How to control any Loop in switch

Unanswered Question
Mar 13th, 2008


We have two cisco 4500 series switches in connected in HSRP mode with multiple trunk ports. The STP is PVST.

Currently the ISP has provided a single internet link from their switch -1 its now connected to our 4500 switch-1.

For redunt purpose in ISP end, the ISP has added switch-2 and given the Link-2 for us.

if i connect to Link-2 in 4500 switch-2 in my end it may form a loop. How to avoid any loop as the ISP end configurations is not in my control.



I have this problem too.
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shivlu jain Sat, 03/15/2008 - 02:11

you can use mstp and use the both links or simply run mstp.



Edison Ortiz Sat, 03/15/2008 - 09:19

How the ISP is handing down this connection?

Do they provide an IP address for your end device or is strictly Layer2?

If they provide an IP address, you can eliminate any looping or blocking ports by treating the 4500 as a true router.

You can run the switchport on both 4500s in routed mode instead of switchport/layer2 mode.

Routed Mode:

interface fx/x

no switchport

ip address x.x.x.x y.y.y.y

Layer2 Mode:

interface fx/x


switchport mode access

switchport access vlan x

interface vlan x

ip address x.x.x.x y.y.y.y





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