July 2011

CCNP Notes: Advanced IGP Redistribution

What can a route-map perform?

  • Identify the subset of the routes to filter or change based on the route’s prefix/length, plus other factors
  • Make filtering choices about which routes are redistributed, and which are not
  • Set the metric to different values based on information matchable by the route-map
  • Set the type of external route for different redistributed routes, for example, OSPF Type 1 for some routes, Type 2 for others
  • Set a route tag, a unitless integer value that can later be matched with a route-map at another redistribution point

How do you configure a route-map with redistribution?

Redistribute command has two mechanisms that allow filtering of routes:

  • the match {internal | external 1 | external 2 | nssa-external} parameters
  • the route-map map-name option
router eigrp 1
redistribute ospf 2 route-map FILTER-OSPF-ROUTES

How do you configure route filtering with Redistribution?

Use a route-map that has a deny clause to filter routes or a permit clause to not filter routes. Within the route-map you can match routes by using standard and extended ACLs with a deny clause to filter routes & use a permit clause at the end that matches all the remaining routes that allows them to go through.

An alternative is to use IP prefix lists within a route-map with a permit clause so that routes are allowed. Use the implicit deny all at the end of the route-map to filter denied routes.

What commands are used to verify redistribution filtering operations?

Use the show ip route network command on the router that is to have filtered routes. The filtered routes should not be in the routing table. Also, additional routes should not be filtered. You can also verify this in the topology table of the router.

Any ACLs or prefix lists used to filter routes can be verified by using the show ip access-list [number | name] and show ip prefix-list detail [name] to show an increment in the counters of the filtered routes.

How would you configure metric settings when redistributing?

Utilize the set metric command within the route-map. For EIGRP there are five parameters (bandwidth, delay, reliability, load, mtu). For OSPF and RIP there is only one integer metric. Example:

route-map route-map-name permit 10
match ip address prefix-list prefix-list-name
set metric 1000 44 255 1 1500

What command is used to verify metric settings?

In EIGRP:

show ip eigrp topology network

When redistributing, how would you set the external route type?

Used when redistributing into OSPF. Utilize the set metric-type route-map subcommand:

set metric-type {type-1 | type-2}

What is a distribute-list?

A distribute-list is a method of filtering routes, similar to a route-map, except it is used if you do not need additional functions supplied by the route-map. You can filter routes with an ACL or prefix-list. It also refers to the direction and the routing process in which the updates are received with an in or out referenced in the distribute-list.

Syntax:

distribute-list 1 out ospf 2 or distribute-list prefix UPDATES out eigrp 1

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CCNP ROUTE Notes: IGP Redistribution

What is Path Control?

It is a class of tools and protocols that Layer 3 devices use to learn, manipulate and use IP routes.

Why would you use Route Redistribution?

Route redistribution is used when the domain is using more than one routing protocol. An example is in the event of a merger. One company can be using OSPF and the other EIGRP. To share each others’ routes, redistribution of the routing protocols in both directions would be necessary. Redistribution is needed when routes from both routing protocols need to be shared.

What is the concept and process of redistribution?

In redistribution, at least one router must:

  • Use at least one working physical link with each routing domain
  • A working routing protocol for each routing domain
  • Additional redistribution configuration on each routing protocol, using the redistribute command.

The concept is that a router between two routing domains will use the redistribute command to take routes from each routing domain and include them in the other. The redistribute command takes the routes from the IP routing table, connected interfaces and passive interfaces and redistributes them into the other routing domain.

What command is used to redistribute EIGRP?

redistribute protocol [process-id | as-number] [metric bw delay reliability load mtu] [match {internal | nssa-external | external 1 | external 2}] [tag tag-value] [route-map name]

What does a baseline configuration of EIGRP redistribution look like?

Example: redistributing EIGRP routes into OSPF and vice-versa. On the router between both routing domains:

RD1# config t
! Redistribute OSPF routes into EIGRP
RD1(config)# router eigrp 1
RD1(config-router)# redistribute ospf 2
RD1(config-router)# end
RD1# config t
! Redistribute EIGRP routes into OSPF
RD1(config)# router ospf 2
RD1(config-router)# redistribute eigrp 1
RD1(config-router)# end

How do you verify EIGRP redistribution?

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Frame Relay Operations

Some of my notes from the CCNP OCG.

What are some IP subnetting designs for Frame Relay?

Designs include one subnet for all PVCs or one subnet per PVC.

What are some challenges of OSPF over multipoint?

By default, OSPF needs more configuration for correct operation over Frame Relay. Issues include neighbor discovery, Designated Router selection and mapping. For neighbor discovery to work, actions must be taken based on the configurations:

  • If network type allows neighbor discovery & InARP, neighbors will be discovered.
  • If network type allows discovery and frame-relay map is used, configure with broadcast keyword.
  • If network type doesn’t allow neighbor discovery, must statically define neighbors.

How are neighbors defined?

With the neighbor router subcommand.

What mapping issues occur with a partial mesh?

DR & BDR are chosen depending on network type. Issues will arise on partial mesh networks because of connectivity to DR or BDR. In conclusion, if requiring the use of a DR or BDR, ensure that both have a PVC connection to each router. Or configure the network type to avoid DR/BDR usage

To resolve Partial Mesh mapping issues, ensure that a router lists each other routers’ DLCI used to reach that router. Problem occurs when using InARP or static frame-relay maps. Those without a direct PVC need a static IP to DLCI mapping.

How do you configure OSPF Frame Relay?

To configure OSPF over Frame Relay, you need to know if using more than two routers. If so, decide on physical or multipoint interfaces. Then decide if routers should elect a DR/BDR. This will determine the network type.

What and how is Point-to-Multipoint used?

Point-to-multipoint is opposite of non-broadcast. DR/BDR are not elected and neighbors are dynamically discovered. Routers are configured with a network type ip ospf network point-to-multipoint interface subcommand. Frame Relay maps are required if partial mesh exists.

Point-to-Multipoint configuration:

neighbor next-hop-IP [cost cost-value] [priority priority-value] 

How do you verify Frame Relay on OSPF?

With command:

sh ip ospf interface

What is Point-to-Multipoint non-broadcast?

Doesn’t elect a DR/BDR and doesn’t dynamically discover neighbors. Therefore, frame relay map needs to be configured for partial mesh network and neighbors must be defined with a neighbor command.

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