Bogović small corner

Hero

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ospf

 
  • Feb 01, 2021

do not increment metric and start with 200

conf t
router ospf 1
redistribute static subnets metric 200 metric-type 2

when changing router-id

conf t
clear ip ospf process

loopback to “normal” interface

conf t
int lo 1
ip ospf network point-to-point

check DR and BDR

show ip ospf neighbour
show ip ospf interface

force DR on R1

interface FastEthernet0/0
 ip address 172.30.0.1 255.255.255.0
 ip ospf priority 200
 duplex auto
 speed auto
!
--> and set prio on others to 0

change hello interval for p2x interfaces

same hello on all routers

conf t
router ospf 1
ip ospf hello-interval 10

little troubleshooting

  • name must be uniqe
  • broadcast 10 sec hello message
  • NBMA 30 sec hello message

ospf interface config

conf t
  router ospf 1
  interface gig0/1
  ip ospf 1 area 0

cost change

correcting-cost

# R1-R4 (area 0)
conf t
  router ospf 1
  net 10.0.0.0 0.0.255.255 area 0
end

# R3-R5-R7 (area 1)
conf t
  router ospf 1
  net 10.1.0.0 0.0.255.255 area 1
end

# R4-R6-R8 (area 2)
conf t
  router ospf 1
  net 10.2.0.0 0.0.255.255 area 2
end

# To fix the reference bandwidth (all routers)
conf t 
  router ospf 1
  auto-cost reference bandwidth 1000

interface-cost

reduce type 5 and 4 LSAS messages with “STUB”

router ospf 1
  redistribute static subnets metric-type 1 metric 3
  • R4, R6, R8 - turn into STUB 
    conf t
router ospf 1
area 2 stub

reducing LSAS 3, 4 and 5

  • R7 
    conf t
router ospf 1
redistribute static subnets
end
  • R6, R8 
    conf t
router ospf 1
area 2 stub
end
  • R4 <– LSA 3, 4, 5 
    conf t
router ospf 1
area 2 stub no-summary
end

priority and router ID

  • R1, R2 
    conf t
int gig0/1
ip ospf priority 6
end

administrative distance and interface cost

  • R4 
    conf t
router ospf 1
distance 77
# for R3 to mark the routes
distance 33 3.3.3.3 0.0.0.0 
end
  • R2 
    conf t
int gig0/2
ip ospf cost 3
end

authentication

  • R1, R2 
    conf t
router ospf 1
area 0 authentication message-digest
# interface level
int g0/2
ip ospf authentication message-digest
ip ospf message-digest-key 1 md5 somereallystrongpassword
end

conf t
  router ospf 1
  default-information originate always
  # to advertise no matter if the default route exist
end

summarize ABR

  • R3, R4 
    conf t
router ospf 1
# R4
  area 0 range 10.0.0.0 255.255.0.0
  area 2 range 10.2.0.0 255.255.0.0
# R3
  area 0 range 10.0.0.0 255.255.0.0
  area 1 range 10.1.0.0 255.255.0.0
end

filtering routes ABR

  • R4 
    conf t
router ospf 1
area 0 range 10.0.0.0 255.255.0.0 not-advertise
end

filter with preefix list

  • R3 
    conf t
ip prefix-list no35  deny 10.1.35.0/24
ip prefix-list no35 permit 0.0.0.0/0 le 32
exit
router ospf 1
  area 0 filter-list prefix no35 in
  end

local OSPF route filtering

  • R2 
    conf t
access-list 10 deny 10.1.35.0
access-list 10 permit any
router ospf 1
destribute-list 10 in
end

filtering at the ASBR

  • R1
conf t
  access-list 1 permit 10.11.11.16
  route-map no16 deny 10
    match ip address 1
    exit
  
  route-map no26 permit 20
    set metric-type type-1
    set metric 6789
    end
  
  router ospf 1
    redistribute static subnets
    end

LSA Types

LSA

NSSA - Type 7

  • R4, R6, R8 
    conf t
router ospf 1
  area 2 nssa
  end
  • R7 
    conf t
router ospf 1
  redistribute static subnets
  end
  • R8 
    conf t
 router ospf 1
  redistribute static subnets
  end
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