Cisco Route - Eigrp, Set 2

Front 1

What two metrics does EIGRP calculate for every route?

Back 1

1. Feasible Distance (FD)
2. Reported Distance (RD)
RD is also known as Advertised Distance.

Front 2

What two commands display the metric details for a route?

Back 2

1. #show ip eigrp topology <network/mask>
2. #show ip route <network>

Front 3

What are the commands (and units) to set bandwidth and delay on an interface?

Back 3

#bandwidth (units of Kbps)
#delay (units of tens-of-microseconds)

Front 4

What are the default delay values for FastE, GigE, and Serial?

Back 4

FastE = 100
GigE = 10
Serial = 2000

Front 5

What are the default values for the EIGRP metric weights?

Back 5

K1 = K3 = 1
All others zero.

Front 6

Why should EIGRP metrics K2, K4, and K5 be left at zero?

Back 6

Because load and reliability change over time, which causes EIGRP to reflood topology data and may lead to route flapping.

Front 7

What are the valid values for an EIGRP K-value?

Back 7

Any integer, 0 to 255.

Front 8

What is the purpose of an EIGRP offset-list?

Back 8

Adds a value to the calculated metrics -- both FD and RD -- for matching routes.

Front 9

What is the mode and syntax to configure an EIGRP offset-list?

Back 9

Create a standard ACL w/ permit statement(s)
EIGRP configuration mode
#offset-list <acl> {in|out} <offset value> <interface>

Front 10

What is the EIGRP feasibility condition?

Back 10

If a non-successor route's RD is less than the FD, the route is a feasible successor route.

Front 11

What is an EIGRP successor?

Back 11

The route with the lowest feasible distance (FD).

Front 12

What CLI command will list only successor and feasible successor routes?

Back 12

#show ip eigrp topology

Front 13

What CLI command will list all possible routes, including those that are not feasible successor routes?

Back 13

#show ip eigrp topology all-links

Front 14

What happens when a successor route fails and a feasible successor exists?
What is the convergence time?

Back 14

The router places the feasible successor into the routing table.
Convergence is typically less than 1 second.

Front 15

What is "going active" for an EIGRP router?

Back 15

If the successor route fails and no feasible success exists, the router "goes active" to find an alternate route. Otherwise, the router remains passive.

Front 16

What happens when an EIGRP router goes active?

Back 16

1. Change state in topology to active.
2. Send EIGRP QUERY messages (prefix/length) to every neighbor except the one with the failed route.
3. If the neighbor has a passive route for prefix/length, it responds with a REPLY message and does not forward the QUERY
4. If the neighbor is active for the route, it floods the QUERY to its neighbors
5. When a router recieves a REPLY for prefix/length, it will reply to its neighbors
6. When a router receives a REPLY for all its QUERY messages, it may use the best of the routes.

Front 17

How can an engineer avoid the EIGRP "active" query process?

Back 17

Make sure every route has an FS.

Front 18

What is an EIGRP stub router?

Back 18

A router that should not forward traffic between two remote EIGRP-learned subnets.
#eigrp stub (router eigrp mode)

Front 19

What are the #eigrp stub command options?

Back 19

1. connected - advertise connected routes for interfaces matched with #network
2. summary - advertise auto-summarized routes or statically configured summary routes
3. static - advertise static routes, if #redistribute static is configured
4. redistributed - advertises redistributed routes if redistribution is configured
5. receive-only - does not advertise any routes.

Front 20

EIGRP - How can summary routes help limit QUERY scope?

Back 20

If a router receives a query for a prefix/length and does not have an exactly matching route, but does have an appropriate summary route, the router immediately sends a REPLY and does not flood the QUERY.

Front 21

How does EIGRP deal with "stuck in active" routes?

Back 21

1. Active Timer (3 minutes by default)
2. Halfway through active timer, send an SIA-QUERY to neighbors that have not responded
3. Receive an SIA-REPLY, keep waiting
4. No SIA-REPLY, fail the neighbor relationship

Front 22

How do you configure EIGRP load balancing?

Back 22

EIGRP subcommands:
1. #maximum-paths <n> (default: 4)
2. #variance <n> (value from 1 to 128)

Front 23

What are the EIGRP rules for adding load-balancing routes?

Back 23

1. Routes must be a successor or feasible succesor
2. FS successor routes where metric <= current FD * variance
3. maximum-paths allows more paths

Front 24

What is the purpose of EIGRP route filtering?

Back 24

1. Prevent some (perhaps branch office or stub) routers from routing packets from one part to the network to another.
2. Reduce size of routing tables

Front 25

What are the IOS commands and mode for three different ways of implementing EIGRP route filtering?

Back 25

router configuration mode.
1. #distribute-list <acl> { in | out } [interface]
2. #distribute-list prefix <name> { in | out }
3. #distribute-list route-map <name> { in | out }
Note: for the ACL option, if interface is not supplied, the list applies to the router.

Front 26

What components of an IP route can be mached by a prefix-list?

Back 26

1. The route prefix (subnet)
2. The prefix length (mask)

Front 27

What is the command to create a prefix list?

Back 27

#ip prefix-list <name> [seq <number>]
{deny | permit <prefix>/<len>}
[ge <n>] [le <n>]

Front 28

What must be true for a prefix list to match a route?

Back 28

1. route's prefix must be in range implied by list's prefix/length
2. route's prefix length must fall within list's range

Front 29

What are the four rules for matching the prefix-length of a prefix-list?

Back 29

1. if neither ge or le, then conf-len = route-len
2. if both ge and le, then ge <= route-len <= le
3. if only le, then conf-len <= rout-len <= le
4. if only ge, then ge <= route-len <= 32

Front 30

What is the syntax of a route-map?

Back 30

#route-map <name> { permit | deny } [<seq-num>].
#match <criteria>

Front 31

What is the default result of a route-map if none of the criteria match? How do you change the default behavior?

Back 31

1. implied deny at end
2. Add a permit statement at end with no match criteria

Front 32

What does a route-map do when a permit condition is matched?

Back 32

Route is allowed through

Front 33

What does a route-map do when a deny condition is matched?

Back 33

Route is filtered

Front 34

What does a route-map do when it uses an ACL or prefix-list for matching?

Back 34

If the result is "permit", the match is successful.
If the result is "deny", the match is unsuccessful and it passes to the next statement.

Front 35

How do you verify a route-map?

Back 35

#show route-map <name>

Front 36

On which routers does EIGRP allow route summarization? How is this different than OSPF?

Back 36

EIGRP allows summarization at any router.
OSPF, allows summarization only at area border routers and autonomous system border routers.

Front 37

What are four benefits of route summarization?

Back 37

1. smaller routing tables
2. Reduces query scope
3. Summarization supported at any point in network (EIGRP)
4. Summary has metric of the best of the subnets being sumarized

Front 38

What are two tradeoffs of route summarization?

Back 38

1. May cause suboptimal routing
2. Packets destined for inaccessible destinations will flow to the summarizing router before being dropped.

Front 39

What is the mode and command to configure EIGRP route summarization?

Back 39

config-interface mode
#ip summary-address eigrp <asn> <prefix> <subnet-mask>

Front 40

When an EIGRP summary route is configured on an interface, what 4 steps does the router take?

Back 40

1. Brings down and back up all neighbor relationships on that interface, thus flushing topology data.
2. Advertises a summary route, assuming the router has at least one route in the summary range.
3. Does not advertise the subordinate (summarized) routes
4. Adds a route to its own routing table for the summary prefix/length with outgoing interface null0