Thursday , September 19 2019

Huawei eNSP – news

A new version of Huawei simulator eNSP has been released. One of new features is AR CPU reduction. Besides that, reboot functionality of AR router has been provided. Also a few features have been modified. All information you can find in a release notes for this version.

Download, test and enjoy!

huawei-enterprise-network-simulation-platform

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how to find “TTL exceeded” packets

Let’s imagine you are an IP engineer and suddenly found increasing number of “TTL exceeded” packets on your router. Your first thought is “what the hell is it? How to find a source of these packets?”

Take it easy. You will know how to investigate such issue on Huawei router.

[labnario]display ip statistics
  Input:     sum               2783201      local               2321967
             bad protocol            0      bad format                0
             bad checksum            0      bad options               0
             discard srr             0      TTL exceeded         494196
  Output:    forwarding              0      local                886008
             dropped                 0      no route                  0
  Fragment:  input                   0      output                    0
             dropped                 0
             fragmented              0      couldn't fragment         0
  Reassembling:sum                   0      timeouts                  0

As you can see there are “TTL exceeded” packets. “Display ip statistics” command shows packets that are directed to CPU. Don’t mix it up with packets found on the interface. For example, you don’t have dropped packets on the interface but “display ip statistics” shows such packets.

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Link Flapping Protection on Huawei switches

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.

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BGP LocPref once again

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.

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BGP default local preference in Huawei CLI

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.

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