FirstDigest » Cisco-routing

RIPv2 MD5 authentication – routing trick

Calin — Fri, 30 Sep 2011 13:45:58 +0000

I must admit that the following example is more a CCIE exam topic and not a solution that you would add in real network environments.

Let’s assume that we have the following topology:

The Loopback interfaces are there to have some networks which we will advertise into RIPv2. The request for this topic is to have RIPv2 MD5 authentication in place, Router1 to receive all routes from Router2, but Router2 will not have any prefixes in routing table from [...]

InterVLAN routing using Private VLANs

Calin — Fri, 23 Sep 2011 13:04:06 +0000

Private VLANs is one possible solutions for service providers to offer secure connections to their customers and avoid inter-vlan communication in the same switched environment.

I’m sure that you heard (and most probably practice already) InterVLAN routing. When it comes to Private VLANs the routing part may be a bit tricky. Keep in mind that this is not something that I would recommend to use as a standard in a productive environment, but for things like Cisco exams (e.g. CCIE R&S) or last resort solution, [...]

Cisco Easy VPN Router-to-Router

Calin — Fri, 16 Sep 2011 09:17:12 +0000

Cisco Easy VPN is not a new technology. Actually it is pretty old, but still used by many companies or people to connect remote site / remote workers to headquarter.

A few days ago I was looking to connect a remote site in a simple way but still secure and a colleagues suggested me to use Easy VPN. It supposed to be a simple configuration and it was after solving all issues that came into play.

First of all, I needed an Easy VPN Router(client) [...]

Interface software loop

Calin — Tue, 30 Aug 2011 08:13:13 +0000

If you ever worked in an environment where you have to deal with leased / dedicated lines provider by your SP (service provider) then you know that whenever it’s a problem on the line they request, if possible, to put a loop on the line from one end toward the other end, so they can do some measurements. Usually from my experience with SP, this is a standard approach in case that they don’t know exactly what problem is with your line or where the [...]

Cisco: Port-channel load-balancing explanation [Part I]

Calin — Mon, 30 Aug 2010 14:26:31 +0000

Port-channel (or etherchannel) is a great way to increase the transport capacity between 2 switches or between a switch and an end device that suport load balancing (e.g. server). Today I don’t want to focus on how the Port-channel are configured, but more on how they load-balance the traffic over the multiple interfaces included in a bundle.

To configure the port-channel load balance, you have to be in the config mode and issue:

port-channel load-balance method

port-channel load-balance method module slot

the method [...]

Cisco: Policy Routing with IP SLA

Calin — Thu, 27 May 2010 12:06:03 +0000

Let’s assume that you have a Cisco router with 2 ISP connection. The first one it’s a 10Mbps connection with a decent latency and the second one it’s a 2Mbps connection with quite high latency.

Since you don’t want to load balance over this 2 connections for the obvious reasons described above, you decide to to use the 10Mbps connection as the primary link and the 2Mbps one as a backup, just in case that the primary link fails.

You have no dynamic routing protocol, just a [...]

Cisco: How to configure HSRP

Calin — Fri, 25 Sep 2009 13:59:45 +0000

In this post I proposed to discuss a little bit about Hot Standby Router Protocol and how it can be configured on a Cisco device. For this I have chosen the following topology:

I had in mind this scenario due to the fact that the traffic can take multiple paths in case of link being down and this give us the possibility to have a little bit of conversation on HSRP topic.
HSRP is defined in the document [...]

Cisco: OSPF conditional inject of a Default Route

Calin — Tue, 16 Jun 2009 12:59:01 +0000

I believe most of you are familiar how OSPF is injecting a default route in a normal area. If not, you can find here all the documentation that you need. Please be familiar with this concept before reading this article.

Now, let’s assume that we have the following topology (click on image to have a more detailed view) :

As you can see we [...]

Cisco: How to selective drop packets without using an access-list

Calin — Thu, 05 Mar 2009 13:17:37 +0000

The title actually was a request that I encounter during my CCIE RS preparation. Of course, that in the real world, I would go straight forward and implement an access-list do drop selected packets. But since the lab environment is different for the real one, you might get a task like the above one.

Let’s assume that we have a network topology with a central router (R1) that connects 2 routers (R2 and R3), like in a hub and spoke diagram. Communication between R2 and [...]

Cisco: Engineer’s trick to avoid suboptimal path

Calin — Fri, 16 Jan 2009 09:09:24 +0000

I was explaining in the previous post what is the difference between optimal and suboptimal path and how to avoid the use of not such a good path in your routed environment. Also there I presented this so call “dirty trick” you can use to force the routing protocol to choose the path that you want, based on the Administrative distance modification.

As I said there is another way (for sure more than one) to do it, using [...]