Cisco | IPNET - Part 12

Cisco: OSPFv3 point-to-point network configuration

In the previous post I explained some basic stuff about IPv6 and how to configure IPv6 addresses on Cisco’s interfaces. Following this subject, I want to explain now how you can configure unicast dynamic routing protocols for IPv6 networks. The same as IPv4, the v6 generation of IP addresses supports routing protocol like OSPF, RIP and EIGRP, just that their names has been adapted to the v6 generation meaning OSPFv3, RIPng and EIGRP for IPv6.

From the routing protocols above I chose for today OSPFv3, because it is quite easy to understand and, why not, it is one my preferred routing protocols. OSPFv2 and OSPFv3 share the same key concepts, so if you understand the version for IPv4 you will have no problems to understand the one for IPv6. However, you should understand the most significant differences as well:
— to enable OSPFv3, you will have to use interface subcommands compared with the “network” statement under “router ospf” process in OSPFv2
— if there are multiple IPv6 addresses configured on a OSPFv3 enabled interface, then OPSFv3 advertise all the related networks
— OSPFv3 router-id (RID) has to be set in order to enable the routing protocol; this can be set automatically like in the OSPFv2 or manually
— OSPFv3 uses IPv4 for RID; if no IPv4 address is present on the router to be used as RID, than the OSPFv3 process cannot choose it’s RID
— OSPFv3 does not provide natively authentication like OSPFv2 does; for OSPFv3, the IPv6 structure covers this with its internal support for AH and ESP.
That’s about enough for you to configure a basic OSPFv3 routing protocol. If you are interested in more details about OSPFv3, you can check OSPFv3 documentation by Jeff Doyle and Jennifer Carroll on NetworkWorld.com

I will use the same topology like in the previous post. You can check here the IPv6 configuration of the routers. Please click below to see the tutorial:

If for some reasons the tutorial above is not available for you, please check this text file which present in text mode everything needed to enable OSPFv3 point-to-point network configuration between 2 Cisco devices.

Cisco: IPv6 basics and configuration how-to

Today, I had to deal with IPv6 configuration for my CCIE preparation and I said to write a small tutorial about IPv6 for it’s basic stuff. First of all IPv6 is not more complicated that IPv4, it just look like it is. Second, and this is my personal opinion, I think that as long as IPv4 will be on the market and things like NAT can overcome the problem of IP addresses being exhausted, IPv6 will not be implemented on a large scale. Let’s be honest, I’m more OK in a discussion saying that I had a problem with the IP address 192.168.100.100 than to say 2001:128:1F:633:207:85FF:FE80:71B8 (IPv6).

But what we like and what we have to know as network engineer, that’s a different story. For this reason I said that some information about IPv6 and how to configure it and test a point-to-point connection on a Cisco device, would not hurt anyone.

Some essential points about IPv6 (if you want more there is a lot of information on Internet):
-use of 128 bits compared with 32bits )IPv4
-IPv4 are represented in hexadecimal rather than decimal
-use colon-separated field of 16bits rather than 8 bits decimal points separator
The IPv6 can be write down in different formats. Let’s take:
2001:0001:0000:0000:00A1:0CC0:01AB:397A
this can look like:
2001:1:0:0:A1:CC0:1AB:397A – leading zero in each 16bits group can be eliminated
2001:0001::00A1:0CC0:01AB:397A – two or more 16bits “0000” groups can be write like :: (double colons) one time in the IPv6 address
2001:1::A1:CC0:1AB:397A-the simplest form to write the IPv6 address
A small, but very important hint. Take care of the following common mistake when you are writing IPv6 in short format. Let’s say that we have 2001:0000:0000:0000:00A1:0000:0000:397A and you want to write it in short format with the rule that 2 or more “0000” groups can be write like :: , and you write 2001::A1::397A which is wrong, because after this nobody or no device will know where it was 2 groups of zero and where 3. Taking the wrong format, you want to write the long format back and you can write it as: 2001:0000:0000:00A1:0000:0000:0000:397A, and obvious you can see the mistake.
There are more types of IPv6 address which you can find in the table below:
IPv6 addresses type

There are 3 ways in which you can assign an IPv6 to a Cisco device:
-manual = just like in the IPv4
-stateful autoconfiguration = you use a DHCP server that will assign and IPv6 address to the interface
-stateless autoconfiguration = the interface ID in IPv6 is configured locally by the host to be globally unique using the EUI-64 procedure

In short terms the EUI-64 procedure is used to autoconfigure the last 64bits of the 128bits IPv6 address, which is the interface ID portion. EUI-64 method take the MAC address of the interface (48 bits) which is unique and derives the interface ID (64bits). You’ll ask probably how come 48bits become 64bits. EUI-64 insert in the middle of the MAC address a 16bits portion equal to FFFE and set the universal/local bit (7th bit) to indicate global scope. More clearly, let’s say that the interface has the MAC address 00:07:88:80:71:b9 and IPv6 apply the EUI-64 method this will become 0207:88FF:FE80:71b9 (last 64bits = interface ID).

After this short information (trust me it is short compared to detailed books) I hope that the things look a little bit more clear to you regarding IPv6 and you understood that this is not an IT network monster of any kind. Let me show you a small example of how you can configure the Cisco interfaces for IPv6 connectivity. Routing and more advanced stuff in a future post maybe.

For this tutorial I will use the same topology like in the previous post, please have a look to it here, but for the IPv6 configuration will only focus on the LAN side, the connection between R1 and R2. There is already a working IPv4 link between this 2 devices. Please click below to see the example:

If for some reasons the tutorial above is not available for you, please check this text file which consist of the configuration needed to enable IPv6 configuration between 2 Cisco devices.

Cisco: Engineer’s trick to avoid suboptimal path

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 a more elegant approach and from the networking point of view more safe considering the complex routing environment. I will use the same topology like in the previous post to offer you the possibility to compare these 2 methods presented and to choose the one that you understand and fit better to your needs. Also there are some other ways to do it and please feel free to discussed them in the comments section and maybe to present them here in a future post.

We will achive the desired results by setting one community on R1 for the advertised network 192.168.82.1 and dropping the prefixes, marked with the same community, on R2. Please be aware that for this method to work you have to allowed BGP peers to send communities list with the command “neighbor xx.xx.xx.xx send-community …” under “router bgp xxx” process.

Please see the example by clicking the image below:

Cisco: Dirty trick to force optimal path in routed environment

Everywhere in the world people try to find the optimal path to achieve something.If we speak about roads, trips and in our case networking, choosing the best path to an end point can have only advantages.

I took the term optimal / suboptimal path from the routing issues that can appear in the OSPF network environment and which are called by the experts suboptimal routing. What I want to explain here, maybe you already seen it, is that in some network environment the best path to a destination is not always preferred by the routing protocol due to some unhappy situations. To understand better what I’m talking here, please have a look at the topology that I will use for this tutorial and for the next one regarding optimal path.

In the example below I will show you a simple and dirty trick how you can escape from this situation. I recommend to use this dirty trick only in urgent cases and only temporary as this can lead to more problems if you have a complex network environment. In the next days I will show you a more elegant method to escape from suboptimal path problem.

As you can see in the topology we have a network environment formed by 4 routers. On R1 we have configured a BGP session with the peer R3 and OSPF with R2. Since the peers are in different autonomous systems the BGP session will be external. For OSPF this does not matter.The Loopback100 interface in R1 is advertised into BGP and OSPF, and it is learned by R2. On R2 the interface 192.168.82.1 arrives on BGP table and OSPF table, but since the Administrative Distance of the eBGP (20) is better that the one of OSPF (110) on the routing table will appear the route through R4. This is bad because without considering the obvious longer path through R4, we can see that the links between R2-R4 and R1-R3 are Serial interfaces and definitely with more limited bandwidth than FastEhernet interface R1-R2 (we assume that we do no have any QoS or other limitation). Last note before we begin, all the routing processes on the devices are completely configured and functional.

Cisco: How to configure simple IP SLA monitor

Before we begin let’s see what is this SLA term, for those of us who are not very familiar with the Service Provider terms. IP Service Level Agreements (SLAs) enable customers to assure new business-critical IP applications, as well as IP services that utilize data, voice, and video, in an IP network. With Cisco IOS IP SLAs, users can verify service guarantees, increase network reliability by validating network performance, pro actively identify network issues assure an easy way to deploy new IP services. Cisco IOS IP SLAs use active monitoring, enabling the measurement of network performance and health.

For the following how-to please have a quick look into the topology. As you can see I have a basic routing topology, imported from another tutorial from FirstDigest, and let’s assume that we want to monitor the line between R1 and TEST-RT. For this we will configure a very simple IP SLA monitor, based on icmp echo packets, which will measure our RTT (Round Trip Time) or latency and provide us with valuable informations. For example in case of VoIP problems we can check the latency and in case of a value bigger than 200 ms (220 ms maximum accepted for the voice service to function properly) we will know from where are the problems generated. Of course IP SLA can have more complex configuration under Cisco IOS (e.g. http or ftp transfer to check if the service provider assure us the bandwidth specified in the contract).

One personal advice from my experience. Even if all the data and information provided by IOS IP SLA monitor can be checked with “show…” commands, I would advice you to get a third party software that can interpret this data for you and draw nice graphs or store them in an archive for you. This kind of software are MRTG, Weathermap, Nagios, RRDtool and others (I put here only the free ones).

Please check the how-to by clicking the image below: