Simple Transparent P2P Bridge RB411 <--> RB411

RouterOS Wireless Networking
1

My experience with transparent layer 2 bridges is that they forward packets between interfaces and get out of the way. I can’t find instructions on setting up a simple wireless bridge between two RB411s. The wiki instructions all use additional protocols like WDS, EoIP, MPLS, and others. Are these necessary? Is my understanding over simplified?

I want a simple wireless bridge to connect a PC to a wired network like this:

remote PC <--ethernet--> RB411/XR9 <---wireless---> RB411/XR9 <--ethernet--> Network switch
(remote radio is "station" and local radio is "bridge"

I want the radio interfaces to function transparently as a bridge (wlan1 to wlan1), so I setup one device as “bridge” and the other apparently needs to be setup as “station” to connect. I then created network bridges in both routerboards to bridge ether1 and wlan1. The wlan interfaces do not have IP addresses assigned and the ether1 interfaces have IP addresses assigned as 10.10.10.1 and 10.10.10.2.

This configuration is passing some traffic because WinBox can see both routerboards when running from either side. But it does not appear to be sending all the packets as a transparent layer 2 bridge should. For example, arp -a on the remote PC only shows the local radio, not the remote radio, and I cannot ping across the link from either direction.

Can someone offer some insight please?

Thanks,

Wayne Sherman

2

I would like the bridge(s) to be truly transparent, i.e. pass all packets unmodified so that this:

remote PC <--ethernet--> RB411/XR9 <---wireless---> RB411/XR9 <--ethernet--> Network switch

is equivalent to this:

remote PC <--ethernet--> Network switch

Any help would be truly appreciated.

Thanks,

Wayne

3

The most simple is to use wds.

This has to do with the way that the packet header is built for 802.11

When 802.11 was designed, it was only for wifi clients (laptops, pda, etc…)

When a laptop transmits (equal to mikrotik station mode), the header is built with 3 mac address.

laptop(1mac)->AP(2mac)->destination PC(3mac)

If you want to do a wireless bridge, you will need 4 mac.

This is wds mode, the header has 4 mac address.

SendingPC(1mac)->stationWDS(2mac)->AP(3mac)->destinationPC(4mac).

Google about how the frame for 802.11 is built and it will be easier to understand.

Best regards

4

i tried several setting for my earlier post with station mode client and AP bridge with or without wds but could not succeed in Transparent mode.

However using station-wds and enabling wds bridge on the client side helped me. But I am still looking for a way to make it function without using wds

5

@Jorge: Thanks for the additional information, I will experiment with WDS mode.

Also, in my tests I got a wireless bridge working using “station pseudobridge clone” mode.
Which mode (wds or pseudobridge clone) is preferred for a bridge?
How do these two modes compare in regards to:

  • Performance?
    Compatibility with network topologies?
    Limitations?

@mahnet: I found this information:

http://www.linuxfoundation.org/collaborate/workgroups/networking/bridge

  • …
    What can be bridged?
    Linux bridging is very flexible; the LAN’s can be either traditional Ethernet device’s, or pseudo-devices such as PPP, VPN’s or VLAN’s. The only restrictions are that the devices:

  • All devices share the same maximum packet size (MTU). The bridge doesn’t fragment packets.

  • Devices must look like Ethernet. i.e have 6 byte source and destination address.
    *** Support promiscuous operation. The bridge needs to be able to receive all network traffic, not just traffic destined for its own address.**
    *** Allow source address spoofing. The bridge must be able to send data over network as if it came from another host.**"

…
“It doesn’t work with my Wireless card!”:

“This is a known problem, and it is not caused by the bridge code. Many wireless cards don’t allow spoofing of the source address. It is a firmware restriction with some chipsets. You might find some information in the bridge mailing list archives to help.”
…
“I still don’t understand!!”
Doing full bridging of wireless (802.11) requires supporting WDS . The current implementation doesn’t do it.

It is possible to do limited wireless to Ethernet functionality with some wireless drivers. This requires the device to be able to support a different sender address and source address. That is what WDS provides.

There are ways to make it work, but it is not always straightforward and you probably won’t get it right without a pretty solid understanding of 802.11, it’s modes, and the frame header format."

Thanks,

Wayne

6

Hi,

Did you try this configuration?
http://wiki.mikrotik.com/wiki/Transparently_Bridge_two_Networks_using_MPLS

Regards, Grzegorz.

7

Did you try this configuration? …(MPLS)

No, I haven’t tried it, but I did notice this statement on that page:

  • “802.11n speed is limited over WDS bridges, this method doesn’t have such limitations”

I don’t understand why bridging with WDS would limit the speed. Does anyone have more information about that?

Thanks,

Wayne

8

No, I haven’t tried it

So try it…

I don’t understand why bridging with WDS would limit the speed.

http://en.wikipedia.org/wiki/Wireless_Distribution_System#Technical

Regards, Grzegorz.

9

from the Wikipedia article:

Two disadvantages to using WDS are:

  • The maximum wireless effective throughput is halved after the first retransmission (hop) that is made…
  • Dynamically assigned and rotated encryption keys are usually not supported in a WDS connection…

That is enough for me to not want to use it or waste my time testing it. I may use “station pseudobridge clone” mode on this first install to give me time to read over and test the MPLS config.

I appreciate your guidance.

Thanks,

Wayne

10

WDS does not support Frame Aggregation used by 802.11N. In reality I found this not to make too much difference unless you are getting really good speeds on the N link. We have seen field performance of 65mbps+ using WDS bridging.

On the other hand the MPLS/VPLS bridge is very easy to setup since it does not require additional routing protocols (eg OSPF) on the PTP link. It also appears to put very little additional strain on the router, so I would likely use it in most situations.

11

wds actually kills the link i was getting a charming 65 Mbps HT/65 Mbps HT with “n” enabled and a Pthroughput of 58000 kbps and 106/93 % CCQ but enabling wds and adding 3 stations to my AP ruined and on some links the Pthroughput at times goes down to 200 kbps