CCNP - Questions...route maps...

Author

Questions...route maps...

cnet_designer

2003-05-05, 5:12 pm

Can someone tell me what is the effect of the implicit deny in the end of route map? i found in cisco website,, that if the packet didn't match and reached the implicit deny, then it will be routed in normal fashion... and won't be discarded... what do you think?

Another thing, is there a difference between Configuring the route map and applying it..? i found that applying the route map should be over incoming interfaces..so configuring it is the same? or what,,,?

Riverwind6

2003-05-07, 8:20 am

You use a route map to change the normal routing behaviour. You could put a route map that says "If the packet comes from this host, then use this route to send it". Then in the route map statements, you just put the source host and where to send it. If the packet doesnt come from that source host, it will reach the implicit deny any and will be routed in normal fashion(using the routing table like usual) versus being discarded.

Yankee

2003-05-07, 10:12 am

In the most basic sense the rule is that if there is no match in the permit statements the packet will be normally routed. A match on a deny statement will also cause the packet to be normally routed.

There is no real need to even think about an implicit deny.

Yankee

SureshHomepage

2003-05-09, 7:50 pm

Hi,
Route maps are used(called?) in conjunction with policy routing commands and redistribution commands.

Routemaps with policy routing deals with just packets whereas redistribution influences the 'routes'.

As you guys are aware, policy routes are nothing but static routes with a difference is that static routes forward packets based on the destination address of the packet whereas the policy routes forward a packet based on the source address of a packet.

If a route map is being called by a redistribution command and a routing matches a statement with deny action, the route will not be redistributed. On the other hand if a route map is being called by a policy routing command and a packet matches a statement with deny action, the packet will be forwarded as normal using the normal routing process.

Coming to your question, an implicit deny exists at the end of every route map. Routes that passes through a redistribution-route-map with no match are not redistributed. But packets that pass through policy-route-map with no match are sent to the normal routing process.

Hope this would help.

Sponsored Links