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Cisco SPRI 300-510 study materials
Cisco SPRI 300-510 study resources

Cisco SPRI 300-510: Routing Protocol Implementation and Optimization (OSPF, IS-IS, and Route Redistribution)

Cisco SPRI 300-510 · Work through your exam, one topic at a time.

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Routing Protocol Implementation and Optimization (OSPF, IS-IS, and Route Redistribution)

What this domain tests

The Routing Protocol Implementation and Optimization domain checks whether you can run OSPFv2/v3 and IS-IS in a service-provider IGP core and move prefixes between them without loops or suboptimal paths. Expect LSA/LSP-level troubleshooting, area and level design, and redistribution policy built from route-maps, tags, and seed metrics.

OSPF essentials

  • LSA types: 1 router, 2 network, 3 summary, 4 ASBR summary, 5 external, 7 NSSA. Stub areas block type 5; totally stubby areas also block type 3; NSSAs block type 5 but allow type 7.
  • An NSSA ABR translates type 7 to type 5 when the P-bit is set and the forwarding address is reachable.
  • Virtual links must cross a normal transit area, not a stub or NSSA, and must terminate on an ABR.

IS-IS essentials

  • A NET is area ID + 6-byte system ID + NSEL 00. L1 is intra-area; L2 is the backbone. An L1/L2 router sets the attached bit so L1 routers can install a default toward L2.
  • On broadcast links the DIS is chosen by priority, then highest MAC; there is no backup DIS. CSNPs and PSNPs keep databases synchronized.
  • Narrow metrics max at 63; wide metrics support TE and tags. Every router in the level must use the same metric style.

Redistribution rules

  • OSPF seeds redistributed routes with metric 20 by default; set default-metric or a per-statement metric.
  • subnets is required when redistributing classless prefixes into OSPF.
  • Tag routes at the first ASBR and deny that tag at the second ASBR to break mutual-redistribution feedback loops.
  • OSPF external type 1 adds the external cost to the internal cost; type 2 does not.

Worked example

An ASBR runs OSPF process 1 and IS-IS. IS-IS routes must enter OSPF as E1 with metric 50, OSPF routes must enter IS-IS with metric 100, and IS-IS-origin routes must not feed back.

route-map ISIS-TO-OSPF permit 10
 set tag 100
 set metric 50
 set metric-type type-1
route-map OSPF-TO-ISIS deny 10
 match tag 100
route-map OSPF-TO-ISIS permit 20
 set metric 100
router ospf 1
 redistribute isis metric 50 metric-type 1 subnets route-map ISIS-TO-OSPF
router isis
 redistribute ospf 1 metric 100 route-map OSPF-TO-ISIS

The tag is carried on the IS-IS routes that enter OSPF, so the OSPF-to-IS-IS route-map drops them instead of sending them back. E1 makes the metric additive, preventing a remote ASBR from attracting traffic with a lower E2 cost.

Traps

  • A virtual link through a stub or NSSA area fails.
  • NSSA type 7 without a reachable forwarding address is not translated.
  • IS-IS metric-style mismatch breaks route calculation.
  • Redistribution without subnets loses host prefixes.
  • OSPF E2 cost is not added to the internal cost, which can select a suboptimal exit.