Link-State Protocol

I am a bit confused on how this works. How does it determine the best route? Here is a copy of a table:

Route Location in Figure 8-16 Cumulative Cost
R1–R7–R8 Left 10 + 180 + 10 = 200
R1–R5–R6–R8 Middle 20 + 30 + 40 + 10 = 100
R1–R2–R3–R4–R8 Right 30 + 60 + 20 + 5 + 10 = 125

The book states that the path would go down the middle (next hop R5). why would it choose this route and not the R7 hop? it only has one router to go through to get to the subnet?

And how does it determine the cost? For example:
first line.
R1 cost 10 (the first router)
R7 cost 180 (second router)
R8 cost 10 (destination router)

Thank in advance

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Comments

Netwurk

troyt93955 wrote: »

I am a bit confused on how this works. How does it determine the best route? Here is a copy of a table:

Route Location in Figure 8-16 Cumulative Cost
R1–R7–R8 Left 10 + 180 + 10 = 200
R1–R5–R6–R8 Middle 20 + 30 + 40 + 10 = 100
R1–R2–R3–R4–R8 Right 30 + 60 + 20 + 5 + 10 = 125

The book states that the path would go down the middle (next hop R5). why would it choose this route and not the R7 hop? it only has one router to go through to get to the subnet?

And how does it determine the cost? For example:
first line.
R1 cost 10 (the first router)
R7 cost 180 (second router)
R8 cost 10 (destination router)

Thank in advance

I guess you're talking OSPF, so hopefully this link will help

Dynamic Routing Protocols > Link State Routing Protocols

We use EIGRP at work or I would try to be more helpful than just posting a link. Although I'm going to have to relearn OSPF (in depth) for the ROUTE exam so give me a couple of months and with any luck I might be an expert by then.

hypnotoad

RIP (and RIPv2) take hop count (and only hop count) in to account, so the R7 path would win in RIP.

EIGRP by default uses least bandwidth and cumulative delay as factors, so assuming those costs are in your example, the cost of 100 is the lowest.

OSPF uses a bandwidth calculation by default, so once again, 100 is the lowest even though it has more hops.

troyt93955

Very cool, thanks. Let me know how that Route test goes. I just ordered the books this week.

stuh84

Yep think of it like going through two routers/hops with gig links, or one router/hop with a fast ethernet link. RIP thinks the fast ethernet is better, OSPF thinks the gig links are better.