Thursday, July 21, 2011

Route Redistribution & Metrics in EIGRP-OSPF with ASBR & ABR Routers

Here is one more topology I busted, Route Redistribution in EIGRP-OSPF with routers playing different ASBR/ABR roles. This involves 10 Router configurations. Basically, In Route redistribution we are allowing one routing process to distribute his own routes into another routing process with different metrics & parameters. This also includes Route-Mapping which I will cover in another topology. So if a router has EIGRP & OSPF procotol running, then "redistribute ospf <<process id>>" statement in EIGRP router plane will allow the OSPF routes to be distributed into respective EIGRP zone. However you have to take care of metrics & AD phenomena at the time of redistribution. Both protocols follow different type of metric sets. Auto-Summary is needed by EIGRP in this topology.



Notes - 
  • Router R3 & R10 are connecting OSPF & EIGRP protocols. Think of this like two Companies have a merger with one running EIGRP & Other OSPF in backbone.
  • R5 & R6 are in OSPF area 0 with R5 as ABR.
  • Routes are redistributed into each of the Router planes.
  • Routers in EIGRP region sees all external routes as EIGRP  External. "sh ip route" shows it as D EX flag.
  • Routers in OSPF region sees all external EIGRP routes as OSPF external 2 routes. "sh ip route" shows it as O E2 flag.
  • Routers in OSPF region sees all external OSPF routes as OSPF Inter-area. "sh ip route" shows it as O IA Flag
  • Redistributed Routes into OSPF are E2 type by default. Remember complete end to end cost is not reflected when route is detected as E2. E1 i.e. External Type 1 reflects total end to end cost of the route. This can be done using "metric-type 1" at the time of redistribution of protocols into OSPF routing process. Here Routes E2 type.
  • R10 connects EIGRP AS130 with OSPF Area 20. Redistribution of OSPF Area 20 routes into  EIGRP AS 130 follows different metrics. EIGRP protocol works with K values so at the time of redistribution of routes following metrics are required
      • Bandwidth
      • Delay in milliseconds
      • Reliability
      • Line Load
      • MTU
  • I have used standard metrics for Redistributing OSPF routes into EIGRP "56000 10 255 255 1500" in all routers except for R10 Router. Keeping same metrics while redistributing EIGRP AS120 into EIGRP AS130 & redistributing OSPF Area 20 into EIGRP AS130 causes routing black-hole. R12 finds two paths to go for the desired network with equal cost. Hence to avoid this while redistributing OSPF into EIGRP at R10 metrics used are "56000 12 255 255 1500". Notice the Delay value present 12 ms delay result in EIGRP choosing low delay 10 ms link over this route. Hence R12 chooses 61.1.1.2 interface to route to external networks. 102.1.1.2 is only chosen in case of very near networks in OSPF Area 20 region.
  • If 61.1.1.0 network goes down then 102.1.1.0 network will be used for all the routing.
  • Cloud interfaces bridged with Oracle Virtual Box Interfaces are connected to Microcore Linux to verify the network. SW2 with VLAN 4 & 2 connected to Microcore.
All the Router configurations can be downloaded from here


Happy Networking!

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