Creating VRFs steals a VLAN ID

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Feb 25th, 2010
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When I create new VRFs on a 6500 platform i see the following in the log:

.Feb 25 16:33:18.120: %LINEPROTO-5-UPDOWN: Line protocol on Interface VRF_81_vlan1172, changed state to up

The 6500 "steals" a VLAN ID for internal use. This VLAN can then not be used:

6509(config)#vlan 1172

VLAN id: 1172 is an internal vlan id - cannot use it to create a VTP VLAN.


It messes up things because the VLANs seems to be allocated more or less randomly ... In our organisation this range is allocated for other use ...


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Giuseppe Larosa Thu, 02/25/2010 - 10:02
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Hello Jorgen,

what IOS image is running on the C6500?

what VTP mode ?

Hope to help


ansalaza Thu, 02/25/2010 - 10:20
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This might help understand what is going on:

The internal VLANs are allocated in ascending order, starting at VLAN       1006. It is recommended to assign the user VLANs as close to VLAN 4094 as       possible in order to avoid conflicts between the user VLANs and the internal       VLANs. Issue the command show vlan internal usage on       a switch in order to display the internally assigned VLANs.

Switch#show vlan internal usage

VLAN Usage
---- --------------------
1006 online diag vlan0
1007 online diag vlan1
1008 online diag vlan2
1009 online diag vlan3
1010 online diag vlan4
1011 online diag vlan5
1012 PM vlan process (trunk tagging)
1013 Port-channel100
1014 Control Plane Protection
1015 L3 multicast partial shortcuts for VPN 0
1016 vrf_0_vlan0
1017 Egress internal vlan
1018 Multicast VPN 0 QOS vlan
1019 IPv6 Multicast Egress multicast
1020 GigabitEthernet5/1
1021 ATM7/0/0
1022 ATM7/0/0.1
1023 FastEthernet3/1
1024 FastEthernet3/2

In Native IOS, vlan internal allocation policy       descending can be configured so the internal VLANs are allocated       in descending order.



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