BGP and MPLS exam

I've bitten the bullet and scheduled the MPLS and BGP exam for tomorrow. I've really spent way more time tinkering with BGP in the last week than I have with MPLS. That's probably more of a reflection of where my current interest is than what I need to know for the exam. I am happy with what I know about BGP now (I'd call it almost CCIE level knowledge). The MPLS study that I have done over the last week has been mainly focussed on the MPLS VPN and basic MPLS subjects. I did a final read through of the ATM subjects in the Fundamentals book earlier in the week (I know that is a bit of a weak spot in my knowledge). I haven't really studied AToM and VPLS that much in the last week, I don't really know them in depth but I am happy that it will be enough for the exam.

The things I KNOW I need to remember for the exam are:

• You need to be able to route to the IP address used for the router-id by LDP in order for an LDP session to establish (I keep reminding myself and forgetting when I lab something up)
• The different VPN types and overlay, peer-to-peer, extranet etc.
• BGP route selection process (really happy I know my stuff for this)
• Configuring VRFs and using multiple route-targets to allow overlapping and other types of VPNs.
• Using OSPF between the CE and PE routers (sham links are something I spent a while playing with on dynamips)
• Confederations, Route reflectors and how they impact BGP advertisements.
• BGP attributes and how to change them and what they REALLY do
• Multi-protocol BGP - address-family vpnv4 and address-family ipv4 vrf and what to put under each

I am sure there will be some general MPLS and LDP type questions (ie what tag would router x use to forward a packet, how does the icmp packet too big get delivered, how does LDP find neighbors etc). I am pretty happy I have that sorted.

I'd have to say once I had done an initial read of a few books I got the biggest value from using dynagen / GNS3 labbing things up and using wireshark to look at packets. I really understood HOW LDP worked once I saw the packets. The book didn't really say why LDP used a UDP stream and a TCP stream. After seeing it the UDP stream is just for hello packets and finding a neighbor via multicast. The TCP stream is for advertising labels (using the LDP router-ids for the source and destination). Why couldn't the Fundamentals book just say that?

The other thing I am always slipping up on is BGP neighbor establishment. I have a habit of mistyping IP addresses, mistyping AS numbers or forgetting eBGP multihop. I tend to struggle for a while and turn on debug ip bgp and then just recheck my configurations. I keep forgetting how powerful the show ip bgp neighbors command is.