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38 Cards in this Set

  • Front
  • Back
What are the 4 most common uses for route-maps?
* Redistribution
* Policy-based routing (PBR)
What is a big difference between a route-map and an access list?
route maps can modify the packet or route by using set commands
What happens if a route-map statement contain several match statements?
All match statements must be true for for the route-map statement to be considered matched. (A logical AND operation)
What is the purpose of policy based routing?
To let packets take a route other than the obvious shortest path.
What should be documented in an implementation plan when planning route map configuration for PBR?
* Define the route map, conditions to match, action when theres a match
* Which interface the route map will be attached to
What should be documented in an implementation plan when planning route map configuration for redistribution?
* Define the route map, conditions to match, action when theres a match
* Define where the route map will be used to control redistribution
What is the purpose of distribute lists?
To allow an access list to be applied to routing updates
Where is the distribute list configured?
Under the routing protocol process
What factors can distribute lists filter on?
* Incoming interface
* Outgoing interface
* Redistribution from another routing protocol
What should be documented in an implementation plan when planning to configure distribute lists?
* Define traffic filtering requirements that will be used to permit or deny routes, using an access list or a route map
* Define a distribute list to use the access list or route map, and wether it will be applied inbound or outbound
What are the 3 steps to configure a distribute list?
* Identify the network addresses of the routes to filter and create an access list
* Determine if you want to filter traffic incoming or outgoing on an interface, or routes being distributed from another protocol
* Use the distribute-list command to assign the access list to filter outgoing updates
What are some drawbacks to using distribute lists as route filters?
* A subnet mask cannot be easily matched
* Access lists are evaluated sequentially for every IP prefix in the routing update
* A extended access list can be cumbersome to configure
What are some advantages of using prefix lists instead of access lists when doing route filtering?
Significant performance improvement over access lists in loadin and route lookup of large lists.
What are the key issues with redistribution?
* Routing feedback (loops)
* Incompatible routing information, path selection might not be optimal
* Inconsistent convergence times
What are the default seed metrics for these protocols?

RIP 0, Infinity
IGRP/EIGRP 0, Infinity
OSPF 20, 1 for BGP, all E2 (for OSPF to OSPF the metric is preserved)
IS-IS 0, not infinity
BGP BGP metric is set to IGP value
Multipoint one-way only works well if:
- The receiving protocol supports different administrative distances for internal and external routes (EIGRP, OSPF, BGP)
- The AD of the receiving protocols external routers is higher than the AD of the "from"-protocols routes.
How can you prevent loops in multipoint redistribution scenarios?
- Insert only internal routes from protocol A to B (and vice versa)
- Tag routes in redistribution points and filter based on these tags when configuring redistribution in the other direction.
- Propagate metrics from routing protocol A to protocol B properly
- Use default routes to avoid having to do two-way redistribution
What is the safest way of implementing redistribution?
Only one direction on only one boundary router within the network.
(One-point one way)
What are some common network performance issues related to routing?
* Excessive routing updates
* Presence of any route maps/filters
* The number of routing protocols running in the same AS
What are the solutions to common network performance issues related to routing?
* Design changes
* Using passive interfaces
* Route filtering
What techinques can be used to filter routes?
* Distribute lists
* Access lists
* Route maps
* Prefix lists
What are some reasons for running more than one routing protocol?
* Migration
* Host system needs
* Mixed-vendor environment
* Political and geographical borders
What happens to the routing table of the router performing the redistribution?
Nothing, it doesnt change
What are some issues arising when redistributing routes?
* Routing loops
* Incompatible routing information
* Inconsistent convergence times
What are the two methods of one-point route redistribution?
one way and two way
What is a possible issue with one-point one way and one-point two way redistribution?
Suboptimal routing
What are the two methods of multipoint route redistribution?
One way and two way
What is a key issue with multipoint redistribution?
It is likely to introduce potential routing loops
In which routing protocol routing process can you use the "subnets" parameter when redistributing into that protocol?
How can you prevent a routers routing updates from being sent through a specific router interface?
with the "passive-interface" router configuration command
How can the administrative distance be manipulated to influence the route selection process?
With the "distance" router configuration command for all protocols.
What two commands are good to use to verify route redistribution?
show ip route [ip address] and traceroute [ip address]
When configuring route-maps for PBR, which command goes under the interface?
ip policy route map [map-tag]
What can allow an access list to be applied to routing updates?
A distribute-list
What methods can be used to filter routes?
Access lists, route maps, distribute lists, prefix lists
What may be the cause of a routing loop in a network that has redundant paths between two routing processes?
Depending on how redistribution is deployed, routers might send routing information back into a routing protocol.
When configuring a default metric for redistributed routes, should the metric be set to a value larger or smaller than the largest metric within the receiving autonomous system?
Larger, to help prevent suboptimal routing and loops.
What are some applications of route-maps?
* Route filtering during redistribution