Cisco switches breaking connections between Motorola Routers

[carmellogianino1111]

Hello,

We support a radio network that uses Motorola GGM8000 routers for connecting to the back haul network.  These routers can communicate without issue until we install a Cisco switch in-between the 2 routers at which point the connection breaks.  I have taken an un-managed 4 port Netgear switch, put it between the 2 routers and the connection works without issue however if I put any cisco switch in the middle the connection fails.  I have tried the following in an attempt to make this connection work on various Cisco switch platforms ranging from a 2900 all the way through to a 9404 along with a variety of IOS images to no avail.  I have tried to make the ports access ports, trunk ports, tagged the VLAN, untagged the VLAN, played with speed/duplex Switching, Other Switchingand the connection will not come up.  I would chalk this up to a compatibility issue however we have a production network where this is functioning.  I have obviously mirrored that set up to the best of my ability (this runs across a provider switched network which I can only simulate so much) however despite anything I try, this connection still fails.   I'm not sure if there is maybe some hidden commands that need to be implemented or what at this point?  Any ideas or suggestions would be greatly appreciated!     

[Reza Sharifi]

Hi,

When you use an un-managed 4 port Netgear switch, and it works fine, that means the port on the Cisco switch needs to be an access port. Can you make sure the Cisco switch has the right vlan configured if you are using any other vlan beside vlan1? If you are using the default vlan (vlan1) than there is no need for any config on the port. Also, on the Cisco switch, can you configure the port with right speed and duplex as there maybe a mismatch? Does the physical port comes up when connecting to the Cisco switch or no light at all?

HTH

[carmellogianino1111]

I have tried every variation of speed/duplex settings, still no good.   The required VLAN is 288 of which has been configured and the ports in question are set as an access port and still no good.    The switch was "write erased" prior to configuring the 2 ports in question so there is no other configuration on the switch.  What is strange is the face that the interface counters have a ton of input relative to the amount of output.  After clearing the counters there is about 100 packets input for every 1 packet output on each of the interfaces connecting to the 2 Motorola GGM8000 routers .  It appears it is simply not passing the traffic.  

[Reza Sharifi]

Can you put the interfaces connected to Motorola GGM8000 routers in default mode by using this command:

default interface x 

no shut

This will basically turn the switch to a dump hub and it should simply pass traffic between the 2 ports.

Also, can you make sure the VTP mode is transparent?

HTH

[carmellogianino1111]

Thank you for the replies! 

So far I have tried to default the ports like mentioned above, no luck.  I tried making it a trunk with the VLAN in question as both tagged and un-tagged, no luck.  Over the weekend I ended up putting a packet capture on it and it appears it is trying to run BFD through the switch.  I attempted to use the "ip forward protocol" for ports 3874 & 3785, still no luck.  I've also tried to add an additional switch in between (2 switches between the Moto Routers) and encapsulate it in a QnQ layer 2 tunnel , nothing.   Is there something else that I need to enable to let BFD pass through the switch?  I thought it would just let that pass by default?   I'm running out of ideas to try at this point.  Any further help would be really appreciated and thanks again for the help thus far!

[Richard Burts]

I wonder if configuring the switch ports connecting to the routers with portfast might help?

Perhaps the output of show interface for the switch ports might have something helpful?

Perhaps the output of show spanning might have something helpful?

Do the routers show up in the switch mac address tables?

If you have a packet capture it would be interesting to see what frames from the routers look like (what mac addresses, what protocols and ports, etc)

I agree that if the routers work fine when connected to an unmanaged switch that the switch ports should be simple access ports. I see no advantage in any kind of trunking configuration.

[paul driver]

Hello

Wouldnt harm to try and change the cabling and test again.

[Giuseppe Larosa]

Hello @carmellogianino1111 ,

I wonder if the traffic between your routers is IPv4 multicast.

One of the main differences between an unmanaged switch and a Cisco switch is that the last one has IGMP snooping enabled by default.

This can create issues if there is no device that performs IGMP queries and breaks multicast connectivity in the VLAN.

If this is the case you would need to configure an IGMP snooping querier for the VLAN of interest 288.

Hope to help

Giuseppe