- Why would you ever want to summarize routes?
Summarizing routes minimizes the routes advertised to the network. For example, instead of advertising 192.168.0.0/24, 192.168.1.0/24…192.168.n.0/24, a router can advertise a single route to 192.168.0.0/16. Keeping routing tables small saves hardware resources, minimizes convergence times, helps avoid route flapping, and makes the routing table easier to read for humans.
- When will an EIGRP router auto-summarize a route?
If a router has interfaces that that are in different classes of network (Class A, B, C), then that router will auto-summarize those routes up to the classful boundary. For example, if you have a 10.0.0.1/24 and a 192.168.100.1/30, the router will advertise 10.0.0.0/8 and 192.168.100.0/24.
- You have two routers advertising the same summarized route. How do you make one preferred over the other?
Adjust the delay or bandwidth so one is favored.
- What is suboptimal forwarding in regards to summarization?
A summary route could be advertised from a router that’s not in the optimal path to the destination. If that route is chosen by a downstream router, traffic is passed to that router instead of a more optimal path through another router.
- How do you avoid suboptimal forwarding in regards to summarization?
Disable summarization. Advertising real networks will result in the optimal path being calculated.
- How do you manually summarize the route 192.168.100.0/22?
R1(config-if)#ip summary-address eigrp 1 192.168.100.0 255.255.252.0
- When will a summarized route stop being advertised by a router?
When the router no longer has any routes that fall inside the summary route, the summary is removed. That is, if a router is advertising 192.168.100.0/22, the route will be removed if the router no longer has ANY routes that are in the 192.168.10.0 networks.
- What’s the biggest route a router can summarize?
The default route.
- What are two ways to advertise a default route in EIGRP?
Advertise a static default route through redistribute static
Summarize 0/0 out of an interface
- How do you keep one part of the network from having a route to another part of the network?
This is done with route filtering.
- When configuring route filtering in EIGRP, what’s the big keyword?
- What are the three techniques for filtering routes?
- Do you mean to tell me that route filtering also uses ACLs and route-maps?
Yes. Welcome to Cisco Systems.
- How do you use an ACL to filter out the route 192.168.0.0/24?
access-list 1 deny 192.168.0.0 0.0.0.255 access-list 1 permit any router eigrp 1 distribute-list 1 out
- How do you use a prefix list to filter out the route 192.168.0.0/24?
ip prefix-list PL1 deny 192.168.0.0/24 ip preffix-list PL1 permit 0.0.0.0/0 le 32 router eigrp 1 distribute-list prefix PL1 out
- How do you use a route-map to filter out the route 192.168.0.0/24?
access-list 1 permit 192.168.0.0 0.0.0.255 route-map RM1 deny 10 match ip address 1 route-map RM1 permit 999 router eigrp 1 distribute-list route-map RM1 out
ip prefix-list PL1 permit 192.168.0.0/24 route-map RM1 deny 10 match ip address prefix-list PL1 route-map RM1 permit 999 router eigrp 1 distribute-list route-map RM1 out
What Command Was That?
- …shows you the prefix lists configured?
show ip prefix-list
- …shows the summary route being advertised for a particular network?
show ip route 192.168.0.0 255.255.0.0 longer-prefixes
- …shows what networks are being summarizes on a router?
show ip protocols
- …shows what route a router considers to be a default candidate?
show ip route (look for the *)
- …shows the default network?
show ip route