Tag Archives: Huawei CLI

I have come across link flapping protection feature recently. It is available on S5700 switches. It looks like it is a new feature on Huawei switches. I had not met it in older hardware versions. That’s why I decided to write a few words about it. Unfortunatelly, although this command is available in Huawei network simulator eNSP, it does not work properly. But maybe you will have possibility check it on your real devices.

Port flapping (port going UP and DOWN continually) can be caused by a faulty cable, link failure, active/standby switchover, port hardware failure, etc. Frequent status changes on an interface can lead to:

• STP topology recalculation and changes,
• ARP entries updates,
• dynamic routing instability and convergence problems.

All these issues can negatively affect switch performance and should be avoided.

Link Flapping Protection is a feature that can be implemented on an interface to solve problems caused by the flapping port or link. It checks the interface flapping frequency and link flapping detection interval. If the number of interface flapping times reaches the limit, in a specified period, the interface is shut down.

Let’s keep going and try to configure BGP local preference attribute using route-policy.

We can take full advantage of topology and configuration from the last post: “BGP default local preference in Huawei CLI“.

1. Assure full connectivity based on the attached topology (look at the previous article).
2. Configure Loopback 10 and Loopback 20 on router AR4.
3. Import all Loopback interfaces of router AR4 to BGP.

Let’s assume that we have a topology like in below picture:

1. AR1, AR2 and AR3 are in AS 100.
2. AR4 is in AS 200.
3. Loopback 100 of router AR1 and loopback 0 of router AR4 are advertised by BGP.

What we want to do is to configure default local preference attribute, which will determine the optimal route, for traffic that leaves AS 100. In our case, the whole traffic leaving AS 100 will go through AR3.

If a BGP device obtains multiple routes from different IBGP peers and these routes have different next hops to the same destination, the BGP device will select the route with the greatest Local_Pref value.

Today a few words about 2 simple but useful commands: lock and send.

LOCK – prevents unauthorized users from operating on the current terminal interface

SEND – enables the system to transfer messages between user interfaces

Let’s look how they work on Huawei S5700 switch.

LOCK

<labnario>lock
Enter Password:
Confirm Password:

 Info: The terminal is locked. 

Enter Password:

<labnario>

Topology Change (TC) packets are sent when MSTP-enabled interface in a network flaps. If a physical interface frequently alternates between Up and Down, the MSTP status of the device in the network becomes unsteady. As a result, a large number of TC messages are generated, ARP entries are frequently deleted and services are interrupted.

How to find the source of TC packets?

Let’s look at the log, generated on one of the switches in a network. Let’s take Huawei S9300 switch as an example:

Dec 19 2012 11:32:56+10:00 S9300 %%01MSTP/6/RECEIVE_MSTITC(l)[40922]:MSTP received BPDU with TC, MSTP process 0 instance 0, port name is GigabitEthernet6/0/0.

What can we find in this log?

The most important for us is the port number on which the switch received TC packet, in this case interface GE6/0/0. To troubleshoot this problem we have to go to the next switch, connected to interface GE6/0/0 and check logs of that switch. If the neighbouring switch receives TC packets as well, we have to do further troubleshooting. If we find in the logs that MSTP-enabled interface is flapping, we can consider that this interface is the source of the TC packet. If this interface is still flapping, just make it down, to avoid unsteady behaviour.