Category: Route

• Local router find the outgoing interface for the neighbor
• the IP of the outgoing interface is used as the source IP by default.
• With one link a failure in that link can lose the neighborship.
  •  configure two neighbor commands
  • Use the loopback interfaces as TCP endpoints
• Loopback links between two AS might miss the route to the peer’s loopback
  • fixed with multihop (TTL=255 instead of TTL=1).
    
    • create routes between peers to reach loopback address.
    • configure update-source so the right source-ip is used.

R10#(config)router bgp 10
R10#(config-router)neighbor 20.20.20.20 remote-as 20
R10#(config-router)neighbor 20.20.20.20 ebgp-multihop
R10#(config-router)neighbor 20.20.20.20 update-source loopback0

R20#(config)router bgp 20
R20#(config-router)neighbor 10.10.10.10 remote-as 10
R20#(config-router)neighbor 10.10.10.10 ebgp-multihop
R20#(config-router)neighbor 10.10.10.10 update-source loopback0

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• eBGP ad  20
• iBGP  ad 200
• BGP uses TCP port 179
• Designed as an Exterior gateway Protocol.

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• PBR intercepts packets before regular routing
• PBR overwrites the router’s natural destination
• PBR is tied to route-maps
  • Define the match criteria
  • Define the action for the packets
•  Packet forwarding
  • Outgoing interface
  • IP Next-Hop

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• Can be used by various
  • PBR
  • Static route
  • HSRP
• Feature to monitor destination
  • Cpu creates data to monitor
  • Operations
    • ICMP, RTP, TCP, UDP, DNS, DHCP, HTTP, FTP
  • Different operations can be monitored at the same time
• The receiver can be a router or host
  • Might be configured as a SLA Responder

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• One link within each routing domain
• Working routing config for each routing domain
• Redistribution configuration between routing protocols
  • Mutual redistribution
  • Bi-directional redistribution

Redistribution into EIGRP

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There are four types of stub areas

• stub
• totally-stubby
• not-so-stubby areas (NSSA)
• totally not-so-stubby areas
• All stub areas do not allow Type 5 (external) LSAs (ABR always filters them)
• For the totally stub areas the ABR filters the Type 3 LSAs.

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• Create a default route into a specific area
• Create a default route into the entire OSPF domain
• Default-information originate
  • Creates a default route into OSPF, external Type 2 route, using a Type 5 LSA with metric 20
  • default-information originate (always) metric 30 metric-type 1 route-map NAME
    
    • Default metric 20
    • Default metric-type 2
      • metric-type 1 cost can be changed
        
      • metric-type 2 cost can’t be changed
  • The metric-type defines LSA is Type 1 External or Type 2 External (default)
  • Route-map is used for tracking networks. If Route-map condition is met, default route is advertized.

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OSPF Route filtering between areas

• Filtering prevents the creation of LSAs.
• LSDB’s have to be the same for all routers ifnot SPF logic will fail
• OSPF can filter the originiation of LSA between areas
• Type 3 LSAs are filtered prior to origination ABR
  • • With multiple ABRs filtering should be done on both.
    • ospf# area number prefix-list prefix name in|out
      • In: IOS filters routes comming in to that area
      • out: IOS filters routes comming out of that area

  ip prefix-list NAME seq 5 deny 10.10.10.0/24 le 32
  ip prefix-list NAME seq 10 permit 0.0.0.0/0 le 32
  
  R1#(config-router)#area 1 filter-list prefix NAME in
  R1#show ip ospf database summary self-originate

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• • Analyse the LSDB to find all possible routes to reach the subnet.
  • Per route, add the interface cost for all outgoing interfaces in that route.
  • Pick the route with the lowest cost.
    • Cost is derived from the egress interface bandwith.

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