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Differences between default route and last resort route

Hi, I am trying a lab with this topology: https://i.imgur.com/LWbimcx.jpg

in the exercise I am asked to set up OSPF between R1,2 and 3 and Router 4,5 and 6, easy enough.

The lab then asks me this: -Configure a default route on R1 to R4 using the next hop address as argument -Configure a default route (last resort) to the ISP

Now, I was under the impression that default route and last resort, were just two names to describe the same thing. Now however I am puzzled on how should I go about doing that.

I can't obviously set a single default route towards the internet as I do need a way to make the networks behind the router communicate between them, is using static routes to make the routers learn of the networks behind them and then just use a last resort that points to the ISP the way to go or, I am missing something more obvious?

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CCNP|CCDP|CCNA-V|CMNA
3 points · 3 months ago

You're correct in that they're the same thing. I think the lab may be telling you to add a route on R1 pointing to R4 as its default route, and as a separate task configure R4 to have its default route pointing to the ISP.

Original Poster1 point · 3 months ago

Hi and thanks for taking the time to reply, when you say adding a route to R1 pointing to R4 as default route, you mean a static route right?

Now with more Cisco!
1 point · 3 months ago

Any route you add will be static. Any route a protocol adds will be dynamic.

A default route can be either static or dynamic, it just has a prefix length of zero.

CCENT | CCNA
1 point · 3 months ago
  • R1 ip route 160.1.1.2 255.255.255.252 serial 0/0/1

  • R4 ip route 0.0.0.0 0.0.0.0 158.3.5.6

You can't add interface ip address as a static route like you did in first example. Interafce address is next-hop address.

R1 ip route 158.3.5.0 255.255.255.0 160.1.1.2

Now with more Cisco!
1 point · 3 months ago

I was under the impression that default route and last resort, were just two names to describe the same thing

Yes, although they have different flavor. A default route is generally referring to a least-specific route in a route table--that is, a layer 3 device. A default gateway or gateway of last resort is usually referring to the same concept in a host where there are only a few routes: local and last-resort. However, you are correct, they mean the same thing in operation.

I can't obviously set a single default route towards the internet as I do need a way to make the networks behind the router communicate between them

Why are the two concepts exclusive? A default route specifically refers to "everything else". If you can already comunicate between subnets, a default route shouldn't change that.

You might want to review how routes are matched, the concept of most-specificity, and how prefix lengths effect routing tables.

I think what the lab wants you to do is:

  1. Create the default route on R4

    ip route 0.0.0.0 0.0.0.0 <exit interface or next-hop ip addr>

  2. Redistribute the default route from R4 to the other routers in the OSPF domain:

    default-information originate

This saves the extra configuration of having to create default routes on all the other routers. If you just had a few routers its not hard, but what if you had hundreds?

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