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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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how to upgrade stacked S5300 switches

When a single switch is upgraded, services are interrupted about 3 minutes. This time increases when a stack is upgraded. Methods of upgrading the system software of S5300 and S6300 are the same. We can focus on Huawei S5300 switch as an example. Let’s assume we have 2 switches in the stack.

<labnario> display stack
Stack topology type: Ring
Stack system MAC: 80fb-06b1-69eb
MAC switch delay time: 10 min
Stack reserved vlanid : 100
Slot#     role        Mac address      Priority   Device type
------    ----        --------------   ------     -------
    0     Master      80fb-06b1-69eb   100        S5352C-EI
    1     Standby     80fb-06ab-f6e3   120        S5352C-EI

At first you have to check a space of flash memory of the switch. If there is no enough space in the flash to fit a new system software, just delete the old (current) system software, for both Master and Member switches:

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how to find TC packets source on Huawei switch

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.

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how to configure trunk between Huawei router and switch

What we want to do is to configure 802.1q trunk between labnario1 router and labnarioSW1 switch, so that hosts from VLAN 100 will be able to ping the router’s interface.

Let’s look at the simple topology:

First we want to configure labnario1 router. To configure Ge0/0/1 interface to operate as a 802.1q trunk, we need to configure it as follows:

[labnario1]interface GigabitEthernet 0/0/1
[labnario1-GigabitEthernet0/0/1]port link-type trunk

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how to display power of optical module

Let’s take Huawei’s S3328TP-SI switch as an example. This switch has 2 combo ports, which can be changed either to optical or electrical mode.

[Quidway]display elabel
[Board Properties]
Description=Quidway S3328TP-SI,CX5Z228AM,S3328TP-SI Mainframe(24 10/100 BASE-T ports and 2 Combo GE(10/100/1000 BASE-T+100/1000 Base-X) ports and 2 SFP GE (1000 BASE-X) ports (SFP Req.) and AC 110/220V)

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