05-07-2007 11:36 PM - edited 03-05-2019 03:55 PM
Hi,
Were running a network of 2550 switches and have come across the following configs for customer and trunk connections. These configs haven?t been uniformly rolled out across the network and we?ve also been experiencing issues whereby were having to clear tables and reset interfaces to bring back certain rings in the network.
interface FastEthernet0/1
description ** TRUNK TO NETWORK SWITCH **
switchport trunk allowed vlan 10,50,56,58,80,90,91,96,100-102,150,200,208,216
switchport trunk allowed vlan add 218,802,805,806,809
switchport trunk pruning vlan none
switchport mode trunk
storm-control broadcast level 0.30
storm-control action trap
spanning-tree cost 110
interface FastEthernet0/2
description **CUSTOMER CONNECTION**
switchport access vlan 10
switchport trunk native vlan 10
switchport trunk allowed vlan 10,56,806
switchport trunk pruning vlan none
switchport mode trunk
storm-control broadcast level 0.10
storm-control action trap
no cdp enable
interface Vlan1 shutdown
!
interface Vlan10 ip address x.x.x.x x.x.x.x
Questions are:
a) The trunk interface config ? the ?allowed VLAN? cmd is self explanatory but what are the real benefits? Obvioulsy this command isn?t scalable with a large number of VLANs and Id like to drop this config.
b) Does the ?allowed VLAN? cmd effect STP .. ie if a VLAN is allowed on a fwding trunk port but not configured on a blocked port , if the blocked port switches to fwding is this VLAN still allowed to traverse this trunk?
c) The customer connection port appears to make little sense. Its configured as an access port but has trunking cmds configured? Again, is there any benefit to this command?
d)
Im looking to tidy up the config to isolate the issues weve been experiencing. Any help would be much appreciated.
Many thanks.
Solved! Go to Solution.
05-08-2007 12:25 AM
Hi
Then yes, the connection needs to be configured as a trunk and i can't see why you need the switchport access vlan 10 part of the configuration.
Also, just for reference it is suggested as best practice that your native vlan should be a completely unused vlan that is non-routable. On our data centre switches we use vlan 2 for management which is obviously routable and then we use vlan 999 as the native vlan. No switchports are placed into this vlan and there is no layer 3 SVI for vlan 999.
Jon
05-07-2007 11:43 PM
Hi
a) By only allowing certain vlans on your trunks you are increasing you security within your switch environment. More importantly your are also restricting STP propogation as STP traffic is not sent down the trunk links for vlans that are not allowed.
b) See a.
c) It is a bit of a mess. What shows up when you run a "sh int trunk" command. Does the customer need a trunk link or are all the ports in vlan 10 only. Also who manages this switch. You may find that your management IP address is in a different vlan than vlan 10 and hence even tho all the customer ports are in vlan 10 only you still may need a trunk link.
HTH
Jon
05-08-2007 12:09 AM
Hi Jon,
The switch is managed by ourselves and VLAN 10 is required for our internal mgt. The connecting switch is the customers. Output below:
B2MP_2950_01# sh int fa0/12 trunk
Port Mode Encapsulation Status Native vlan
Fa0/12 on 802.1q trunking 10
Port Vlans allowed on trunk
Fa0/12 10,56,806
Port Vlans allowed and active in management domain
Fa0/12 10,56,806
Port Vlans in spanning tree forwarding state and not pruned
Fa0/12 10,56,806
Youre right .. its a mess! :)
05-08-2007 12:25 AM
Hi
Then yes, the connection needs to be configured as a trunk and i can't see why you need the switchport access vlan 10 part of the configuration.
Also, just for reference it is suggested as best practice that your native vlan should be a completely unused vlan that is non-routable. On our data centre switches we use vlan 2 for management which is obviously routable and then we use vlan 999 as the native vlan. No switchports are placed into this vlan and there is no layer 3 SVI for vlan 999.
Jon
05-08-2007 04:01 AM
Thanks Jon for such a thorough and informed explanation.
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