Alcatel Unleashed

devnull wrote:Loopback deteciton (as far as i understand) should prevent Loops, that are not blocked by stp, eg on ports where stp is filtered or Devices (like my siemens phone), that somehow drops stp and thus creates a L2 loop.

From release Notes:

Code: Select all

LBD can detect and prevent L2 forwarding loops on port either in the absence of other loop-detection 
mechanisms like STP/RSTP/MSTP or when the mechanism can‟t detected it. Sometimes the 
STP/RSTP/MSTP based loop detection can‟t be used due to the following Facts 
- There is a client‟s equipment that drops or cuts the BPDUs.
- The STP protocol is restricted on edge Network
The LBD feature detects that a port has been looped back or looped. If a loop-back/loop is detected, 
the port is disabled (forced down) and the appropriate Error Log is issued.

So do you have a loop in your network, when you

a) I make a first loopback on the other swith (connected on the stack on the port 1/10 for example) : nothing
b) I break the loopback and make it again : loopback is detected, the port 1/10 is shutdown for 30 secondes : it works

In case a): do you have a l2 loop, e.g. network interface goes to 100% transmit, cpu high ...

Yes, I had only this when I do the first loopback.

devnull wrote: or is this case just blocked by e.g. stp ?

If you have a loop (with resulting impacts on your network) i would open a SR (and please keep me updated). If this is just a "it's blocked somehow else" i would not care too much.

I just want the switch shutdown automatically the port where loopback is detected. So, it works on the second loopback, not on the first...

then i would open a SR and provide them with the necessary data.

devnull wrote:then i would open a SR and provide them with the necessary data.

Thanks

Hello,

I update this post because now its working. I erase all my config and do and new conf step by step. I think I had a problem with the old config.

Thank you all for your support.

Hello
I need advice how to prevent loop in MC-lAG OS10k Environment ? From time to time someone connect dumb L2 switch to network and make loop on that dumb l2 switch. Tried everything, qos policies, loop-detection, bpdu guards and everything what i found here doesn't work. It is realyy disaster becouse when the loop occured MC-LAG bring down ALL aggregation and i need restart one core to restore connectivity (really no command like "no multi-chassis loop-detection 2/1" for example, why need i restart core to delete interface from disable mode ?) try to find a loop, remove the loop and restart second core to return MC-LAG synchronisation.

How did it kill all your network? The times i had a loop detected it was only one of the MC-LAGS shut down (if i create a link between e.g. MC-LAG LACP 96 to 97 switches) or a single lag (when someone somehow created a loop behind a single MC-LAG-LACP)

You can always use
clear multi-chassis loopback-detection, to clear a detected loop info, shutdown and reenable the ports, that got blocked
(int 1/17 adm sta dis, int 1/17 adm sta ena)
Afterwards it should "only" reblock the affected links if you did not fix the loop.

But i must admit i faced a similar problem with some real strange loop occurence, which i was not blocked by loopback detection - i had to use divide an conquer on a attached switch to identifiy the port in question. E.g. block 50% of ports, see if loop resurfaces - if yes unblock that 50% (you know it must be on the other half) and block half of the remaining ports..

If everything fails you can disable loopback detection on MC-LAG, but than you must life with the loop - which may be the better solution depending on the network..

Ok too much emotions was in me Loop dont kill all my network, only this aggregation when loop occured, but if it is stack when i have connect servers then i have a problems Thx for tip how to reenable port after loop detected. I used this commanf before but dont think about disable/enable port after that. Some time ago i disable loop detection on 10k but it was problematic with mac address leraning. IN my case computetrs with WIndows Vista and Windows 7 cant find default gateway (VIP address) i had to make static arp with mac address and ip of default gateway. Strange was that on linux amchines and Windows XP there was no problem.

Yeah i know that - in my case it killed a MLAG to a whole building, which was also not nice.
Never had your problem with mac-learning, has it been fixed in newer releases?

If you can test try with loopback-detection on edge switch (reduce transmit interval, use current code) - maybe you need to slow down loopbackdetection interval on the 6900?
e.g. 5 sec transmit-interval on edge, 10 secs on MC-LAG?

otherwise: if you can reproduce a loop that is not catched by loopback-detection: open a ticket to get that fixed..