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Discussion in 'General Cisco Certifications' started by morph, Mar 20, 2008.

  1. morph

    morph Byte Poster

    So EIGRP uses delay and bandwidth in terms of its metrics. Please excuse my lame questions!

    Is this bandwidth worked out in a way which is dynamic? I suppose what i'm asking is if it looks at the link as say a 30 meg link and that is the bandwidth or does it look at what is actually available ? And (and i think i'm really stretching now) - would QOS come into this at all? in terms of allocation of bandwidth?
    Certifications: Network +, ITIL Foundation, CCENT, CCNA
    WIP: server/ccna security
  2. BosonMichael
    Highly Decorated Member Award

    BosonMichael Yottabyte Poster

    You configure a link's speed with the bandwidth command. The bandwidth is not dynamic; it is a configured value. Similarly, delay is not dynamic; it is a constant value based on the link type.

    If you want to use factors that change dynamically, you can use load and reliability, both of which are calculated values that depend on the performance of the link. By default, these are not used by EIGRP.

    To my knowledge, EIGRP does not use QoS.
    Certifications: CISSP, MCSE+I, MCSE: Security, MCSE: Messaging, MCDST, MCDBA, MCTS, OCP, CCNP, CCDP, CCNA Security, CCNA Voice, CNE, SCSA, Security+, Linux+, Server+, Network+, A+
    WIP: Just about everything!
  3. r.h.lee

    r.h.lee Gigabyte Poster


    It sounds like you may be confusing EIGRP the routing protocol with the routed traffic going through the router. As far as the EIGRP routing protocol that is used in the decision-making process of which routes go into the routing table, there are the default bandwidth values and there are configurable bandwidth values. Within the scope of the CCNA, I think it's important to know and understand that bandwidth is a factor in calculating the EIGRP metric but I don't think you'd actually need to configure a non-default bandwidth value. Since you asked, if you configure the bandwidth value for the interface, it would affect the EIGRP decision-making process of route placement into the routing table and not the actual throughput of the interface. So the bandwidth factor is relatively "static" and not "dynamic" because it's either the default value or a configured value.

    From a "dynamic" perspective, the actual throughput used can be considered "dynamic." Since EIGRP's DUAL process has already been run to build up the routing table, the packets in the router are forwarded based on the routing table. So just like the front door to your home or business may be a single door, a double door, multiple doors, those are like the bandwidth value. However, it doesn't change the actual amount of foot traffic you get coming in and out of the doors.

    EIGRP and basic routing are elements of the Network Infrastructure section of a network. QoS is considered an Intelligent Networking feature. So QoS would affect the routed protocol instead of the routing protocol.

    I hope this helps.
    Certifications: MCSE, MCP+I, MCP, CCNA, A+
  4. morph

    morph Byte Poster

    it does help alot mate!

    its at work were moving to eigrp and i was wondering how that might effect QoS if eigrp was dynamic and if you started messing about with the QoS settings etc.. but all good - its going into the nugget :) thanks guys :)
    Certifications: Network +, ITIL Foundation, CCENT, CCNA
    WIP: server/ccna security

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