Term
| who will a router send LSAs to? |
|
Definition
| "ADJACENT" routers only. These routers will then repackage and forward to their adjacent neighbors where necessary. |
|
|
Term
| what will a router do when it receives and LSA? |
|
Definition
| store a copy in the database and forward a copy to adjacent neighbors. |
|
|
Term
| ospf link-state refresh (paranoid) timer |
|
Definition
|
|
Term
| how is the router-id chosen. |
|
Definition
1. manual config
2. highest active loopback
3. highest active ip address |
|
|
Term
| what happens if the router-id is taken from a physical interface, and that interface fails? |
|
Definition
| the router continues to use that router-id until the process is restarted. |
|
|
Term
|
Definition
10 secs - broadcast, p2p
30 secs - NBMA, p2mp |
|
|
Term
|
Definition
|
|
Term
| info contained in hello packet |
|
Definition
Router ID of the originating router.
Area ID of the originating router interface.
Address mask of the originating interface.
Authentication type and authentication information for the originating interface.
HelloInterval of the originating interface.
RouterDeadInterval of the originating interface.
Router Priority.
DR and BDR.
Flags
Router IDs of the originating router’s neighbors. |
|
|
Term
| what values of a hello packet must match, for a neighbor relationship to be established? |
|
Definition
area
authentication
network mask
hello interval
dead interval
mtu
options |
|
|
Term
| what values of a hello packet must be unique, for a neighbor relationship to be established? |
|
Definition
interface ip address
router id |
|
|
Term
| a router receives a hello, which has its own router id listed as one of the neighbors on the link. What does this signify? |
|
Definition
| 2-way communication has been established. |
|
|
Term
| list the 5 ospf network types. |
|
Definition
Point-to-point networks
Broadcast networks
Nonbroadcast Multiaccess (NBMA) networks
Point-to-multipoint networks
Virtual links |
|
|
Term
| ospf multicast addresses for hello packets |
|
Definition
224.0.0.5 - all spf routers
224.0.0.6 - all DR/BDR |
|
|
Term
| what packets types are multicast to 224.0.0.6? |
|
Definition
|
|
Term
| default priority of an ospf multi-access interface. |
|
Definition
|
|
Term
|
Definition
it is used to hold the DR election when an interface is activated.
Equal to dead interval. |
|
|
Term
|
Definition
1. highest priority.
2. highest router-id. |
|
|
Term
| when an interface is activated, what happens if the router detects an active DR & BDR? |
|
Definition
|
|
Term
| what happens if there are no routers eligible for DR/BDR on a segment. |
|
Definition
no adjacencies will form.
All neighbor relationships will remain 2-way. |
|
|
Term
| components of an ospf interface |
|
Definition
IP Address and Mask
Area ID
Process ID
Router ID
Network Type
Cost
transmit delay
state
priority
DR
BDR
Hello interval
dead interval
wait timer
retransmit interval (default 5 secs)
hello timer
neighboring routers (adjacencies)
authentication type
authentication key |
|
|
Term
| how is cost calculated and how can this calculation be amended? |
|
Definition
100Mbps/BW
auto-cost reference-bandwidth |
|
|
Term
|
Definition
Down
Point-to-Point
Waiting
DR
Backup
DRother
Loopback |
|
|
Term
|
Definition
|
|
Term
| describe the poll interval |
|
Definition
| used for neighbors on nbma networks. Hello will be sent every poll interval if neighbor is down. |
|
|
Term
| components of neighbor data structure that are displayed in "sh ip ospf nei" |
|
Definition
Neighbor ID
Neighbor IP Address
Area ID
Interface
Neighbor Priority
State
Designated Router
Backup Designated Router
PollInterval
Neighbor Options
Inactivity Timer |
|
|
Term
|
Definition
down
attempt
init
2-way
exstart
exchange
loading
full |
|
|
Term
| describe the down neighbor state |
|
Definition
no hellos heard in last dead interval.
Hellos not sent unless network is nbma. |
|
|
Term
| describe the attempt neighbor state |
|
Definition
only for nbma networks.
Neighbor is transitioned to attempt when interface becomes active. |
|
|
Term
| describe the init neighbor state |
|
Definition
hello seen in last dead interval.
RIDs of neighbors included in hello. |
|
|
Term
| describe the 2-way neighbor state |
|
Definition
router has seen its own RID in received hello.
Bidirectional comms established. |
|
|
Term
| describe the exstart neighbor state |
|
Definition
| master/slave determined by highest RID. |
|
|
Term
| describe the exchange neighbor state |
|
Definition
| DBD packets sent, LSRs may also be sent. |
|
|
Term
| describe the loading neighbor state |
|
Definition
| LSRs sent and answered with LSUs. |
|
|
Term
| describe the full neighbor state |
|
Definition
fully adjacent.
Adjacencies appear in Router and Network LSAs. |
|
|
Term
| 2 methods of acknowledging an LSA. |
|
Definition
explicit - LSAck
implicit - LSU containing same instance of LSA. |
|
|
Term
| describe the I, M and MS bits of a DBD Packet. |
|
Definition
I - Initial - the first DBD packet sent.
M - More - indicates there will be more DBD packets.
MS - Master/Slave - set by the master. All routers will assume they are the master initially. |
|
|
Term
| what packet types are used during flooding? |
|
Definition
|
|
Term
| what is the scope of an LSU and LSAck packet? |
|
Definition
| both travel between 2 adjacent nodes. |
|
|
Term
| what is the scope of an lsa? |
|
Definition
| LSAs will be flooded throughout the area, but they will be packaged in a new LSU every hop. |
|
|
Term
| how are updates sent on each interface type? |
|
Definition
p2p - multicast to 224.0.0.5
broadcast - multicast to 224.0.0.5/224.0.0.6
virtual link - unicast
p2mp - unicast
nbma - unicast |
|
|
Term
| how are LSU retransmissions sent? |
|
Definition
|
|
Term
|
Definition
delayed - unicast/multicast
direct - unicast |
|
|
Term
| when are direct LSAcks sent? |
|
Definition
1. when a duplicate LSA is received from a neighbor.
2. When the LSA is max-age and it doesn't exist in the receiving router's DB. |
|
|
Term
| which 3 values determine that an LSA is the most recent version and what is the command to view them all? |
|
Definition
seq number
checksum
age
sh ip ospf database |
|
|
Term
|
Definition
|
|
Term
| default transmit delay (inftransdelay) and command to change it. |
|
Definition
1 second
ip ospf transmit-delay |
|
|
Term
| what does a router do when it needs to flush an LSA from all databases? |
|
Definition
| It prematurely sets the maxage and refloods. |
|
|
Term
| who can prematurely maxage an lsa? |
|
Definition
| only the router that originated the lsa. |
|
|
Term
|
Definition
1. to link an isolated area to the backbone.
2. to restore a partitioned backbone. |
|
|
Term
|
Definition
1. must be configured on ABRs, 1 connects to area 0.
2. Transit area must have full routing info.
3. Transit area cannot be a stub area. |
|
|
Term
| what is the interface state of a virtual link? |
|
Definition
|
|
Term
| what problem does "lsa group pacing" solve? |
|
Definition
| it ensures efficient LSA refreshes by batching updates every 240 secs by default. This prevents a full database dump every 1800 secs. |
|
|
Term
| command to amend lsa group pacing. |
|
Definition
|
|
Term
|
Definition
1 - Router LSA
2 - Network LSA
3 - Network Summary LSA
4 - ASBR Summary LSA
5 - AS External LSA
6 - Group Membership LSA
7 - NSSA External LSA
8 - External Attributes LSA
9 - Opaque LSA (link-local scope)
10 - Opaque LSA (area-local scope)
11 - Opaque LSA (AS scope) |
|
|
Term
| who originates type 4 LSAs? |
|
Definition
|
|
Term
| which lsa types are not associated with a particular area? |
|
Definition
|
|
Term
| which lsa types are filtered from a stub area |
|
Definition
|
|
Term
| how is a stub area identified at packet level? |
|
Definition
| the E-bit will be set to zero in hello packets. |
|
|
Term
| describe the P-bit in a type 7 LSA header. |
|
Definition
when P=1, LSA7 will be translated to LSA5 on the ABR.
when P=0, LSA7 will not be translated to LSA5 on the ABR. |
|
|
Term
| if an asbr advertises an external route into both a regular area and an nssa area, what will be special about the type7 lsa? |
|
Definition
| the P-bit will be set to 0, meaning the ABR will not translate to lsa5. |
|
|
Term
| what is the order of preference for ospf path types? |
|
Definition
| intra > inter > E1/N1 > E2/N2 |
|
|
Term
| maximum number of equal cost paths and command to limit between 1-6. |
|
Definition
|
|
Term
| what happens to LSAs, at packet level, as they are sent over a demand circuit? |
|
Definition
DNA bit is set.
Demand Circuit bit (DC) is added to advertise demand circuit capability. |
|
|
Term
| what is filtered over a demand circuit? |
|
Definition
hello packets (not on broadcast links).
Link state refresh. |
|
|
Term
|
Definition
Hello - 1
DBD - 2
LSR - 3
LSU - 4
LSAck - 5 |
|
|
Term
|
Definition
0 - null
1 - clear text
2 - cryptographic |
|
|
Term
|
Definition
| LSA headers for all known LSAs. |
|
|
Term
| what L3/L4 headers will an LSUpdate packet contain? |
|
Definition
IP header
OSPF header
LSU header
LSA headers |
|
|
Term
| identify the DN, O, DC, N, P and E option bits. |
|
Definition
DN - prevents looping when ospf is transported in MBGP.
O - indicates support for opaque LSAs.
DC - support for demand circuits.
N - support for LSA7.
P - Indicates that LSA7 should be translated to LSA5
E - External LSA support AKA stub flag |
|
|
Term
| if forward address is non-zero for a type 5 lsa, why must the forward address exist in the routing table? |
|
Definition
| because the forward address references a route, not a router-ID (like the advertising-router). |
|
|
Term
| if the route to an external LSA's forward-address is known via another protocol, will the external LSA be valid? |
|
Definition
| No, because OSPF can't guarantee it is loop free. The forward-address must be an internal OSPF route. |
|
|
Term
| 4 methods to filter a forward-address for an external route, that was generated in an NSSA area. |
|
Definition
1. area range not-advertise
2. area filter-list
3. ip ospf prefix-suppression
4. area nssa translate type7 suppress-fa |
|
|
Term
| How is the forward address selected, when a type 7 is translated to a type 5? |
|
Definition
| It is the router-ID of the ASBR. |
|
|
Term
| Who sets the forward-address, the router performing the redistribution or the translator? |
|
Definition
| the router performing the redistribution. |
|
|
Term
| Is it possible for an N2 route to be preferred over an E2 route? |
|
Definition
Yes.
E2 > N2 only if the metrics (and forward metrics are equal). Otherwise preference is based on metric. The same applies to N1/E1. |
|
|
Term
| What is the recommended method of engineering multiple external routes? |
|
Definition
| use metric-type to distinguish. Type 1 always beats type 2. |
|
|
Term
| how are intra-area external and inter-area external routes handled? |
|
Definition
| intra-area external > inter-area external |
|
|
Term
| what should you do after adding authentication to a virtual link config? |
|
Definition
| restart the process or bounce the virtual-links. Virtual-links run as a demand circuit, so any issues may not be experienced until updates are generated. |
|
|
Term
| how is the metric of a virtual-link determined and what issue might this cause? |
|
Definition
the metric is equal to the metric between the two endpoints.
As the virtual-link is an interface, it has a max cost of 65536. The metric between the two endpoints may exceed this value, if it does, the virtual-link will not form. |
|
|
Term
| what LSA types can an ABR summarise using the "area range" command? |
|
Definition
LSA 1 & LSA2
LSA 3 from other areas can't be summarised. |
|
|
Term
| where must external prefixes be summarised |
|
Definition
| either at the point of redistribution or on the LSA7/5 translator. |
|
|
Term
| what if multiple network commands match an interface on a router, in what order are they processed? |
|
Definition
| Network commands are processed sequentially, beware of overlapping commands that reference different areas. |
|
|
Term
| when can tags be applied to ospf routes? |
|
Definition
| at the point of redistribution only. |
|
|
Term
| 4 inter-area filtering methods. |
|
Definition
1. area range not-advertise.
2. area filter-list
3. summary-add not-advertise (NSSA ABR)
4. prefix-suppression |
|
|
Term
| 3 interface types that are not suppressed by the "prefix-suppression" command. |
|
Definition
1. loopback
2. secondary
3. passive-interfaces |
|
|
Term
| 3 methods to perform RIB filtering in OSPF. |
|
Definition
1. distribute-list with ACL.
2. distribute-list with route-map.
3. AD filtering. |
|
|
Term
| command to generate a stub router advertisement. |
|
Definition
|
|
Term
| command to minimise the number of redistributed routes in the database. |
|
Definition
redistribute maximum prefix 1200 80
will generate a warning when the 80% threshold is reached. |
|
|
Term
| command to limit the amount of LSAs in the database. |
|
Definition
|
|
