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 10.10.10.10 0.0.0.255
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 10.10.10.10 0.0.0.255
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