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50 Cards in this Set
- Front
- Back
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What is the multicast address for all OSPF All-routers?
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224.0.0.5
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What is the multicast address for All-Designated routers?
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224.0.0.6
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Who is responsible for setting sequence numbers?
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The router with highest RID is designated master and is responsible for setting sequence numbers of the DD packets.
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What does DD packet contain?
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LSA headers and sequence numbers for each LSA (not full LSA's)
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In what case does a router request an LSR?
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When a router does not have an LSA described in a DD packet or has the LSA but with a lower sequence number
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What happens when a router receives an LSR?
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The router responds with a LSU (link state update) that contains a full copy of the LSA requested. Each LSR/LSU is acknowledged by sending back a duplicate LSR/LSU or by sending an LSAack packet.
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What happens when OSPF doesn't receive an ACK for it's LSR/LSU?
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The router will re-transmit the LSA to neighbours who have not sent an ACK. The frequency in which the LSA is retransmitted can be configured per interface:
'ip ospf retransmit-interval' |
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What is the default LSR-Refresh timer? What is the default LSA MaxAge timer?
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30 minutes and 60 minutes
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How do you disable LSA ageing process?
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ip ospf flood-reduction. Any LSA transmitted from this interface will be marked as Do Not Age, and therefore periodic LSA re-flooding is not necessary
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OSPF over FR:
Discuss 3 things about Non-Broadcast OSPF type in terms of DR/BDR election, hello intervals and whether it requires neighbour statement |
DR and BDR election
30 second hello intervals Requires neighbor statements (on DR). NBMA doesn't support broadcast, so you will need neighbor statements to send OSPF hello packets as unicast. |
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If you have non-broadcast configured in a partially meshed layer 2 topology, what is the next hop for the other spoke router?
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The next hop will be the other spoke router.
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OSPF over FR:
Discuss 3 things about Broadcast OSPF type in terms of DR/BDR election, hello intervals and whether it requires neighbour statement |
DR and BDR election
10 second hello internvals Doesn't require neighbour statement |
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In OSPF over FR, which network type required broadcast keyword in the FR config?
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Broadcast and Point-to-Multipoint since hello packets are sent as multicast, not unicast.
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OSPF over FR:
Discuss 3 things about Point-to-Multipoint OSPF type in terms of DR/BDR election, hello intervals and whether it requires neighbour statement |
No DR and BDR election
30 second hello intervals No neighbour statement required |
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Which two OSPF network types modifies the Next Hop values to the address of the connected neighbour when advertised across the NBMA cloud?
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P2MP and P2MP Broadcast.
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OSPF over FR:
Discuss 3 things about Point-to-Multipoint Broadcast OSPF type in terms of DR/BDR election, hello intervals and whether it requires neighbour statement |
No DR and BDR election
30 second hello intervals Requires neighbor statements (on DR) |
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OSPF over FR:
Discuss 3 things about Point-to-Point OSPF type in terms of DR/BDR election, hello intervals and whether it requires neighbour statement |
No DR and BDR election
10 second hello internvals No more than two hosts per subnet |
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Which LSA's do Stubby areas filter out?
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LSA 5
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Which LSA does Totally Stubby Areas filter out?
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LSA 3 and 5
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Which LSA does NSSA filter out? What is the benefit of having NSSA?
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LSA 5. It allows you to redistribute routes within NSSA, which you can't do with stubby and totally stubby areas.
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What LSA does Totally NSSA filter out?
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LSA 3 and 5. Allows redistributing routes within NSSA.
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Which area needs to be explicitly defined to a default route?
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NSSA (type 7 default route)
'area 1 nssa default-information originate' |
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Regardless of a route’s metric or administrative distance, OSPF will choose routes in a particular order: What is the order?
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Intra-Area (O)
Inter-Area (O IA) External Type 1 (E1) External Type 2 (E2) NSSA Type 1 (N1) NSSA Type 2 (N2) |
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What happens if multiple E2 routes exist with the same redistribution metric?
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The path with the lower forward metric (metric to the ASBR) is preferred.
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What does the command 'max-metric router-lsa on-starup XX' do?
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It makes the OSPF router set it's own Type-1 LSA to an infinite metric for XX amount of time after a reload.
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What does the command 'max-metric router-lsa on-startup wait-for-bgp do?
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It makes the OSPF router set it's own Type-1 LSA to an infinite metric until the BGP converges.
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What is the OSPF default metric when redistributing from an IGP
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20
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What is the OSPF default metric when redistributing from an BGP
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1
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What does the command 'max-metric router-lsa on-starup XX' do?
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It makes the OSPF router set it's own Type-1 LSA to an infinite metric for XX amount of time after a reload.
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What does the command 'max-metric router-lsa on-startup wait-for-bgp do?
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It makes the OSPF router set it's own Type-1 LSA to an infinite metric until the BGP converges.
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What is the OSPF default metric when redistributing from an IGP
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20
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What is the OSPF default metric when redistributing from an BGP
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1
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How do you summarise at the ABR?
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area x range y.y.y.y
The area x contains component subnets that will be summarised into y.y.y.y |
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How do you summarise at the ASBR?
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summary-address y.y.y.y
Only an ASBR can summarise external routes |
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What are the two methods used for route filtering in OSPF
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1. Preventing optimal paths generated by OSPF from entering the RIB (distribute-list in)
2. Affecting the LSA generation process |
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What is the configuration required to filter routers (not LSAs) if you want to deny 155.1.6.6 and permit everything else?
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router ospf 1
distribute-list 2 in Standard IP access list 2 10 deny 155.1.6.6 (4 matches) 20 permit any (5 matches) (denies 155.1.6.6 in entering the route table) |
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What are the 3 methods of filtering type 3 LSA's?
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Method 1: Filter the inter-area routes generated at ABR
Method 2: Filter out intra-area routes Method 3: Filter inter-area routes learned by ABR from Area 0 |
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What are the two ways of filtering routes (not LSA's) within an area
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1. Distribute-list in
2. Filtering with Admin Distance. |
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How would you filter inter-area routes to allow only 155.1.0.0/24 into area 1 from area 0?
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Method 1: Filter the inter-area route generated at ABR
area 1 filter-list prefix AREA1-FILTER-IN in ip prefix-list AREA1-FILTER-IN permit 155.1.0.0/24 (permits only summary LSA 155.1.0.0/24 and filters others) We are only allowing those routes matched by the prefix into area 1. Its from the perspective of the area not the router. Method 2: Filter intra-area route area 0 range 155.1.0.0 255.255.255.0 not-advertise (filters 155.1.0.0/24 going from area 0) Method 3: Filter inter-area routes learned by ABR router ospf 1 distribute-list 2 in Standard IP access list 2 10 deny 155.1.0.0 20 permit any |
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How do you filter LSA type 5 routes?
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Method 1:
router ospf summary-address 10.0.0.0 255.255.25.0 no advertise Method 2: router ospf redistribute rip route-map RIP_TO_OSPF Method 3 If the FA is 'non-zero' and not accessible, the corresponding external prefix is not installed into the global routing table |
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What conditions set the forwarding address field to a non-zero address?
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OSPF is enabled on the ASBR's next hop interface AND
ASBR's next hop interface is non-passive under OSPF AND ASBR's next hop interface is not point-to-point AND ASBR's next hop interface is not point-to-multipoint AND ASBR's next hop interface address falls under the network range specified in the router ospf command. Any other conditions besides these set the forwarding address to 0.0.0.0. |
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How do you filter LSA 7 routes?
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summary-address x.x.x.x y.y.y.y not-advertise
(The ABR becomes an ASBR and re-originates the routes, so this command can be used) Filter the forward-address IP from the routing table in the ABR using ' distribute-list in' and the LSA-5 won't be generated. |
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How do you reset the NSSA translated type-5 LSA to 0.0.0.0
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area X nssa suppress-fa
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How do you reset the NSSA translated type-5 LSA to 0.0.0.0
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area X nssa suppress-fa
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How do you inject a type-3 LSA default route with cost 30?
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area 1 nssa no-summary
area 1 default-cost 30 |
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How do you inject a type-7 LSA default route with cost 30?
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area 1 nssa default-information-originate
area 1 default-cost 30 |
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For a point-to-point OSPF link, which command is used to check the directly connected routers?
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show ip ospf database <local-ospf-id> self-originate
Link connected to: another Router (point-to-point) (Link ID) Neighboring Router ID: 150.1.1.1 (Link Data) Router Interface address: 155.1.0.5 Number of TOS metrics: 0 <snip> TOS 0 Metrics: 64 |
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For a broadcast OSPF link, which command is used to check the directly connected routers?
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within an area:
- show ip ospf database router x.x.x.x ->>>> cost to pseudo node (treats DR as a separate pseudo node) ->>>> x.x.x.x is local router-id Link connected to: a Transit Network (Link ID) Designated Router address: 155.1.108.10 (Link Data) Router Interface address: 155.1.108.10 Number of TOS metrics: 0 TOS 0 Metrics: 150 - show ip ospf database network 155.1.108.10 ->>>> shows attached devices |
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What are the two ways of totally filtering OSPF database?
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router ospf 1
neighbor 155.1.0.2 database-filter all out int vlan 79 ip ospf database-filter all out |
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How do you configure an interface to send OSPF hello packets every 250ms?
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ip ospf dead-interval minimal hello-multiplier 4
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