EIGRP Distance Vector Route Discovery

April 27, 2014

EIGRP’s route discovery process uses a “routing by rumour” approach. Meaning that the routers in an autonomous system heard about their routes from another autonomous system/router, they did not receive the route information first hand.This essentially means the routers heard about the routes by listening to network gossip.

The information collected is stored in the following tables.

  • Neighbour Table
  • Topology Table
  • Router Table

With this EIGRP will calculate the best paths and any redundant links (if available) using the following:

  • Bandwidth
  • Delay
  • Load
  • Reliability

MTU is sometimes reffered to being used but it in fact is not, it is only used for some commands but doesn’t affect the outcome of the formula.


Reliable Transport Protocol (RTP)

April 16, 2014

This is a brief rundown of RTP and how it is used by EIGRP for reliable communication.

  • Proprietary Protocol
  • Used and relied on by EIGRP for reliable packet delivery to neighbours.
  • Manages inter EIGRP router communications

So EIGRP uses the multicast address 224.0.0.10 and each time a multicast is sent, it is recorded and awaits a reply of receipt. If and when the multicasts fails, EIGRP will switch to unicast packets and continue to await a reply. If there is no response after 16 attempts, that neighbour is declared dead.

So any information these routers send between neighbours is tracked and tagged with sequence numbers, this allows the routers to identify:

  • Old
  • Out of order
  • Redundant Information

Types of IPv6 Addresses

April 13, 2014

There are alot of new terms and techniques that are needed to be learnt in order to get a grasp of the IPv6 principles and as promised i will go over the types of IPv6 addresses that exist. The one that doesn’t exist anymore is the broadcast. Anyway they are:

IPv6 Multicast

  • First 8Bits are 1
  • or FF00::/8

This works just like the IPv4 brother and is used to send traffic to a subset of devices, it also functions, at times, like a broadcast. In the new IPv6 world there is no such thing but the multicast addressing does the same thing.

 

Unspecified

  • Devices use this IPv6 address to ask for an IPv6 address from a DHCP server
  • Written as ::/128

Does as described, before a device has an IP it will use the ::/128 IP as the source and when a DHCP server responds to the request an unused IPv6 address will be assigned.

 

Loopback

  • Performs the same functions as 127.0.0.1 does in IPv4
  • ::1/128

This address is used basically to troubleshoot and test the IP stack on devices.

 

Link Local

  • Every device will generate a link local address
  • Only used to communicate on the local broadcast domain, meaning it won’t pass a router or the Layer 2 link.
  • Written and identified by FE80::/10
  • Link-Local address are generated using the EUI-64 rules aka Stateless Address Auto-configuration (SLAAC)

The link-local address is quite unique and as stated above it will not be used outside the broadcast domain, so without any configuration at all you should be able to connect devices on the same broadcast domain and have connectivity using the Link Local addresses. It’s a pretty cool feature of IPv6 and something to look out for too.

 

Global

  • Can be routed via the internet and between networks
  • Reachable by routers globally
  • 2000::/3 – First 3Bits must be 001
  • AKA Global Unicast Address

Basically this is the address that your local RIR or ISP will allocate to you to use,  without going into details you would be given a further subdivided piece of the above address space to use to connect to the internet. Once this is setup and configured you will be reachable by other routers globally.

 

Anycast

  • Allow the use of the same IP addresse in different locations
  • Function like Global IPv6 Addresses.

The Anycast feature of IPv6 can be used to allow the use of identical IPv6 addresses in different locations. The reason for this is so that you can setup servers for almost anything and the requesting host will find the destination which is closer, not just via metric but this could mean physically too.


IPv6 – The Lowdown

April 7, 2014

IPv6 – Why and When

So what is IPv6, why do we need it and what is it good for ?

It was anticipated back in the 80’s that we would one day run out of IPv4 address’s and the IANA ran out of IPv4 allocations on Jan 31st 2011. This is why IPv6 was developed, it is the successor to IPv4.

We all know that IP, a network layer (Layer 3) protocol is used for logical addressing, so without an IP address any attempt to access services or devices outside your local Broadcast Domain (Layer 2) would prove unsuccessful. With IPv6 now becoming more prevalent in todays networks and the fact Cisco now covers it in the ICND1 exams, it’s a sure sign that it’s time to move with the times. Not only is IPv6 a more efficient protocol, (as we have learnt from IPv4) is also has some cool features which are included within the protocol itself (IPsec being one).

So what’s changed ? , well the most notable is the length of the address and instead of using decimal numbers to represent the address, IPv6 makes use of Hexadecimal to represent it. Each HEX value is worth 4bits and with now 8 groups of 4 hexadecimal values we have increased from a 32Bit addressing system to 128Bit. This means that we now have 3.4×10^38 IPv6 addresses available (Goodluck pronouncing that), this means for any foreseeable future it is very unlikely that we will run out of addresses to use (But they did say who would ever need more then 4kb of storage).

IPv6 Addresses

An Example IPv6 would look like so: FE80:0003:AC33:1111:1200:ADFF:FE43:00D4 (For those keen eyed readers, yes it’s a link local address)

Like IPv4 where we use subnet masks to represent a host and network portion, the same goes for IPv6. a /64 “mask”, using the above example, would mean it is in the FE80:3:AC33:1111 – network. with the other 64bits available for host addressing.

Address Condensing Rules

If you noticed that above i wrote the second group of hex digits as :3 instead of :0003, this brings me to the following rules to condensing an IPv6 address down, cause they are just so damn long now. Anyway they are:

  • Leading Zero’s can be dropped – eg 00AB:6500 can become AB:6500
  • Double Colons can represent one or more groups of zero’s but it can only be used once – eg 1234:0000:0000:4567 becomes 1234::4567
  • To iterate the above rule, you can only do this once, as the router/computer is expecting 8 groups of hex, it will be confused if we use more then one set. As it won’t know how many groupings each double colon represents.

 

My next posts i will go into detail about the type of IPv6 addresses and something called EUI-64. Check out my twitter if you want to get a peek at what it is. @networkinggahan (Twitter)


EIGRP – Enhanced Interior Gateway Protocol – The Basics

April 1, 2014

EIGRP Notes:

  • Reffered to as a hybrid routing protocol or advanced distance vector routing protocol within some documentation
  • Supports VLSM and route summarisation
  • Cisco proprietary protocol
  • Includes Subnet mask in routing updates

 

EIGRP supports the following features.

  • IPv4 and v6
  • Classless
  • VLSM and CIDR
  • Summarisation of networks and discontiguous ones
  • Uses Reliable Transport Protocol (RTP)
  • Path selection is via Diffusing Update Algorithm (DUAL)
  • No broadcasts

The following three values must match between EIGRP enabled routers before they become neighbours and then they can share routes.

  • Reception of either a Hello or ACK
  • Autonomous System Numbers
  • Same K Values

The Hello timer by default is set to 5 seconds, the Hello message is used to establish neighbour relationships with other routers. The Hellos will alert other routers, also of new routers on the internetwork. This also means that when the Hello messages stop, the neighbour relationship will stop.

This brings me onto the Hold Timer, this timer is used to tell the router the time frame it should wait to receive a Hello from a neighbour before it declares that router dead. Once that happens it will be removed from the neighbour table and any routes which used that now dead router will have their paths recalculated.


STP Overview Video

December 12, 2013

Below is a short overview of STP and how to navigate it in the CISCO IOS enjoy.

[youtube=http://www.youtube.com/watch?v=zapAZRP7mEk&w=560&h=315]


Open Shortest Path First (OSPF)

December 12, 2013

Moving forwards the next bunch of topics on the list look like so:

Configure and Verify OSPF

  • Neighbour Adjacencies
  • OSPF States
  • Discuss Multi-area
  • Configure OSPFv2 and v3
  • Router ID
  • LSA Types

So lets first get a little background on OSPF before moving any further.

OSPF or Open Shortest Path First is, as the name suggest, an open standard link state routing protocol. The AD of OSPF is 110 and OSPF uses a metric of the outgoing interface Cost to determine the best route. It’s a fast converging and flexible routing protocol which also enables us to separate the topology into areas.

The Topology data for the OSPF network is contained within Link State Advertisements and all routers in the same area share the exact same topology information.

I won’t delve any further into OSPF at this point, i just simply want to introduce the upcoming topics and as you can see there are a few things to get through. So in the upcoming days i will describe the purpose of the LSA’s the RID , configuration and some helpful troubleshooting commands.

Don’t stress too hard this stuff is pretty easy.


Split Horizon

December 9, 2013

The next routing protocol feature to talk about is Split Horizon.

A feature of Distance Vector that prevents routing loops from forming. Split horizon rules stop a router from sending routing updates back out the interface from which it learnt them from.

Split horizon is used with RIPv2 and EIGRP and yup you guessed it they are Distance Vector routing protocols.

The example below gives you some understanding of what Split Horizon is actually doing. The RIP update going out R1’s FA0/1 interface only includes the subnet 192.168.0.0/24 (Route highlighted in red). As you can see from the routing table below, R1 learnt this network from an update off FA0/3, so Split Horizon Rules allow this network to be sent in an update out FA0/1.

The routes highlighted in black, are learnt from FA0/1 so Split horizon rules will not allow these routes to be sent in an update, over FA0/1

Split_Horizon


Default Administrative Distances

December 1, 2013

The ICND2 exam asks for knowledge about Routing protocols and their Default Administrative distances. The following table below should be burned into your brain before taking the exam i would imagine.

An Administrative Distance is used so a router can make a decision on how believable the route is as reported by the corresponding routing protocols. Learn this and in the coming days we will use this to configure and Verify both flavours of OSPF and EIGRP.

Route Administrative Distance
Connected 0
Static 1
BGP (External Routes) 20
EIGRP (Internal Routes) 90
IGRP 100
OSPF 110
IS-IS 115
RIP 120
EIGRP (External Routes) 170
BGP (Internal Routes) 200
Unusable 255

Power On Self Test (POST)

November 28, 2013

The next item on the agenda for studying towards the ICND2 is the Power On Self Test or POST.

POST is the first thing to run when you first turn on a Cisco Router, stored and run from ROM, the POST tests the serviceability of the routers components. One example that is often described is that POST checks to see if the interfaces are fully functional.

Once everything checks out, the router will then continue with loading the bootstrap.