Matt Cisco 1

Front 1

What is CEF

Back 1

Cisco Express Forwarding.

1) Starts CEF Switching
2) Creates FIB Tables

Front 2

What does the ip cef [distributed] command do?

Back 2

Enables CEF down to all interfaces capable of CEF.

Usually a default enable on new, needed on 7100, 7200, 7500

Front 3

What are the steps required to configure MPLS?

Back 3

1) Enable CEF to create FIB table
2) Configure MPLS to start LDP
3) Configure MPLS LDP protocol

Front 4

What is the FIB, LFIB, and difference between them?

Back 4

FIB: Routing table for unlabeled packets, formed by routing protocols (OSPF, BGP)

LFIB: Label table for labeled packets, formed by LDP protcols

Front 5

What are the MPLS tag protocols?

Back 5

LDP and TDP. tdp is 3rd party.
you can enable both on an interface

Front 6

How do service providers typically prevent customers from sending their own LDP tags?

Back 6

Usually via ACL blocking port 646 on customer side interface

Front 7

What are the possible label operations in MPLS?

Back 7

1 - Swap
2 - Push (apply)
3 - Pop (remove)

Front 8

What is the Penultimate Hop Popping (PHP)?

Back 8

Second to last LSR in an LSP which removes label so only IP lookup is done on last LSR.

Should also be the last multi-connected LSR in network. Typically a "P" router, whereas "PE" router is IP lookup in LFIB

Front 9

What are the steps to configure and verify MPLS LDP?

Back 9

1) enable
2) Config t
3) mpls ip
4) mpls label protocol ldp
5) interface s0/0.1
6) mpls ip
7) exit
8) exit
9) sh ip mpls int
10) sh ip mpls ldp discovery [all | vrf)
11) sh ip mpls ldp neighbor

Front 10

What are the steps to configure and verify MPLS LDP not directly connected networks?

Back 10

enable
confi t
mpls ip
mpls label protcol ldp
interface tunnel10
tunnel-destination 10.10.10.10
mpls ip
exit
exit
sh mpls ldp discovery
one side can be "mpls ldp discovery targeted-hello accept"

Front 11

When would you configure an interface using both LDP and TDP?

Back 11

When that equipment or interface connects to networks and devices which only support tdp. tdp not common but fully compatible and shows in the FIB fine

Front 12

What MTU sizes should be used with various MPLS flavors?

Back 12

Normal LAN MTU is 1500
Pure MPLS increases MTU to 1504
MPLS VPN requires 2 label increase to 1508
MPLS VPN-TE requires 3 label increase to 1512

Interface MTU increase on WAN interfaces is automatic
Interface MTU increase on LAN interfaces is NOT

Front 13

How could MTU affect routing protocols?

Back 13

Particularly in OSPF, "hello" parameters include an MTU size, if this is hard coded and doesn't match, adjacencies will never form

Front 14

What are the steps to configure and verify MPLS VPN?

Back 14

ip cef
ip vrf sample_A
rd 100:110
route-target export 100:1000
route-target import 100:1000

interface loopback0
ip address 10.10.10.4 255.255.255.255
ip router isis

interface loopback101
ip vrf forwarding sample_A
ip address 200.0.4.1 255.255.255.0

router bgp 100
bgp log-neighbor-changes

neighbor 10.10.10.6 remote-as 100

neighbor 10.10.10.6 update-source loopback0

address-family vpnv4
neighbor 10.10.10.6 activate
neighbor 10.10.10.6 send-community both
exit-address-family

address-family ipv4 vrf sample_A
redistribute connected
no auto-summary
no synchronization
exit-address-family

Front 15

What are the two primary issues when dealing with generic protocol re-distribution?

Back 15

1) Sub-optimal routing
2) Routing loops
3) Slow convergence

Front 16

Rules of thumb on protocol re-distribution

Back 16

Redistribution rules of thumb

1) router should always prefer internal pre-fix information over external prefix information
2) router should never inject learned routes into the domain from which they were learned

Just remember that when routes are re-distributed, the metric must be understandable to the receiving protocol

Front 17

Configure basic IGRP/EIGRP redistribution

Back 17

IGRP/EIGRP re-distribution config
router igrp/eigrp 1
network 131.108.0.0
redistribute static
redistribute ospf 1
redistribute rip
redistribute isis
default−metric 10000 100 255 1 1500

Front 18

Configure basic OSPF redistribution

Back 18

OSPF re-distribution config
router ospf 1
network 131.108.0.0 0.0.255.255 area 0
redistribute static metric 200 subnets
redistribute rip metric 200 subnets
redistribute igrp 1 metric 100 subnets
redistribute eigrp 1 metric 100 subnets
redistribute isis metric 10 subnets

Front 19

Configure basic RIP redistribution

Back 19

RIP re-distribution config - always a low metric or routes will never be reached
router rip
network 131.108.0.0
redistribute static
redistribute igrp 1
redistribute eigrp 1
redistribute ospf 1
redistribute isis
default−metric 1

Front 20

Name some common solutions for filtering/altering redistribution metrics

Back 20

distribute-list
route-map
tag matching
tag setting
set metrics under redistribute command

Front 21

Name 3 uses for Local Policy Routing

Back 21

1) Re-circulate local-bound traffic
2) Traffic Filtering
3) To apply flow precedence, priority, packet size, etc

*12.3 added direct command to apply policy to
local generated traffic

Front 22

What LSA Types are impacted by the command clear ip ospf redistribution and where should you run this command?

Back 22

This command flushes the Type 5 and Type 7 LSAs. It would be run on the ASBR.

Front 23

What is the purpose of the LSA Type 8 in OSPF for IPv6?

Back 23

Link LSAs provide the link-local address of the router to all other routers attached to the link, inform other routers attached to the link of a list of IPv6 prefixes to associate with the link, and allow the router to assert a collection of Options bits to associate with the network LSA that will be originated for the link.

Front 24

What IEEE 802.1x keyword is used to with the dot1x port-control interface configuration command in order to enable IEEE 802.1x authentication and cause the port to begin in the unauthorized state, allowing only EAPOL frames to be sent and received through the port?

Back 24

Auto

Front 25

What is the stratum in NTP?

Back 25

NTP uses the concept of a “stratum” to describe how many NTP “hops” away a machine is from an authoritative time source.

Front 26

Some examples of advanced extended access-lists (BGP filtering can use instead of prefix lists)

Back 26

access-list <ACL #> permit ip <network> <wildcard mask of network> <subnet mask> <wildcard mask of subnet mask>

The source portion of the extended ACL is used to match the network portion of the BGP route and the destination portion of the ACL is used to match the subnet mask of the BGP route. Here are some examples:

access-list 100 permit ip 10.0.0.0 0.0.0.0 255.255.0.0 0.0.0.0
Matches 10.0.0.0/16 – Only

access-list 100 permit ip 10.0.0.0 0.0.0.0 255.255.255.0 0.0.0.0
Matches 10.0.0.0/24 – Only

access-list 100 permit ip 10.1.1.0 0.0.0.0 255.255.255.0 0.0.0.0
Matches 10.1.1.0/24 – Only

access-list 100 permit ip 10.0.0.0 0.0.255.0 255.255.255.0 0.0.0.0
Matches 10.0.X.0/24 – Any number in the 3rd octet of the network with a /24 subnet mask.

access-list 100 permit ip 10.0.0.0 0.255.255.0 255.255.255.0 0.0.0.0
Matches 10.X.X.0/24 – Any number in the 2nd & 3rd octet of the network with a /24 subnet mask.

access-list 100 permit ip 10.0.0.0 0.255.255.255 255.255.255.240 0.0.0.0
Matches 10.X.X.X/28 – Any number in the 2nd, 3rd & 4th octet of the network with a /28 subnet mask.

access-list 100 permit ip 10.0.0.0 0.255.255.255 255.255.255.0 0.0.0.255
Matches 10.X.X.X/24 to 10.X.X.X/32 – Any number in the 2nd, 3rd & 4th octet of the network with a /24 to /32 subnet mask.

access-list 100 permit ip 10.0.0.0 0.255.255.255 255.255.255.128 0.0.0.127
Matches 10.X.X.X/25 to 10.X.X.X/32 – Any number in the 2nd, 3rd & 4th octet of the network with a /25 to /32 subnet mask

Front 27

Steps to configure basic MPLS-TE using OSFP

Back 27

ip cef
mpls traffic-eng tunnels

interface loopback0
ip address 10.10.10.6 255.255.255.255

interface tunnel158
ip unnumbered loopback0
tunnel destination 10.10.10.4
tunnel model mpls traffic-eng
tunnel mpls traffic-eng autoroute announce
tunnel mpls traffic-eng priority 2 2
tunnel mpls traffic-eng bandwidth 158
tunnel mpls traffic-eng path-option 1 explicit name low

interface tunnel159
ip unnumbered loopback0
tunnel destination 10.10.10.4
tunnel model mpls traffic-eng
tunnel mpls traffic-eng autoroute announce
tunnel mpls traffic-eng priority 4 4
tunnel mpls traffic-eng bandwidth 159
tunnel mpls traffic-eng path-option 1 explicit name straight

tag-switching ip
mpls traffic-eng tunnels
frame-relay interface-dlci 603
ip rsvp bandwidth 512 512

router ospf 9
network 10.1.1.0 0.0.0.255 area 9
network 10.10.10.0 0.0.0.255 area 9
mpls traffic-eng area 9
mpls traffic-eng router-id loopback0

ip explicit-path name low enable
next-address 10.1.1.21
next-address 10.1.1.10
next-address 10.1.1.1
next-address 10.1.1.14

ip explicit-path name straight enable
next-address 10.1.1.21
next-address 10.1.1.5
next-address 10.1.1.14

end

Verify:
show ip ospf mpls traffic-eng link
show ip ospf database opaque-area

Front 28

Is MPLS a Layer 2 or Layer 3 Technology?

Back 28

It is considered both a L2 and L3 technology

Front 29

Does MPLS-TE functionality map to COS or QOS

Back 29

COS

Front 30

Name the common problems with MPLS?

Back 30

The Tag Distribution Protocol (TDP) or Label Distribution Protocol (LDP) session does not start.

The TDP or LDP session starts, but the labels are not allocated or distributed.
The labels are allocated and distributed, but the forwarded packets are not labeled.

The large IP packets are not propagated across the MPLS backbone, even though they were successfully propagated across the pure IP backbone.

Front 31

Common MPLS issues resolutions

Back 31

Check TDP and LDP eanbled and same on both sides

Ensure CEF is enabled

Enable MPLS globally as well as at interface level

Check label bindings and routes in FIB, LFIB, and LIB

MTU issues are common

Use MPLS-aware traceroute

Front 32

How do you use extended access-list to filter in a routing protocol?

Back 32

In short - Match the host to the subnet...
Extended IP access list 100
10 deny ip host 155.1.0.2 host 150.1.7.0

*NOT documented in command ref or doc-cd, must be remembered
This is goes back to being VERY SPECIFIC. Show everyone you
know exactly what you are doing

Front 33

What does EIGRP use the router-id field in external routes for?

Back 33

Loop prevention mechanism

if you want to prevent an external route from being installed, simply set it's router-id to the same as another router. Now neither router will originate external routes.

Front 34

What is EIGRP Feasibility Condition?

Back 34

Feasibility Condition is where a router could have a better metric than the Feasible Successor, but not be placed in the routing table due to having a longer Reported Distance.

The important note is that not all routes make it into the EIGRP routing table and should be viewed individually on routers

Front 35

List the 5 phases of OER (Optimized Edge Routing)?

Back 35

Profile Phase
Measure Phase
Apply Policy Phase
Control Phase
Verify Phase

Front 36

How can you resolve OSPF MTU issues?

Back 36

1) Change on LAN switches system mtu 1500, use sh sys mtu on 3560

2) Change MTU on router-interfaces (local, not WAN)

3) Issue the ip ospf mtu-ignore

Front 37

What is a Forwarding Equivalence Class (FEC)?

Back 37

FEC is a group of IP packets which are forwarded in the same manner, over the same path, and with the same forwarding treatment. An FEC might correspond to a destination IP subnet, but it also might correspond to any traffic class that the Edge−LSR considers significant. For example, all traffic with a certain value of IP precedence might constitute a FEC.

Front 38

What is RIB/FIB

Back 38

Routin Information Base(RIB) is the Table which is build up by Routing Protocols or static Routes. It could have the same entry for reaching one network with the corresponding metrics. The Forwarding Information Base(FIB) has only one entry per network, the FIB is gerated (as a subset) by the RIB, the FIB tuples are unique.

Front 39

What is LIB/LFIB

Back 39

The Label Forwarding Information Base (LFIB) is derived from the Label Information Base (LIB), it is a subset of the LIB. Also the LFIB contains no IP information whereas the LIB does hold IP information. Cisco says the LFIB is generated when the actual shortest path to a destination is chosen. Hence, in the LFIB there will be one label pair for a destination (or FEC), whereas the LIB holds all possible paths to the destination.

Front 40

What causes EIGRP FD to be inaccessible?

Back 40

The router is not using that EIGRP route in its routing table. Usually, the route is overridden by another routing protocol that has lower administrative distance

Front 41

What is the recommended way to send ony the default route out a given interface
in EIGRP?

Back 41

Use distribute -list to filter all outbound route advertisements sent out the interface with the
exception of the default (0.0.0.0)

NOTE: DO NOT use ip summary-address eigrp for this

Front 42

What is EIGRP route-leaking?

Back 42

Allowing a more specific and thus, preferred, route thorugh a summarization command

Front 43

How to configure EIGRP unequal cost load balancing.

Back 43

Variance

Front 44

When should you use the BGP "weight" attribute?

Back 44

NEVER!!

- Only local
- Causes Loops
- Defaults to higher, preferred value (32768 of 65535)

Front 45

How do you place routes into BGP?

Back 45

1) Network Statements
2) Protocol re-distribution

Front 46

True or False:

In the command sh ip bgp summ, a status of "active" means the bgp peer is actively advertising.

Back 46

FALSE!!

"active" means waiting in BGP speak

Front 47

List the common ways to filter BGP routes?

Back 47

Prefix-List, Route-Map, Filter-List

Front 48

What is the technical description, and differentiator, of a route-map?

Back 48

Cisco’s mechanism to select and modify routes with if/then style algorithms.

Route-maps are used for more than just BGP in a cisco router, such as traffic
shaping and policy routing.

Front 49

List the BGP decision algorithm selection order:

Back 49

- Do not consider IBGP patch if not synchronized
- Do not consider path if no route to next hop
- Highest weight
- Highest local preference
- prefer local route
- shortest AS path
- lowest origin code IGP<EGP
- lowest MED
- prefer EBGP over IBGP
- Path with shortest next-hop metric wins
- lowest router id

Front 50

What is a "Hold-Up" route?

Back 50

they are present only to make sure bgp advertises that network. the assumption, is that ure igp has more specific routes to all used subnets under that network. so, everyone is happy - bgp advertises your major network, and all routable destinations are routed by the igp once the packet reaches your AS

Front 51

Why should you cut/paste BGP neighbor configurations?

Back 51

1) Good policy and avoids errors
2) There is 1 30-45 second window after configuration of peer 1 before it starts to send and receive routes - whether your filters are present or not!
3) Can also configure session in "shut" state

Front 52

What are the steps to quick test your BGP advertisements?

Back 52

1) sh ip bgp
2) sh ip bgp neigh x.x.x.x adv
3) go to nitrous.digex.net or another looking glass and do a
route lookup to ensrue your routes are under your AS and
not your providers

Front 53

Name the most comon BGP attributes?

Back 53

Prefix, AS Path, Next-Hop, Weight, Local Pref, Origin Code, MED

Front 54

What process are community destinations usually applied with?

Back 54

Route-maps

Front 55

Follow these 4 steps when adding BGP routes:

Back 55

Use network statements to inject routes

Use AS-Path lists to control adv

Use AS Path padding to prefer-de-prefer externally heard routes

have full iBGP mesh

Front 56

You can clear BGP route tables with "clear ip bgp" and "clear ip bgp soft"

What;s the difference?

Back 56

Clear ip bgp blows away the table and causes massive relearn.

soft issues route withdrawls and recomputes

Front 57

What is the BGP TTL hack?

Back 57

Changing the expect TTL setting from default 255 to 254 or other non-common number

Front 58

What is DTP?

Back 58

Cisco proprietary (switch only) protocol) which auto negotiates VLAN trunking on an interface

Front 59

If one side of a trunk is configured as "desirable" what does that side do?

Back 59

Sends DTP frames, trunks if negotiation is successfull

Front 60

How do you configure a SVI?

Back 60

interface vlan[vlan#]

Front 61

In 802.1q encaps, each vlan is tagged with 4 byte tag. Which number is tagged for traffic sent and received on the "native" vlan?

Back 61

NONE!

Traffis sent and received on native vlan interface does not have tag inserted

Front 62

What vlan does control plane traffic transverse?

Back 62

VLAN 1

Front 63

What are the 5 default vlans?

Back 63

1 and 1002-1005

Front 64

If newly configured SVI interface shows down/down, what is probable cause?

Back 64

1) No ports on the new vlan
2) vlan must exist in vlan database

Front 65

Difference between PAGP and LACP

Back 65

PAGP usually L2 etherchannels
LACP usually L3 etherchannels

not compatible