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static and dynamic route

jackson_rex asked
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Last Modified: 2011-10-03
what happened when we give static route in one route and dynamic route (rip) in another route. can we do this. is there any routers that doesnt support RARP. if then which is better static route or dynamic route or something else.
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In my opinion dynamic routes are a better for reliability as they will automatically re-configure themselves should a link go down.

Static routes are only really useful for 'stub' networks because of the problems faced through re-configuration should the static link die.


i didn't ask about that!!
can we have both static and dynamic routes in the same router or network.is there any routers that doesnt support RARP. if then which is better, static route or dynamic
route or something else.
Your question is a tad confusing.  I am not quite making the connection between RARP and static/dynamic routes.

Anyway - firstoff you can certainly have both static and dynamic routes on the same router.  This is extremely common.  For that matter, you can have any number of different route types (i.e. static, RIP, OSPF, etc).  Just remember that if you have multiple route sources for a single route, the router will choose one source as the "most trusted".  On Cisco routers this is done with administrative distance - the lowest one wins.  For example, an OSPF route has an AD of 120 and a static has an AD of 2 or 1 (depending on the static type).  Therefore, if you have 1 route with both an OSPF entry and a static entry, the static will win (statics are set up to basically always win).  However, you do have the ability when creating a static route to change the AD for that route to make the dynamic route preferred.  This is called a floating static route.

On the RARP issue, I don't know if there are any that don't support it.  I do know that Cisco routers will attempt to gain an IP address via RARP if you have not given it a static address.  You can see more about RARP here:

Hope that helps.

The previous comment is correct, although I will add that static routes are not advertised by routing protocols such as OSPF, RIP, and EIGRP by default.  You will need to enter the command

router(config)#router EIGRP 1     (or RIP, OSPF, etc.)
router(config)#redistribute static

specify a "floating static route" using the principles listed above:

router(config)#ip route 240

note the higher administrative distance at the end of the statement.  These types of routes are used for backup interfaces, such as BRI lines or Async.  The backup interface will be designated as a passive interface in regards to routing protocol updates.  ex.

router(config)#router EIGRP 1
router(config)#passive-interface bri0

this means the bri interface will only pick up if routing updates or no longer received on the primary link (such as a T1).  We know this, because the router will not elect to use a path with a higher cost normally, only if it is the only one available.  Remember also, that EIGRP and OSPF will load balance accross EQUAL COST LINKS -which is not the case here.  As far as a static being better than a dynamic, it depends.  Static routes can be viewed simply by doing a "show run", while dynamic require a "show ip route" command.  Also, if you are using only static routes, there is no routing protocol traffic on your network.  RIP will broadcast every 30 seconds -other protocols, such as EIGRP will send out hello packets depending on link speed.  

One more note!  If you are using RIP version 1 as a routing protocol, it does not broadcast the subnet mask to neighboring routers -meaning that if you are using complex subnetting techniques such as VLSM or supernetting, you will have inconsistant routing.  Static routes DO send the mask, and are therefore more reliable in this situation.  It should be mentioned that EIGRP and RIP version 2 do send the mask and support VLSM (variable link subnet masks).  You can activate RIP version 2 by typing

router(config)#router rip
       (config-router)#ver 2

this should do it.  feel free to have me clarify any of this.

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