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Mike_L__62783's avatar
Mike_L__62783
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Jan 26, 2011

LTM 10.2 - MAC Address Change w/ Different Volume

In trying to apply Hotfix2 for 10.2 tonight we came across a strange issue. We saw the MAC addresses move around between interfaces. For example our external MAC ended in .84 on one volume and in .85 on the other. This caused a network connectivity issue as we had to clear out the ARP cache in order to get things moving. We thought this was strange behavior and were curious if anyone else has seen this or know why it occurs?

 

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  • Chris_Miller's avatar
    Chris_Miller
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    Jan 26, 2011
    Another reason for MAC Masquerading

     

     

    https://support.f5.com/kb/en-us/solutions/public/7000/200/sol7214.html

     

     

    I'm not sure what you mean by "moved around between interfaces." Are you using trunks? I'd expect your ARP entry to be that of your VLAN, not an interface.
  • Mike_L__62783's avatar
    Mike_L__62783
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    Jan 26, 2011
    In the CLI they are the interfaces listed when doing an ifconfig. In the GUI you can call them VLANs. Either way they MAC address moved from one VLAN or interface to another when booting to a different volume.

     

     

     

  • Chris_Miller's avatar
    Chris_Miller
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    Jan 26, 2011
    Posted By Mike L. on 01/26/2011 09:29 AM

     

    In the CLI they are the interfaces listed when doing an ifconfig. In the GUI you can call them VLANs. Either way they MAC address moved from one VLAN or interface to another when booting to a different volume.

     

     

     

     

    So the MAC Address of the VLAN/Interface changed after an upgrade basically?
  • hooleylist's avatar
    hooleylist
    Icon for Cirrostratus rankCirrostratus
    Jan 27, 2011
    I think MAC addresses are assigned from lowest to highest address as each VLAN is created. So if you created VLAN1 and then VLAN2 on one slot, but created VLAN2 then VLAN1 on the second slot, the MAC addresses would be reversed between the two. You can see this on a single slot if you create, delete and then recreate two VLANs in opposite order: 

    
 b vlan VLAN1 {interfaces 2.1}
 b vlan VLAN2 {interfaces 2.2}
 b vlan|grep ^VLAN
VLAN VLAN1   tag 4094   00:017:60:B3:83   MTU 1500
VLAN VLAN2   tag 4093   00:017:60:B3:84   MTU 1500
 b vlan all delete
 b vlan VLAN2 {interfaces 2.2}
 b vlan VLAN1 {interfaces 2.1}
 b vlan|grep ^VLAN
VLAN VLAN1   tag 4093   00:017:60:B3:84   MTU 1500
VLAN VLAN2   tag 4094   00:017:60:B3:83   MTU 1500

    Chris's suggestion of using MAC masquerading should be a good way to avoid this as it allows you to manually specify a custom address to a VLAN or all VLANs on both units.

    Or you could ensure the VLANs are created in the same order. You could also manually clear the ARP tables of neighboring switches to avoid this when booting between slots.

    Aaron