Aggregate Wireless PTP LInks

Posted on 2014-12-29
Last Modified: 2015-02-12
Brief - is it possible to aggregate two wireless PTP links in order to double throughput and potentially reduce latency between locations?

We have two pairs of wireless point to point links (Cambium PTP600) configured from one building to another.  Both pairs are connected to HP Procurve V1910 switches.  On both switches, I've created dynamic bridge aggregation interfaces with two selected ports.  (Possible side note - I have also configured BAGG1 as either Trunk or Hybrid link type with no effect on the connection.)

When I plug the devices into the aggregated ports, the status of both member ports shows as "Selected".  However, the connection still seems to be operating via only one of the two PTP links.  The throughput nor latency are affected (exactly the same as when only one PTP link is connected).  If I pull one of the links, the connection does cut over to the other link after about 30 seconds so there does appear to be fault tolerance.  And lastly when all four Cambium devices are plugged into aggregated switches, I lose HTTP management access to three of the four (and it's restored when I unplug any one of them).

Does it sound as though I am not configuring the switches properly or is there something about wireless PTP links that would prevent them from configuring in the same way wired links would?  Thanks very much in advance!
Question by:pcamis
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LVL 11

Expert Comment

ID: 40521780
Do the Cambium devices support LACP? If so, I think this might be the best way to aggregate those links via the Procurves.
The loss of management access when you have all four devices plugged in is strange, and hints at spanning-tree or some other loop-detection mechanism - although it's hard to tell without more detail.
LVL 50

Expert Comment

by:Don Johnston
ID: 40521895
However, the connection still seems to be operating via only one of the two PTP links.  The throughput nor latency are affected (exactly the same as when only one PTP link is connected).
That would be normal.  When you aggregate two links, traffic from a single flow (an FTP transfer, for example) will use only one of the links.  But other flows could use the other links.

 If I pull one of the links, the connection does cut over to the other link after about 30 seconds so there does appear to be fault tolerance.
That does not sound like you have the trunk setup.  That sounds like spanning-tree behavior.  Which means that all traffic is using only one link.

Can you post the configs of the two switches and indicate which ports are connected to the Cambium devices?

Author Comment

ID: 40522081
Thank you both for your comments.  I am attaching config files for both switches.  The aggregate port in use is BAGG1 which is mapped to 1/0/23 and 1/0/24 (same config on both switches).  The one device that remains controllable is attached to port 1/0/23 of the .202 switch.

@rharland2009 - I believe that the devices do support LACP.  I've attached a couple of excerpted pages from the user guide, but I believe the relevant text is:
The PTP 600 Series is transparent to layer two control protocols (L2CP) including:
• Link aggregation control protocol (LACP)
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LVL 50

Expert Comment

by:Don Johnston
ID: 40522475
I'm not sure what your bridge-aggregation interface is.  Whenever I've done this, I use the trunk command.

For example:

trunk g1/0/1, g1/0/3 trk1 lacp

What do you see when you issue a "show span vlan 617"?  Does it show one of the ports as blocking?

Author Comment

ID: 40522522
Apologies for the following question, but where would I input such commands?  When not using the GUI (my tool of choice), I access the switch via SSH along with the extended command set here:

I've understood that this is a mirror of the commands available when connecting via console port, but are there more via console that I'm not aware of?  Though based on a Google search, those may be Cisco commands and I can't seem to find the HP equivalents.  Thanks again!
LVL 50

Expert Comment

by:Don Johnston
ID: 40522621
I was assuming that the 1910 used the same UI as other HP switches that I've worked on.

But in looking at a manual for the 1910, that doesn't appear to be the case.

According to this document, it looks like configuring a trunk is done through the GUI only (page 226) since they have no mention of the CLI commands used.

Usually (at least on the HP Procurve switches I've configured), anything you can do from the console, you can do over telnet or SSH.  And there are some tasks that can't be done through the GUI and must be done from the CLI.

This switch appears to be the exception.
LVL 46

Accepted Solution

Craig Beck earned 250 total points
ID: 40522995
First thing - you won't reduce latency by aggregating the links.  That just won't happen unless you're saturating your links to start with and need more bandwidth.

The PTP600 does transparently pass LACP traffic so you should be able to form an EtherChannel or Trunk using two radios - however I'd strongly suggest that you don't.

When you create an EtherChannel using wires you are guaranteeing the physical data-rate, but with wireless you're not as the physical data-rate can fluctuate due to a number of factors even though the wired port still shows the same link-speed.  This can cause real problems with EtherChannels and you might see unexpected results if the data-rate fluctuates too much on either wireless link.

I'd go layer-3 if you can - route over each link.  You'll probably find that it works better for you.  If you need to extend a layer-2 segment though this won't be an option and in that case I'd just use STP to manage failover and forget about aggregation.

Author Comment

ID: 40525495
Thanks craigbeck for all of the info - very useful!  I've currently got the PTP600s connected to the switches without utilizing the bridge so that I retain HTTP access to both.  STP is doing it's job as there's no bridge loop and failover is working (albeit after about 30 second delay, which I presume is normal).

Layer 3 is new to me so I apologize for the lack of knowledge here.  I've done some research and understand that it's about IP routes and VLANs.  Could you explain in broad terms how this configuration would work?  I presume I'd set up a new VLAN (different VLANs for both pairs of PTP600's?), assign each switch an additional new IP address within a new subnet, assign the VLAN to the new IP address, then bridge the VLANs at the switch (or router?) level.  With a layer 3 approach, are you suggesting we'll be able to achieve link aggregation (though perhaps not technically termed as such)?

(Side note - since our switches are layer 3 capable, would we see much benefit running even our wired gigabit connections via layer 3 or is the improvement minimal for a small office (~45 people)?)

Thanks very much for your help so far, and to all, a very happy and healthy New Year!
LVL 46

Expert Comment

by:Craig Beck
ID: 40525542
If you're using STP 30s is about right.  You'll be sending traffic over one link only and the other will just be sending BPDUs at intervals.

With Layer-3 links you'd have separate routed links which could be used at the same time.  The advantage of using Layer-3 links is that you're not sending broadcast (unwanted in most cases) traffic over the wireless links which can reduce throughput.  In busy networks this can be a huge problem, especially on large broadcast domains.  If you go Layer-3 you create two separate broadcast domains (one each side of the bridges).

All you'd really need to do is configure two routed interfaces on each switch and connect the bridges.  Each link would be its own /29 (for example to allow for management of the radios too).  You'd have a VLAN (or VLANs) at each side for your clients.

Author Comment

ID: 40537732
I'm following most of the way.  Only piece I'm not 100% sure about in this setup is where the VLANs are set to communicate with each other.  Right now, most of our devices are on VLAN 1.  We also have VLAN 6 setup for IP phone traffic.  All switch ports have untagged membership with 1 and tagged for 6.  Currently the VLANs communicate with each other via two interfaces and policy set on our gateway.

If I create a VLANs for each pair of devices and place them on their own subnets (e.g. VLAN 20 for one pair with subnet 192.168.20.x and VLAN 30 for the other pair with subnet 192.168.30.x), is the link between the VLANs/subnets achieved via IPv4 routing at the switch level?  This is where I get a bit lost - how to tie these new VLANs/subnets back to our existing VLANs.

Again - my apologies for asking these perhaps simple questions.  Learning about networking on the job and have looked for guides, but not found a clear one.  Thanks very much again for the assistance!
LVL 50

Expert Comment

by:Don Johnston
ID: 40537744
The VLANs will not extend over the two sites if you do layer-3 links.  

If you need the same VLANs in both sites, you will need to do layer-2 links.

Author Comment

ID: 40537780
Thanks Don!  Trying to wrap my head around the topology...

Current setup:
Main branch - Data (VLAN 1, Subnet .1.x), Phones (VLAN 6, Subnet .6.x)
Links - Operate/Managed (VLAN 1, Subnet .1.x), transparent to tagged VLAN traffic
Remote branch - Data (VLAN 1, Subnet .1.x), Phones (VLAN 6, Subnet .6.x)

If I understand correctly, you're suggesting that to use Layer 3, we would do this:
Main branch - Data (VLAN 1, Subnet .1.x), Phones (VLAN 6, Subnet .6.x)
Link 1 - Operate/Managed (VLAN 20, Subnet .20.x)
Link 2 - Operate/Managed (VLAN 30, Subnet .30.x)
Remote branch - Data (VLAN 2, Subnet .2.x), Phones (VLAN 7, Subnet .7.x)

I get lost where the VLANs communicate with each other so that traffic on VLAN 2 would speak transparently with VLAN 1.

Again - very sorry for what feel like rudimentary questions.  I don't have much experience with IP Routing so am figuring this stuff out on the fly.  Appreciate very much the help!
LVL 50

Assisted Solution

by:Don Johnston
Don Johnston earned 250 total points
ID: 40537801
Well, I'm not suggesting it. :-)

I'm just saying that if you use layer-3 links to connect the buildings, then you can't have the VLAN's span the two buildings.

If the phones in both buildings don't have to be in the same VLAN, then you're correct. Your proposed topology  (VLAN1-subnet 1.x, VLAN 2-subnet 2.x, etc.) will work.

If, on the other hand, the phones in both buildings have to be on the same VLAN, then you will not be able to connect the two buildings with layer-3 links.

Author Comment

ID: 40538023
OK - now I think I'm following, and if I'm accurate, then Layer 3 may not work for us.  The point of the wireless link setup is that it would serve as close to the same function as running an ethernet cable from the switch in one building to the switch in the other.  We have the two pairs of devices to try to make the connection more robust, with hopes of increasing throughput but at very least reducing congestion over a single link.

All workstations need to be able to access the same set of central servers, and all phones need to be able to contact all other phones.  They don't necessarily need to be on the same VLAN if there is a benefit to this configuration in regard to network quality.  But ultimately, somewhere in the topology, the VLANs WOULD need to communicate with each other, and it sounds like the place to connect VLAN traffic is all the way up at the gateway level.  Do I understand correctly that you can't (or wouldn't want to) connect VLAN traffic at the managed switch level?
LVL 50

Expert Comment

by:Don Johnston
ID: 40538067
It all comes down to whether or not the phones and other devices have to be on the same VLAN.  If they don't, make the inter-building links layer-3.

If they do, then make the links layer-2.

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