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Tommo
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Joined: Mon Dec 04, 2017 10:35 pm

MTU on VLAN with VRRP Help!

Mon Dec 04, 2017 10:45 pm

So I have setup two mikrotiks running VLANS, on top of VRRP, on top of bonded interfaces. I am doing this because I have more VLANs than interfaces that I want to get higher aggregated interface throughput. All is working OK but I am having weird MTU issues. I have gone through the various posts regarding MTU and L2MTU calculations but no values I set seem to work. I cant find any post in this configuration to determine if the VRRP config also alters the attached packet size or not.

So the setup looks like this
-> Eth1, Eth2, Eth3 Bonded
--> VRRP established and working on bond
----> VLAN configured on VRRP interface
------> IP address configured on VLAN interface
------> Second IP address configured on second VLAN interface
---------> Routing between the two VLAN interfaces

With all MTU set at the default 1500 I get a lot of broken packets and connection timeouts, as I lower this on the VLAN interface much of this is resolved but I still get a lot of connections failing to respond.

EDIT-----
This started working briefly, when it did the L2 MTU values all changed by themselves to the correct ones, and everything was fine, disabled and re-enabled the bonded interface and everything set back to the default 1500 values and it all broke again. Could this be MTU path discovery not working? Or is there something else which sets the L2 MTU?

When working all the MTU values were 1500, and the bonded and vrrp L2MTU was automatically changed to 1510, and the VLAN L2MTUs changed to 1506. I cant work out how to get them back to those values.



Any help would be greatly appreciated!! :D
 
glennyray
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Joined: Sun Feb 25, 2018 7:53 am

Re: MTU on VLAN with VRRP Help!

Mon Feb 26, 2018 12:35 am

Hi,
I have the same problem trying to use jumbo frames but because I can't increase the vrrp mtu i am getting packet fragmentation.
Did you ever find a solution?
Thanks
 
Tommo
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Posts: 2
Joined: Mon Dec 04, 2017 10:35 pm

Re: MTU on VLAN with VRRP Help!

Mon Mar 05, 2018 10:49 pm

No never worked it out, ended up having to use many physical interfaces with many vrrp instances in to VLAN access ports on the switch. Really gives me the shits........

If you work it out I would love to know how, I have just put it down to the hardware I am using, will eventually but a router board and see if that is any different.
 
markmcn
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Joined: Wed Mar 03, 2010 2:15 am

Re: MTU on VLAN with VRRP Help!

Tue Mar 06, 2018 1:07 am

Hi Tommo
If I have read your first post the design you have outlined doesn't make sense
-> Eth1, Eth2, Eth3 Bonded
--> VRRP established and working on bond
----> VLAN configured on VRRP interface
------> IP address configured on VLAN interface
------> Second IP address configured on second VLAN interface
---------> Routing between the two VLAN interfaces
I believe it should be something closer to this

So the setup looks like this
-> Eth1, Eth2, Eth3 Bonded
--> VLAN configured on Bond interface
---> IP address configured on VLAN interface (E.g 10.0.0.3/24) (First Router)
----> VRRP Configured & Built on VLan interface
------> IP address configured on VRRP interface (E.g 10.0.0.1)
Putting a vlan on top of a VRRP interface doesn't make sense as you are building a layer2 interface on a layer3 interface.
I hope this helps. Also depending on the device but most bond interfaces are CPU bound so traffic over the bond will have to hit the CPU and this could result in the CPU being loaded and causing other issues.
Regards
Mark

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