Member Avatar for ticktock

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 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

  • 2 Contributors
  • 1 Reply
  • 413 Views
  • 1 Week Discussion Span
  • Latest Post Latest Post by m_buzuzima

Dani AI

Generated

Short summary and practical plan (building on and ): the Cisco 2811 has two onboard 10/100 RJ‑45 FastEthernet ports and accepts WIC/HWIC/NM interface cards for extra Ethernet or serial/T1/E1 ports. For FastEthernet use ordinary Cat5/Cat5e patch cables (or HWIC FE modules if you need more ports and auto‑MDIX). For WAN serial links you pick the interface card that matches the service: channelized T1/E1 HWICs (RJ‑48C), DSU/CSU HWICs, or multiprotocol serial HWICs that take V.35/RS‑232/X.21 cable assemblies — buy the Cisco cable that matches the card. (cisco.com)

How to create “variable link speeds” for OSPF labs (two usable approaches):

  • Change the actual line speed on serial lab links (back‑to‑back DCE/DTE or an integrated DSU/CSU). On a DCE serial interface you set the clock rate; that sets the real serial speed.
  • Or change what OSPF sees without touching physical speed: set the interface bandwidth (value is in kbps and is an informational parameter used by routing protocols) or explicitly set ip ospf cost on the interface. Note: bandwidth does not throttle traffic — to enforce throughput limits use shaping/policing (MQC). Example IOS skeleton (use real values for your lab): 
interface Serial0/0/0
 encapsulation ppp
 ip address 10.0.0.1 255.255.255.252
 clock rate <bps>        ! only DCE side, sets real serial speed
 bandwidth <kbps>        ! tells routing protocols the link capacity
 ip ospf cost <n>        ! optional explicit OSPF override

interface FastEthernet0/0
 ip address 192.168.1.1 255.255.255.0
 bandwidth <kbps>

See Cisco docs for the clock rate and bandwidth behavior and for OSPF cost/auto‑cost controls. (cisco.com)

Practical picks and cautions: choose a mix (low‑speed serial, fractional leased channels, full T1/E1 with HWIC DSU, and FastEthernet) so OSPF sees distinct metrics. Use Cisco HWIC‑1DSU/HWIC channelized cards for real T1/E1 lines (RJ‑48C). Always confirm DCE/DTE when you expect to use clock rate, and verify with show interfaces and show ip ospf interface after changes. When you need the router to actually limit throughput (not only change OSPF metrics) use QoS shaping/policing instead of only changing bandwidth. (manuals.plus)

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
Be a part of the DaniWeb community

We're a friendly, industry-focused community of developers, IT pros, digital marketers, and technology enthusiasts meeting, networking, learning, and sharing knowledge.