Always Networks Blog - Cisco

Design Consideration - The effects of VLAN ID's on Spanning-Tree convergence

Network Switch

When designing a network, consideration should be given to separating traffic into VLANs. This is done for logical separation, security and performance reasons.

This affects the convergence of a Layer 2 Network. Most Cisco switches running STP (Spanning-Tree Protocol) will be running an instance per VLAN. This is called PVST (Per VLAN Spanning-Tree), or RPVST (Rapid Per VLAN Spanning-Tree), depending on whether you are running …

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Python Scripting on a Cisco Nexus 7k

A few days ago I stumbled upon the python interpreter on the Nexus platform. It got me to tinkering.

In the past, I have had a requirement to grab a list of all of the interfaces on a box, the IP's, and the masks. The interfaces and IP's can easily be obtained from a show ip int br, and using column select to grab the …

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Nexus 7000 Software Bug - Flash RAID Errors - Part 2

Wed 12 August 2015

This is a continuation of a previous post.

The last post finished where we thought all was good, because the flash status code was reading 0xF0, which we were told means both flash drives are healthy. What we noticed though was that the diag tests were still failing for compact flash - test 7 - on some of the sups. Initially Cisco told us that this was …

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Nexus 7000 Software Bug - Flash RAID Errors - 7k Reboot and Failover

It's been a mad couple of weeks with Nexus 7000's. My client hit a software bug on their Nexus 7k, which turned out to be a most impressive bug. It basically causes the flash drives to be erroneously marked as faulty, which then causes them to be remounted in read only. The first symptom was that you could not save the running configuration by running …

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Replacing a failed Cisco Ironport Web Security Appliance Proxy

Recently we had a Cisco Web Security Appliance (WSA) Proxy fail. When I say fail, I mean a single stick of RAM failed after a reboot. Cisco said RAM isn't replaceable so we had to RMA the whole box (odd for a device that is basically a rebadged server...maybe I have a money saving idea for you Cisco!)

There were a few steps to …

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Cisco Nexus 1000v Module in "Other" state

What you don't need while you are checking your morning emails and drinking your first cup of coffee of the day is to receive an email saying that the VSM for the Nexus 1k has rebooted.

By the time we logged on to the Nexus 1000v, it was back up. "show system redundancy status" showed both VSM's (supervisors) as being up and HA. The "show …

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CCIE Written Blueprint: 1.3.c Interpret packet capture

Thu 09 October 2014

This is a very short section! I didn't see the point in harping on about wireshark, I use it most days at work. And the IOS embedded packet capture was discussed in length further up the blueprint (i.e. in a previous blog post).

1.3.c Interpret packet capture

1.3.c (i) Using Wireshark trace analyzer

Packet capture can be obtained using a …

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CCIE Written Blueprint: 1.3.b Apply troubleshooting methodologies

Sat 04 October 2014

This is another difficult section in the blueprint to write about. I find troubleshooting techniques and methodologies to be quite personal; no two people's brains work the same way. I guess this is based on how I do things and some tips I've received from a few people over the years.

1.3.b (i) Diagnose the root cause of networking issue (analyze symptoms, identify …

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CCIE Written Blueprint: 1.3.a Use IOS troubleshooting tools

1.3.a Use IOS troubleshooting tools

1.3.a (i) debug, conditional debug

Debugs can be used on a wide range of functions (debug ?). Some debugs can be very noisy. Debug conditions can be set to filter out some of the noise – for example debug condition interface fa0/0 will limit the debug information to things using that interface. Undebug all does not remove …

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CCIE Written Blueprint: 1.2.a Evaluate proposed changes to a network

Tue 09 September 2014

As the blueprint goes, this is, in my opinion, the most vague topic to write about. It is dependent on the understanding of the topics, and how the changes will impact the existing network. I have skimmed through this really, with the intention of covering the topics in their actual topic sections. I am pretty used to evaluating impact - I seem to spend my entire …

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