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Cisco 3750 Vlan Setup

Posted on 2013-01-19
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Last Modified: 2013-01-19
I have inherited a site with 3 x 3750's joined together in a single stack.

The current vlan setup is below and just woundered why you would use standby IP's on some vlans and secondary IP's on others when the switches are a single stack.

Thank you in advance.

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interface Vlan1
 ip address 10.42.0.9 255.255.0.0 secondary
 ip address 10.42.0.8 255.255.0.0
 ip broadcast-address 10.42.255.255
 standby 0 ip 10.42.202.1
!
interface Vlan21
 ip address 10.255.248.80 255.255.255.0 secondary
 ip address 10.255.248.1 255.255.255.0
 ip broadcast-address 10.255.248.255
!
interface Vlan41
 ip address 10.10.0.70 255.255.248.0
 ip helper-address 10.42.7.100
 ip helper-address 10.42.7.110
 ip helper-address 10.42.7.120
 standby 0 preempt
 standby 41 ip 10.10.0.1
 standby 41 priority 200
 standby 41 preempt
!
interface Vlan42
 ip address 10.10.16.80 255.255.248.0
 ip broadcast-address 10.10.23.255
 ip helper-address 10.42.7.100
 ip helper-address 10.42.7.110
 ip helper-address 10.42.7.120
 standby 42 ip 10.10.16.1
 standby 42 priority 200
 standby 42 preempt
!
interface Vlan43
 ip address 10.10.24.80 255.255.248.0
 ip broadcast-address 10.10.31.255
 ip helper-address 10.42.7.100
 ip helper-address 10.42.7.110
 ip helper-address 10.42.7.120
 standby 43 ip 10.10.24.1
 standby 43 priority 200
 standby 43 preempt
!
interface Vlan44
 ip address 10.10.48.250 255.255.248.0
 ip broadcast-address 10.10.55.255
 standby 44 ip 10.10.48.1
!
interface Vlan45
 no ip address
!
interface Vlan46
 ip address 10.10.56.1 255.255.248.0 secondary
 ip address 10.10.56.80 255.255.248.0
 ip broadcast-address 10.10.63.255
!
interface Vlan47
 ip address 10.10.64.1 255.255.248.0 secondary
 ip address 10.10.64.80 255.255.248.0
 ip broadcast-address 10.10.71.255
!
interface Vlan48
 ip address 10.10.72.1 255.255.248.0 secondary
 ip address 10.10.72.80 255.255.248.0
 ip broadcast-address 10.10.79.255
!
interface Vlan49
 ip address 10.10.80.1 255.255.248.0 secondary
 ip address 10.10.80.80 255.255.248.0
 ip broadcast-address 10.10.87.255
0
Comment
Question by:Mongo Peck
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6 Comments
 
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Expert Comment

by:Don Johnston
Comment Utility
Ah the fun of taking over a new network with limited documentation. :-)

"standby ip" defines the virtual address in HSRP. There's probably another router or switch. Do a "show standby brief" to verify.

The "secondary" ip addresses could be there for a migration from one addressing scheme to another.

Then again, they could be remnants of some previous function and are no longer relevant. If you don't see any HSRP neighbors, then you could probably remove the standby statements.

Check the arp cache over a period of days. If you don't see any entries for the some of the address ranges, then you could remove those ip addresses.

Just be ready to put things back once the phone rings. :-o
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Author Comment

by:Mongo Peck
Comment Utility
Thank you..

I believe the intial setup was 2 x 3560's running HSRP therefore the standby would be relevent.

Would I be correct to assume that as the 3750's are a single 3 switch stack then HSRP is not needed as if one switch fails the VLAN Information / IP's is still contactable with the other switches in the stack ?

Or do I need to read a little more ;-)
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Expert Comment

by:Don Johnston
Comment Utility
Do a show Standby brief. If there are no peers, then you can probably remove that.
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Author Comment

by:Mongo Peck
Comment Utility
Heres the output.

And thank you


Interface   Grp  Pri P State   Active          Standby         Virtual IP
Vl1         0    100   Active  local           unknown         10.42.202.1
Vl41        41   200 P Active  local           unknown         10.10.0.1
Vl42        42   200 P Active  local           unknown         10.10.16.1
Vl43        43   200 P Active  local           unknown         10.10.24.1
Vl44        44   100   Active  local           unknown         10.10.48.1
Vl82        0    250 P Active  local           unknown         10.255.253.254
Vl997       0    200 P Active  local           unknown         10.255.254.1
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Don Johnston earned 500 total points
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Yep... no peers. You can probably delete the HSRP configs.
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Author Closing Comment

by:Mongo Peck
Comment Utility
Great Expert
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