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specific routes with static default route

Posted on 2014-02-14
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Last Modified: 2014-04-09
I need clarification on the specific routes and default route. The below output is from a sample static routes from a router (this is pointed to the internal network). I see that it has specific routes as well as a default route. Should it be sufficient just to have the static default route pointed to 192.168.200.1? Thx

S*    0.0.0.0/0 [1/0] via 192.168.200.1
S     192.168.0.0/24 [1/0] via 192.168.200.1
S     192.168.1.0/24 [1/0] via 192.168.200.1
S     192.168.2.0/24 [1/0] via 192.168.200.1
S     192.168.8.0/24 [1/0] via 192.168.200.1
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Question by:leblanc
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14 Comments
 
LVL 25

Accepted Solution

by:
Ken Boone earned 1144 total points
ID: 39859419
A specific route will always be chosen first.  In your case all routes go to the same place so in essence all you need is the default route.  The specific routes are unnecessary.
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LVL 26

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by:Fred Marshall
Fred Marshall earned 288 total points
ID: 39859445
While it appears to be sufficient in this case to have the default route only, there are a few caveats:

- depending on the device and its use in context, it may not route private addresses/ranges.

The static default route is necessary for everything else.  Probably hard to get rid of anyway.
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LVL 17

Expert Comment

by:jburgaard
ID: 39859455
I agree with kenboonejr, if there are no 'holes' , fx 192.168.3/24 routed elsewhere, no need for the specific, all included in default.
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Author Comment

by:leblanc
ID: 39859476
The S*    0.0.0.0/0 [1/0] via 192.168.200.1 will send the traffic for any network to the 192.168.200.1. So the rest of the routes are useless. Correct?
The reason I ask is because I see this type of static routing configuration in a lot of routers and I am not sure why you need all that: the default static route, the 192.168.0.0/24, and the specific routes (192.168.x.0/24)
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by:Ken Boone
Ken Boone earned 1144 total points
ID: 39859504
Yes the rest of the routes are useless.  

You see this because a lot of guys just don't have the experience to know what is going on and so they put them in there for good measure ;)
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LVL 26

Expert Comment

by:Fred Marshall
ID: 39859590
I can imagine how such a table would be created automatically:

The default address is not compared with the others (VLANs perhaps?)

So, it just gets repeated.

I don't see any appreciable harm in it.... it's not like routing tables aren't traversed in normal operation all the time.
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LVL 25

Assisted Solution

by:Ken Boone
Ken Boone earned 1144 total points
ID: 39859610
No the routes shown were S - static routes - that means they were manually created.  Any interfaces on a router would have a C - connected routes - those are automatic.

Then if you are running a routing protocol you would have dynamic routes as well.

There is no harm in it, other than taking up space in the table, and longer processing - that you won't notice in the given example, and possibly typos that cause problems, and then routes that people leave in place  when they are aren't needed that causes problems down the road.  My advice is to only put in the routes you need.  It keeps it simple.
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LVL 26

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by:Soulja
Soulja earned 568 total points
ID: 39859611
Are those the only routes in your table? I can see those specific routes being used if you have a more summarized route pointing elsewhere.

For example if you have a 192.168.0.0/16 pointing to a different next hop, yet those specific subnets exist else where.  If that is the case then those statics would be used.
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LVL 25

Expert Comment

by:Ken Boone
ID: 39859773
Yes that would be the true.
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LVL 1

Author Comment

by:leblanc
ID: 39859796
Yes there are other 192.168.x.0 on the other remote locations.  I can understand why you need default static route as you may have other subnets (other than 192.168.x.0) in the internal network. But then you don't need the 192.168.0.0/24 route if you already have specific routes.
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LVL 26

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by:Soulja
Soulja earned 568 total points
ID: 39859817
I am confused by your previous post. Is it a statement or question?

The 192.168.0.0/24 is a specific route.

If you are stating that you don't need a 192.168.0.0/16 if you have specific routes, it all depends. Are those specific routes going the same direction as the summarized route?

What if there are 50 networks behind that summarized route going to say next hop A, but you have 4 odd networks that exist behind hop B. Then you would poing those specific routes to the their respective hop.
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LVL 1

Author Comment

by:leblanc
ID: 39859866
This is what I was referring to:
S     192.168.0.0/24 [1/0] via 192.168.200.1
S     192.168.1.0/24 [1/0] via 192.168.200.1

So if you already have the specific route (192.168.1.0/24), you do not need 192.168.0.0/24. Correct?
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LVL 25

Assisted Solution

by:Ken Boone
Ken Boone earned 1144 total points
ID: 39859876
Well those are actually 2 different networks.  They go to the same place but 192.168.0.0/24 and 192.168.1.0/24 are 2 different networks.

Because you have a default route 0.0.0.0 going to the same location, you do not need either of these routes.

What Soulja was referring to is that if you had a route like 192.168.0.0 /16 going somewhere else, then that would take precedence over the default route, therefore you WOULD need the specific routes to ensure they go where you want them.
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LVL 1

Author Comment

by:leblanc
ID: 39860153
yes. I overlooked that. I was thinking of 192.168.0.0/16. Yes you're correct.
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