What is the default FSPF cost of a port channel that consists of four 2-Gb/s links, with one link
down because of an error?
A.
500
B.
166
C.
250
D.
125
E.
1000
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Isn’t it ture that the answer suposed to be 1000 since one link is down because of an error?
the remaining 1 Gbps out of 2 Gbps is 1 Gbps that is equal to 1000 as per Cisco documentations!
About FSPF Link Cost
http://www.cisco.com/en/US/products/ps5989/products_configuration_guide_chapter09186a0080662d28.html#wp1161379
FSPF tracks the state of links on all switches in the fabric, associates a cost with each link in its database, and then chooses the path with a minimal cost. The cost associated with an interface can be administratively changed to implement the FSPF route selection. The integer value to specify cost can range from 1 to 65,535. The default cost for 1 Gbps is 1000 and for 2 Gbps is 500.
Please clarify?
Thanks
Toma
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I think the answer is B.166
4links x 2Gb/s = 125
3links x 2Gb/s = 166
2links x 2Gb/s = 250
1links x 2Gb/s = 500
http://ieoc.com/forums/p/30053/244101.aspx
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In reality the cost of portchannel doesn’t depend on the links with UP status. It depends on total quantity of all ports in portchannel (UP and DOWN). In the question total bandwith of all links in the portchannel is a 8Gbit/s. And because of it default cost is 125.
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Is there documentation that clearly explain this?
Thanks
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Correct ans is 125
Here is explanation from Cisco Doc.
Redundant Links
To further improve on the topology in Figure 31-1, each connection between any pair of switches can be replicated; two or more links can be present between a pair of switches. Figure 31-2 shows this arrangement. Because switches in the Cisco MDS 9000 Family support PortChanneling, each pair of physical links can appear to the FSPF protocol as one single logical link.
By bundling pairs of physical links, FSPF efficiency is considerably improved by the reduced database size and the frequency of link updates. Once physical links are aggregated, failures are not attached to a single link but to the entire PortChannel. This configuration also improves the resiliency of the network. The failure of a link in a PortChannel does not trigger a route change, thereby reducing the risks of routing loops, traffic loss, or fabric downtime for route reconfiguration.
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