Saturday , June 3 2023

BFD process-interface-status vs. process-pst

BFD process-interface-status and process-pst are applicable only for single-hop BFD. Let’s assume that we have two routers directly connected through interface GE1/0/0.


By associating BFD session status with interface status we can trigger fast route convergence. We can use this function only for BFD session that uses a default multicast IP address to detect the single-hop link. We can use association between BFD session status and interface status in the case, when transport devices exist on the link between the routers. As the actual physical path is segmented by transport devices, the routers on both ends need a long time to detect a fault that occurred on the link. The change of BFD status affects the protocol status of the interface and thus fast convergence is triggered. When the BFD session becomes DOWN, the correspondence interface status also goes to BFD_DOWN state, causing that this direct route is deleted from the routing table but the router can still forward BFD packets.

[Labnario] bfd
[Labnario-bfd] quit
[Labnario] bfd test bind peer-ip default-ip interface gigabitethernet 1/0/0
[Labnario-bfd-session-test] discriminator local 1
[Labnario-bfd-session-test] discriminator remote 2
[Labnario-bfd-session-test] process-interface-status
[Labnario-bfd-session-test] commit

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Huawei cheat sheet – Huawei CLI

I have been describing Huawei datacom devices on my blog since July 2011. I started with some basic information about Huawei CLI, access methods and upgrade procedures. Then I showed you more advanced topics like PBR, DHCP etc. I am pleasantly surprised that this blog is visited by people from all continents, even from countries I have never heard about. As this blog is getting more and more popular I will do my best to publish more interesting posts.

As we went through a some stage, I have decided to prepare a cheat sheet describing Huawei CLI. You can download it as PDF, print and keep it :). I hope it will be useful for you.

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console password recovery Huawei S5300

What to do if you forgot console password to Huawei S5300 switch?

I received such question last week. One of readers of this blog forgot console password and he wanted to modify startup configuration file from bootrom menu. His operation failed and there was a notification from the system that there is an “invalid package file!” and “auto-booting failed!”.

There was s5300ei-v100r002c02spc100 software installed in this switch so we can focus just on this software.

In S5300 there are two ways to solve this problem:

  1. Create configuration file on your PC, upload it to S5300 and modify startup file
  2. Delete configuration file from S5300 to let it to boot with empty configuration

Let’s start with the first way:

  • Create configuration file on your PC. You can use default empty configuration downloaded from another switch
  • Start FTP server on your PC
  • Upload the configuration file to flash of S5300 from bootrom menu:

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a few words about BFD

BFD (Bidirectional Forwarding Detection)

What to do to quickly establish an alternative path in case of communication failure between adjacent systems?

There are two detection mechanisms:

  • Hardware detection, for example alarms in SDH used to detect link faults
  • Hello mechanism used by routing protocols.

The main disadvantage of hardware detection is that not all media support it. For example Ethernet does not provide this kind of signalling.

When there is no hardware signalling we can use Hello in routing protocols but this mechanism is relatively slow. Sensitive services, for example voice, cannot work with more than one second delay.

The best solution is to use BFD (Bidirectional Forwarding Detection). This is simple mechanism that works independently of media, data and routing protocols. The main goal of BFD is to detect failures in the path between adjacent devices in a short time (minimum detection time for NE40E is 30ms). It does not matter if it is physical link, virtual circuit, tunnel, MPLS LSP, multi-hop path or unidirectional link. We can treat BFD as a simple Hello protocol where a pair of devices periodically sends BFD packets between them. If one device does not receive BFD packets within specified period, the system assumes that the bidirectional path to the neighboring system has failed.

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Huawei interface backup configuration

There are two interface backup modes:

  1. Active/standby
  2. Load balancing

In common active/standby mode only one interface transmit services at any time. When active interface works properly, it transmit all the traffic. In case of fault of the primary interface, a backup interface with the highest priority starts transmitting packets. If primary interface recovers, traffic is switched back to active interface.

In load balancing mode, in case traffic volume exceeds an upper threshold set for active interface, a backup interface with the highest priority starts transmitting packets and load balancing is performed.

Which mode we have is determined by upper and lower thresholds. If thresholds are not set, active/standby mode is used. Otherwise, load balancing mode is used.

Let’s assume that we have the following topology:

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