Traditional IP routing In traditional IP routing world routing protocols are used to distribute L3 routing information. A forwarding decission is made on packet header and local routing table. Routing lookups are indepedently performed at every hop. Basic MPLS features MPLS is forwarding mechanism in which packets are forwareded based on labels. MPLS can run Full Article…
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CEF
Layer 3 Switch Processing process switching – requires the CPU to be personally involved with every forwarding decission fast switching – still uses a CPU but after a packet has been forwarded, infromation about how to reach the destination is stored in a fast-switching cache CEF – optimizing the router to make it able to Full Article…
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Understanding VPN models
VPN services can be offered as two major models: Overlay model service provider provides virtual point-to-point links between customer sites Frame relay, ATM, X.25, IPSEC, GRE In overlay model SP dont know anything about customer routes! He doesnt participates in customer routing. He doesnt receive any customer routers. He decide how to proceed the packet Full Article…
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Introducing to Modern SP networks (VPN)
Traditional Router-Based networks traditional router-based networks connect customer sites through routers connected via dedicated POINT-TO-POINT links (leased lines) Leased lines advantages complete secure, high bandwidth, superior quality, reliable Leased lines disadvantages Expensive Permanent physical connection not scalable – it is very difficult for SP to provide separate physical connection for every customer sites. VPN networks Full Article…
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BGP authentication
BGP supports authentication mechanism using MD5 mechanism. When authentication is enabled every TCP segment belonging to BGP session is verified and accepted only if the authentication match. If authentication fails, the BGP relationship is not established. You may configure BGP authentication with the command #neighbor {IP address | peer group name} password {XXX}
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BGP troubleshooting basic issues
Active neighbor It may happen that your neighborship is in state Active or Idle. It means that router has sent an open packet and is waiting for response. There could be several reasons for that: neighbor is peering with a wrong IP address neighbor doesnt have neighbor statement for this router AS number is missconfigured Interface Full Article…
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BGP Loop prevention
In BGP there are two loop prevention mechanism: for EBGP there is AS-Path attribute which states that router will drop BGP advertisement when it sees it own AS number in AS path attribute for IBGP there is split horizon rule which states that update sent by one IBGP neighbor should be not send to another Full Article…
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Basic BGP configuration
Configuring BGP routing protocol #router bgp {AS no.} #network {network ID} mask [subnet mask] – When you dont put mask the router will assume default classfull mask #neighbor {IP address} remote-as {AS No.} BEWARE!! In BGP there is rule that states: router looks exactly what you type in network command with the mask also! If Full Article…
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Understanding BGP neighbors
BGP neighbors are routers forming TCP connection for exchanging BGP updates. They are also called BGP Peers or BGP Speakers. There are two types of BGP relationship: IBGP (Internal BGP) EBGP (External BGP) BGP Databases Neighbor table a list of all configured BGP neighbors neighbor has to be manually configured using neighbor command we have Full Article…
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BGP options on Internet
Single homed site a site with a single connetion to ISP is called single homed either use static routes, or advertise the site routes to the ISP and receive default route from ISP when customer is connected to SP via static routes, traffic from that customer on Internet is indistinguishable from traffic from the ISP – Full Article…
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BGP basic information
BGP Autonomous Systems An AS is a collection of networks under a single technical administration IGP operates within an AS BGP is used between ASs Exchange of loop-free routing info is guaranteed BGP features Open standard Exterior – designed for Inter-AS Domain Routing Designed to scale huge inter-network like Internet classless (supports VLSM, CIDR, auto Full Article…
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