Service Provider – Half-Duplex VPN’s
The other day whilst reading up on some SP topics I came across a rarely used function available on some higher end Cisco models called half duplex VRF’s (or HD VRF’s in some places).
I know it is quite a common thing to see in service provider topologies where you have a radius / virtual-template driven platform such as a DSL LNS etc but up until now I wasn’t aware that it can also be used on other platforms on regular (non virtual) interfaces.
For the demo topology I am going to use a faily simple network of three 7200′s in GNS3. According to the Cisco documentation here this feature has been around since 12.4(20)T or 12.2(33)SRC for the SR train.
In the topolgy I am using R1 and R2 to emulate customer sites which will be a member of the same VRF on R3 which will play the role of our PE.
Dynamips server reporting for duty…
Back when I first starting studying for my CCNP I built a rack of equipment to lab things up and practice with (picture below) and after completing my CCNP and moving down the CCIE track (after stopping off for a pit-stop at the CCIP station….) I quickly realised that the rack wasn’t adequate for what I would be needing. There were two options, spend a stupid amount of money and replace the lab with one equal to that of the INE/IPX racks (2811′s, 3745′s etc.) or just scrap most of…
MPLS QoS Marking : The rebuttal
Earlier today Ivan Pepelnjak over at IOS Hints (url / @ioshints) posted a piece on his blog in which he mentioned the behaviour of MPLS QoS markings and how they don’t copy over upon label imposition at the edge-LSR (the post is here). Having only looked at this very same topic a couple of weeks ago I was almost certain that this was not the case, and so I set out to lab it out and either prove myself or Ivan wrong…. My setup for this lab is as follows:
Snippet: BGP as a non-transit AS
In the example below we have three BGP autonomous systems (AS1, AS2 and AS3) each with one router in it. In this example assume that AS3 is a customer of AS1 and AS2 and is multihoming their connection with the two upstream providers for redundancy if one of the providers was to fail. In its default configuration BGP will re-advertise any routes advertised into the AS to all other peers, this means that if route x.x.x.x/24 was advertised to AS3 from AS2 then AS3 would advertise that route back out…
Useful Multicast Addresses
Whilst multicast has been removed from the new CCNPv6 exams this still doesn’t mean you get to escape it, there are several addresses that I sometimes find hard to remember which is which which are detailed below. A lot of the modern routing protocols (RIPv2, EIGRP, OSPF) use multicast over the older method of broadcast (RIPv1) to communicate with adjacent routers/neighbours. This gives the advantage that not all hosts will receive and therefore have to process these packets that are for instance destined for the EIGRP process as they do…
Exam Tip: Learn to count…
Just a quick exam tip for all those people that are studying for your exams. Whilst it may be easy to just open up calculator or jump on over to subnet-calculator.com when you are working out wildcard masks etc. learn to not get into the habit. When you are in the exam room you don’t have access to either of the above so get practising whilst out of the exam room so that you are spending less time on you maths and more time on the questions.
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