Month: October 2013

GNS3 topology for INE Workbook

Now that my topology in GNS3 is exactly as in INE Workbook 1 I can share it with you if you don’t want to do all the basic configurations and connections by yourself.

After spending too much money on different rack rentals in the past few months I decided that I will definitely need to try to use GNS3 for simulating my CCIE labs. It will be the only solution if I didn’t want to spend all my money and then have no more left to pay myself trip to Cisco HQ.

GNS3 BGP topology

After one whole day of struggling with different GNS3 issues I did succeed to configure almost everything. From now I am able to use GNS3 for almost all chapters of my loved INE Workbook VOL.1 and probably VOL.2 also.

There are some things that are not available on GNS3 simulated IOS and I will try to list them below at some point. Other thing that took me some time are that the interfaces are named differently. Cisco Etherswitch Module is added to router in GNS3 order to simulate some basic switch features that is normally not available in GNS3. There is no way to use 0/0 – 0/21 port names on that Etherswitch Module. The interfaces are 1/0 – 1/15 so you cannot do nobrainer paste of config to those “switch” devices. Some serial interfaces are for example Serial 0/0 and in the workbook they are Serial 0/0/0 so this is another one. There are furthermore some other changes to witch interfaces are different devices connected but all the devices now are connected to all other devices exactly as in VOL.1 physical topology. This file down there is prepared for BGP lab chapter of INE Workbook 1. but keep in mind that it can be good for all other parts of the Workbook as the interface configuration is not changed across the Workbook 1 so you just need to modify routing to get started with other chapters.

Do the topology by yourself, you will learn more!

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Forwarding UDP broadcast traffic mechanisms

We will speak here about some basics about Forwarding UDP broadcast traffic. If you were wondering what Forwarding UDP broadcast traffic actually is I will try to explain it here in few words.

If you have more that one broadcast domains in your local network, let’s say that you have three VLANs. In normal networking theory it’s normal that broadcast initiated on host inside one VLAN will get to all host inside that VLAN but it will not get across to other VLAN. Typically the broadcast domain border is router or a Layer’s 3 switch VLAN interface. Although this is normal for most of broadcast traffic there needs to be a way to forward some kinds of broadcast traffic across that border. Why? Here’s a simple example. If you use DHCP, and you are, you will probably have hosts in different VLANs and all of them need to get the IP address from DHCP. If Forwarding UDP broadcast traffic didn’t exist it will be needed to have one DHCP server on every VLAN. Remember that DHCP works using broadcast traffic in some of the steps.

Simple DHCP address leasing:

Host that connects on the network will in the first step send broadcast DHCP discover message in order to find where the server is or if the server actually exist. After the HDCP replies with unicast DHCP offer host will one again use broadcast to send DHCP request to server. Server will then acknowledge the IP address leasing with unicast ACK message and that’s it.

 DHCP steps

Forwarding UDP broadcast traffic

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