Radia Perlman Talk on TRILL and Spanning Tree

I found this YouTube Google Tech Talks presentation by Radia Perlman. She is often referred to as the "Mother of the Internet". She invented the spanning tree algorithm. She also invented concepts that made "link state routing" stable, scalable, and easy to manage. The protocol was adopted and renamed IS-IS. She is credited as creating the original concept of TRILL.

Her presentation is titled "Routing Without Tears; Bridging Without Danger". She discusses the creation of spanning tree, link state routing protocols and finally TRILL or Transparent Interconnection of Lots of Links. Those of of working with network infrastructure and Cloud Computing can really appreciate everything she has done.

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The Best Solution is the Simplest Solution

As a consultant I am sometimes brought into, shall we say, challenging situations. Some situations are primarily politically challenging, others are technologically challenging.

Today I have met a technically challenging situation. I am working on a network that is not, on the surface, much different than many others. In this case, the problem is someone has, from the technology or geek standpoint, created a very complex network. We have OSPF, EIGRP, and static routes. OSPF and EIGRP redistributing each other, and each redistributing static routes, plus back door links.

Now this environment had some challenging networking issues to deal with. However I am thinking of my favorite philosophical law called  Ockham's Razor. "It is a principle urging one to select among competing hypotheses that which makes the fewest assumptions and thereby offers the simplest explanation of the effect."

Sometimes the best solution is the simplest.

Cisco Configuration Tip - 3rd Party SFP Modules

It is possible to use non-Cisco SPF modules in a Cisco Catalyst switch. By default this is forbidden not allowed, but a top secret hidden command can make this happen.

switch(config)#service unsupported-transceiver
switch(config)#no errdisable detect cause gbic-invalid

In the SFP modules EEPROM, a Serial Number, Vendor Name & ID, Security code and a CRC. The switch reads these values and if they are not "Cisco" values reports an error such as:


%PHY-4-UNSUPPORTED_TRANSCEIVER: Unsupported transceiver found in Gi1/0/1
%GBIC_SECURITY_CRYPT-4-VN_DATA_CRC_ERROR: GBIC in port 65538 has bad crc


The official position from Cisco is:

Q. Do the Cisco Catalyst 3750 Series Switches interoperate with SFPs from other vendors?
A. Yes, starting from 12.2(25)SE release, the user has the option via CLI to turn on the support for 3rd party SFPs. However, the Cisco TAC will not support such 3rd party SFPs. In the event of any link error involving such 3rd party SFPs the customer will have to replace 3rd party SFPs with Cisco SFPs before any troubleshooting can be done by TAC.

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Cisco Press eBook Deal of the Day


Billy Carter

Cisco Configuration Tip - Command Macro To Change IP Address

Remotely changing an IP address on a Cisco router or switch, or moving an IP from one interface to another can be a challenge.

Cisco allows you to use macros although I have not really worked with them. rekrowteN has a great blog post about using macros to move an IP address from one VLAN interface to another.

In a previous Configuration Tip I discussed using the reload in/at commands to prevent getting locked out of a router or switch.

In this scenario we need to move the IP Address assigned to interface VLAN 1 to VLAN 10.

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For this tip start by entering reload in 15.


Next we create the macro

conf t
macro name mgmtchange
interface vlan 1
no ip address
shutdown
interface vlan 10
ip address 172.16.1.1 255.255.255.0
no shutdown
@

The "@" signifys  at the end of the macro. To apply the macro enter:

conf t
macro global apply mgmtchange

Once the change is made and you can reconnect don't forget reload cancel.

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Configuring Command Macros


Have you used macro's? What Macro scripts do you use?

Cisco Configuration Tip - Protect Your Tail

I have long been a fan of the Cisco "reload in/at" commands. These have saved my tail a number of times. This enables a brave network engineer to schedule a device reload for either a specific amount of time from now, 15 minutes, or just a specific time such as 11:00pm.

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Protect Your Tail

This has saved my tail a few times when working on a remote device. When changing ACLs or firewall rules there is always the potential of getting locked out. It has also saved me when debug messages flooded a device and I could not get the telnet/ssh session to respond.

Bonus Tip: When I have to debug a router or a switch I open a second telnet/ssh window. The primary window is set to terminal monitor so I can see the messages. In the second window I type in "undebug all" but don't press enter. If the debug messages get out of hand in the primary window, I switch to the second window and hit enter.

 Before making configuration changes, do the following:

copy run start
terminal monitor (so you can see reload countdown warnings
reload in 15

You are now free to make changes. If you get locked out, sit back and wait for the reload.

When you have made changes and still have access type:

reload cancel
copy run start

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