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Hello, I am oblivious on what cables are to be used on the serial and fast ethernet interfaces on a cisco 2811.

I need to know what types of available cables with their respective link speeds are available for my configuration of an ospf routing protocol.

I just usually configure my OSPF with disregard to the link speeds but for my final project in school I am required to use variable link speeds on all of my serial and fast ethernet links.

So please help me by telling me what are the available links that I must use on the interfaces of this device. I was considering T1 because my professor usually always mentions that but I don't have the rationale behind that :(

I looked up in this site for guidance but I can't fathom how I should I apply this to my topology and ultimately in the configuration of the bandwidth for each of the interfaces in my routers and switches.

Thank you! :D

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  • Latest Post Latest Post by m_buzuzima
Member Avatar for m_buzuzima

Hi,

There is multiple links as there is multiple interfaces a router can support. The reason why you are been asked to used different link is that each link has its own speed, for example if you take an ethernet cable the speed is 10Mbps and if you take a fastethernet cable the speed is 100Mbps, and this can play a very important role when you are trying to configure OSPF, because OSPF use for his metric Cost which is calculated by this formula: 10^8/Bandwidth in Bps (100.000.000/Bandwidth in Bps), so more higher the bandwidth is better is the cost, because lower cost is better than higher one lol... This mean you can tweak the way OSPF select a path by changing the bandwidth of the link, so let say you have a 100Mbps link in your topology and OSPF selected that path as the best one to put in the routing table, but you wish OSPF to
take another path instead one way to do that is to go to the interface configuration mode and change the bandwidth of the link by using the bandwidth command.
Here are some default OSPF interface costs for common interface speeds:
56kps = 1785
T1 line = 64
Ethernet = 10
16 Mbps = 6
100 Mbps = 1
You can cross check it using the formula I gave you at the top.

Hope this help you in your lab.

commented: Thanks for the detailed information! +2
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