority of packet over different encapsulations), so
currently VLAN needs to be used.

Another important thing to take into account is that if compression or
encryption is used for PPPoE connection, in order delivery of frames is
required - packets _must_ arrive at PPPoE endpoint in the same order they got
sent from sending side. Taking into account that WMM can reorder packets
based on their priority, use of WMM for encrypted/compressed PPPoE links will
only make things worse - out of order packets will get dropped. And even if
they were kept to ensure order, whole benefit of WMM would be lost.

rpingar · Wed Sep 12, 2007 3:20 pm

may we have into the wiki an exemple on how to configure WMM working on an actual design that use eoip on a reouted network to link all the aps to one PPPoE concentrator?

regards
Ros

rpingar · Wed Sep 12, 2007 3:24 pm

another question is: how to check if the ap is getting priority and using WMM?
is there a way to get wmm statistics?

Regards

BrianHiggins · Wed Sep 12, 2007 7:32 pm

Priority can not get set in PPPoE frames, therefore other means have to be
used. One approach - communicate priority using VLAN...

ok, sounds like an acceptable solution for those of us wanting to implement it

Another important thing to take into account is that if compression or
encryption is used for PPPoE connection, in order delivery of frames is
required - packets _must_ arrive at PPPoE endpoint in the same order they got
sent from sending side. Taking into account that WMM can reorder packets
based on their priority, use of WMM for encrypted/compressed PPPoE links will
only make things worse - out of order packets will get dropped. And even if
they were kept to ensure order, whole benefit of WMM would be lost.

so for any session that uses encryption or compression, any form of prioritization would have to be foregone.

given the following scenerio with a PPPoE server running on the VLAN interface, passing traffic to the AP across to the corresponding VLAN interface on the AP (as shown in my diagram)

/ interface pppoe-server server 
add service-name="IN-LAFA-DWTN-2" interface=vlan2 max-mtu=1488 max-mru=1488 \
    authentication=pap,chap,mschap1,mschap2 keepalive-timeout=10 \
    one-session-per-host=yes max-sessions=0 default-profile=IN-LAFA-DWTN \
    disabled=no

any TCP packet that comes in to the router with a TOS of 16, and exits as a non-encrypted/non-compressed PPPoE Frame on vlan2 SHOULD be tagged as high priority following the 802.1P standard, which SHOULD be read by WMM and transmitted before a regular, normal priority frame would be sent over the wireless link.

therefore the question is: does MikroTik implement 802.1P, and does the WMM implementation use 802.1P to determine prioritization, and does the PPPoE server pass along the TOS value into the 802.1P User Priority field?

BrianHiggins · Wed Sep 12, 2007 7:36 pm

I'm not familiar with the exact structure of the PPPoE Frame, but is there no at least 1 or 2 bits that can be used for storing some type of TOS value that the WMM can use to priortize the traffic?

after some looking into it, in case anyone was wondering, there is no place that I could find that it could be done, therefore as already stated, the VLAN tag would be the only way.

Thu Sep 13, 2007 12:00 pm

As WMM page in wiki already states:

"Priority of packets can be set using "set priority" action of ip firewall
mangle rules and/or bridge firewall filter rules. Priority can be set to
specific value or to "ingress priority". Ingress priority is priority value
that was detected on incoming packet, if available. Currently there are 2
sources of ingress priority - priority in VLAN header and priority from WMM
packets received over wireless interface. For all other packets ingress
priority is 0.

Note that ingress priority value is not automatically copied to priority
value, correct rule needs to be set up to do this! "

and:

"if it is not possible or wanted to classify packets by rules, configuration
of network must be such that router can extract ingress priority from
incoming frames. Remember there are currently 2 sources for this - VLAN tag
in packets and received WMM packets."

So this means that for "PPPoE server on VLAN in EoIP" case, when IP packet
comes into router (to be forwarded to PPPoE client), its "ingress-priority"
is most likely 0 (as already said - "there are 2 sources of ingress
priority" - VLAN and WMM), and priority - 0. In this case mangle rules have
to be used to set priority (e.g. matching by TOS value). Then packet gets
encapsulated in PPPoE, next in VLAN (which sets priority field in VLAN header
from priority set for packet with mangle rule), next in EoIP. So packet looks
like this:
<EoIP header><ethernet header><VLAN header(with priority)><PPPoE header><PPP
header><IP packet>

When EoIP packet gets received at AP, it is decapsulated and when received
over VLAN interface (after EoIP header is stripped off), its ingress-priority
gets set from priority in VLAN header.

To be able to pass this ingress-priority to be used by wireless WMM, it needs
to be copied to priority of packet by mangle rule
(new-priority=from-ingress).

So on PPPoE server add mangle rule:
dscp=16 new-priority=7 (assuming that dscp=16 are voice packets)

On AP add rule (in bridge firewall, as VLAN is bridged with wireless):
new-priority=from-ingress

BrianHiggins · Thu Sep 13, 2007 8:15 pm

To be able to pass this ingress-priority to be used by wireless WMM, it needs
to be copied to priority of packet by mangle rule
(new-priority=from-ingress).

So on PPPoE server add mangle rule:
dscp=16 new-priority=7 (assuming that dscp=16 are voice packets)

On AP add rule (in bridge firewall, as VLAN is bridged with wireless):
new-priority=from-ingress

Can you post (either here or on the Wiki) some example config's of how to set this up both at the PPPoE server, and at the AP? I am having trouble following your descriptions on how you would configure the bridge and mangle rules to set this up, and some config examples would help greatly.

rpingar · Sun Nov 04, 2007 11:39 am

As WMM page in wiki already states:

"Priority of packets can be set using "set priority" action of ip firewall
mangle rules and/or bridge firewall filter rules. Priority can be set to
specific value or to "ingress priority". Ingress priority is priority value
that was detected on incoming packet, if available. Currently there are 2
sources of ingress priority - priority in VLAN header and priority from WMM
packets received over wireless interface. For all other packets ingress
priority is 0.

Note that ingress priority value is not automatically copied to priority
value, correct rule needs to be set up to do this! "

and:

"if it is not possible or wanted to classify packets by rules, configuration
of network must be such that router can extract ingress priority from
incoming frames. Remember there are currently 2 sources for this - VLAN tag
in packets and received WMM packets."

So this means that for "PPPoE server on VLAN in EoIP" case, when IP packet
comes into router (to be forwarded to PPPoE client), its "ingress-priority"
is most likely 0 (as already said - "there are 2 sources of ingress
priority" - VLAN and WMM), and priority - 0. In this case mangle rules have
to be used to set priority (e.g. matching by TOS value). Then packet gets
encapsulated in PPPoE, next in VLAN (which sets priority field in VLAN header
from priority set for packet with mangle rule), next in EoIP. So packet looks
like this:
<EoIP header><ethernet header><VLAN header(with priority)><PPPoE header><PPP
header><IP packet>

When EoIP packet gets received at AP, it is decapsulated and when received
over VLAN interface (after EoIP header is stripped off), its ingress-priority
gets set from priority in VLAN header.

To be able to pass this ingress-priority to be used by wireless WMM, it needs
to be copied to priority of packet by mangle rule
(new-priority=from-ingress).

So on PPPoE server add mangle rule:
dscp=16 new-priority=7 (assuming that dscp=16 are voice packets)

On AP add rule (in bridge firewall, as VLAN is bridged with wireless):
new-priority=from-ingress

Ok i was able to configure my network as you described. I have an AP where the vlan is bridged with wlan1.
But now using nstream I can't use wmm. And so I would like to use queue to achive a comparable result.
I set ingress-priority on bridge firewall.
Then I would like to mark packet to build a queue tree. But I am not able to mark packet based on priority..........

How to get this done?

Regards
Ros

BrianHiggins · Mon Nov 05, 2007 7:09 pm

Ok i was able to configure my network as you described. I have an AP where the vlan is bridged with wlan1.
But now using nstream I can't use wmm. And so I would like to use queue to achive a comparable result.
I set ingress-priority on bridge firewall.
Then I would like to mark packet to build a queue tree. But I am not able to mark packet based on priority..........

How to get this done?

Regards
Ros

adding simple queue's to the wireless interface is not the same as QOS, all you are doing is providing a fixed bandwidth allocation to certain types of traffic, not ensureing the traffic gets there first. The real solution is for MT to add a WMM version designed to work with NStream (http://forum.mikrotik.com/viewtopic.php ... 003&hilit=)

That said, I haven't tried this in production, but how about this?

/ interface bridge filter 
add chain=forward action=mark-packet new-packet-mark=priority7 \
    in-interface=vlan1 mac-protocol=vlan vlan-priority=7 comment="" \
    disabled=no

rpingar · Mon Nov 05, 2007 9:46 pm

Ok i was able to configure my network as you described. I have an AP where the vlan is bridged with wlan1.
But now using nstream I can't use wmm. And so I would like to use queue to achive a comparable result.
I set ingress-priority on bridge firewall.
Then I would like to mark packet to build a queue tree. But I am not able to mark packet based on priority..........

How to get this done?

Regards
Ros
adding simple queue's to the wireless interface is not the same as QOS, all you are doing is providing a fixed bandwidth allocation to certain types of traffic, not ensureing the traffic gets there first. The real solution is for MT to add a WMM version designed to work with NStream (http://forum.mikrotik.com/viewtopic.php ... 003&hilit=)

That said, I haven't tried this in production, but how about this?
Code: Select all
/ interface bridge filter 
add chain=forward action=mark-packet new-packet-mark=priority7 \
    in-interface=vlan1 mac-protocol=vlan vlan-priority=7 comment="" \
    disabled=no 

I did it, but it didn't get the job done. It is not working as expected.

I think there could be abug inside the bridge filter about vlan mac-protocoll

regards
Ros

BrianHiggins · Mon Nov 05, 2007 10:00 pm

i created that rule on a 2.9.48 spare radio on a tower, so I have no way to test to see if it does anything or not.

WMM and PPPoE incompatibility?

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