Category: Route

iBGP – eBGP

 

eBGPiBGP
External BGPInternal BGP
NeighborBetween differnet ASWithin the same AS
Route updatesRoutes are send to eBGP peers by defaultRoutes are not send to BGP peers by default
AS path additionyesno
Administrative distance20200
TopologyDoes not require a full meshFull mesh or Route reflectors or Confedoration
Loop Preventionas-pathBGP split horizon

(more…)

BGP

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

(more…)

Policy Based Routing

  • 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

(more…)

IP SLA

  • 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

(more…)

Route Redistribution and Loops

  • 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

(more…)

OSPF Stub Areas

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.

(more…)

OSPF Default Routing

  • 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.

(more…)

OSPF Route Filtering and Summarization

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

    (more…)

OSPF Metric Calculations & Tuning

    • 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.

(more…)