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CCNP ROUTE Study – EIGRP Offset Lists
In certain situations an engineer may need to manipulate EIGRP metrics, and one method is to use Offset Lists to increase both the AD (Advertised Distance) and FD (Feasible Distance) of a route by a...
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CCNP ROUTE Study – EIGRP Stub Routers
Stub Routers in EIGRP have two purposes: to prevent a router from advertising any routes it has learnt via EIGRP to neighbouring routers to limit the scope of query messages when a route goes “active”...
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CCNP ROUTE Study – EIGRP Route Filtering
There are many reasons why you would want to implement route filtering. A good example would be to prevent routes to transit networks being advertised to a branch router, because no host in the branch...
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CCNP ROUTE Study – OSPF adjacency set up
In this post we’re going to take a look at the process of two Cisco routers forming an OSPF neighbour adjacency, with an emphasis on what’s going on at a packet level. We’ll look at the packets sent...
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CCNP ROUTE Study – OSPF Authentication
We know that two OSPF routers will become neighbours if they can agree on certain parameters (see my previous post for details) and this is great, but suppose the bad guys were able to connect their...
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CCNP ROUTE Study – OSPF DR/BDR Elections (and how to rig them….)
When multiple OSPF routers are connected to a multi-access medium such as Ethernet, a Designated Router (DR) and a Backup Designated Router (BDR) are elected. DR’s reduce network traffic as only they...
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CCNP ROUTE Study – OSPF Virtual Links
One of the golden rules of OSPF is that all areas must be connected to the backbone area 0, however sometimes this is not physically possible, and this is where Virtual Links come in. A virtual link is...
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BGP Basics – iBGP and eBGP peering
This is the first post in a mini-series on BGP basics, and looks at setting up internal and external BGP neighbours using loopback interfaces. The advantage loopbacks have over physical interfaces is...
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BGP Basics – advertising networks into BGP
The first post in this BGP mini-series looked at setting up BGP peering between routers. Now we’ll take things a step further and actually exchange some routing information between those peers. Here’s...
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BGP Basics – modifying attributes
The previous post in this series looked at the exchange of routes between BGP peers, and this post takes this a step further by looking at two BGP attributes that can be modified to influence how a...
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