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

    • redistribute (protocol) (process-id, as-number) (metric) (match) (tag) (route-map)
    • Metric must be set for the routes
      • default-metric (thid prio)
      • metric bw  delay  reliability  load  mtu  on the redistribute command ( second prio)
      • route-map parameter on the redistribute command (first prio)
    • sh ip eigrp toplogy
      • output will show the routes as external routes.
access-list 1 permit
route-map CCNP permit 10
   match ip 1
   set metric 1000 100 255 1 1500
route-map CCNP permit 20
   set metric 10000 50 255 1 1500

router eigrp 10
   redistribute ospf 1 route-map CCNP

Redistribution into OSPF

show ip route
show ip database
show ip database external

  • OSPF has default metrics for redistributed routes (Default metric is 20).
  • OSPF also flags them as external.
  • When redistributed into OSPF;
    • Type 5 LSA
    • Type 7 LSA (into a NSSA).
  • Redistribute (protocol process id | as-number) (metric) (metric-type) (tag) (route-map) (subnets)
    • protocol (rip/ospf/eigrp/is-is etc)
    • process-id, as-number
    • metric defines a cost metric
    • metric-type 1|2  (Type 5 LSA | type 2)
    • tag
    • route-map
    • subnets Redistributes subnets of classless networks.  Without only classful networks are redistributed
  • Default metrics
    • taken from BGP: default metric 1
    • taken from OSPF: copy the route’s metric
    • other sources: Default metric is 20

Redistribution with Route-Maps

show ip access-list
show ip prefix-list
show ip route-map
show ip eigrp topology table
show ip ospf database
show ip rip database
show ip route

  • Identify subset of routes
  • Filtering choises
  • Different metrics values per route
    • set metric
    • Importing routes into rip/eigrp you can set a seed metric
access-list 1 permit
route-map CCNP permit 10
   match ip 1
   set tag 800
route-map CCNP permit 20

route-map CCNP-Match-Tag permit 10
   match tag 800
   match route-type external
route-map CCNP-Match-Tag permit 20
   match metric-type internel
   set metric-type type-1
   set metric 65
route-map CCNP-Match-Tag permit 30

router ospf 1
   redistribute eigrp 100 route-map CCNP-Match-Tag subnets
  • Different metric type for OSPF routes
  • Set route tags
  • Match command to match, rest is match everything

Multiple point of Redistribution

  • Avoids a single point of failure
  • Can create complexity issues
  • Can create a routing loop
    • Prevent routing loops with metric (hop count)
      • Change metric to a higher number than anything possible in the network.
    • Prevent routing loops with Administrative distrance
      • Rip
        • distance <value>
      • EIGRP
        • distance eigrp <internal-ad> <external-ad>
        • distance <value> <ip src> <wildcard mask>
      • OSPF
        • distance ospf <external ad> <intra-area ad> <inter-area ad>
        • distance <value> <ip src> <wildcard mask>
    • Prevent routing loops with Tags
      • set tag in a route map
      • tag persists through redistribution
      • redistribute connected route-map TAGGING

Path manipulation with redistribution

  • Changing metric values with redistribution
  • Changing metric type
  • Route filtering
  • Route summerization



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