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4800G + L2 loop prevention / protection on 1 port?

Kimera
Occasional Contributor

4800G + L2 loop prevention / protection on 1 port?

Hi,



does the 4800G have something like loop prevention / loop protection builtin?



Just in case someone brings down the network if he builts a loop e.g.

At the moment with our old equipment if this happens the hole segment andnearly the hole network goes down, e.g. 4800G ----port 22---- small mini 4 port switch ---- somethat builts a loop on the mini switch





So would it be possible to protect me? Everybody says, use STP, but I do not have any doubled switches, no redundancy. Can STP used in such a situation?





3 REPLIES
roo5ter
Occasional Advisor

Re: 4800G + L2 loop prevention / protection on 1 port?

STP / RSTP should do the trick. I'm using a 5500G-EI as the core with no redundancy (connected to a bunch of smaller managed and unmanaged switches) and have the following commands in place. Keep in mind the 4800G may have a different syntax.



stp mode rstp

stp instance 0 root primary



And any physical interfaces that are "edge" should to have the following command in place:



stp edged-port enable



Personally I set ALL ports to "edged" as the switch should automatically turn on and off fastport if it determines the port is an edge device. This will speed up DHCP responses.



In this scenario if a cheap unmanaged switch plugged into the core's port 3 gets looped, STP will set port 3 to discarding packets. You can view the current state of ports with a "dis stp" command.

Jirkaehm
Advisor

Re: 4800G + L2 loop prevention / protection on 1 port?

I would also recommend to use loopback-detection function.



Problem is that STP is unable to find loop, if you have it on unmanagaded switch.

I have seen many network's completly down because of one unmanaged switch in presentation room which had connected both end's of the cable to it :)



loopback-detection need to be turned in system-view and then on every edge port loopback-detection enable.

roo5ter
Occasional Advisor

Re: 4800G + L2 loop prevention / protection on 1 port?

Thank you Jirkaehm. I forgot to put a "stp loop" command under the physical interface config in my message due to lack of sleep.



Also make sure "stp enable" is set, which it should be already.

This message was edited by roo5ter on 4-27-09 @ 12:52 PM