I85PREP
⌘ K
JNCIE-SP study materials
JNCIE-SP study resources

JNCIE-SP: Interior Gateway Protocols and Routing Policy

JNCIE-SP · Work through your exam, one topic at a time.

All guide sections

Interior Gateway Protocols and Routing Policy

What this domain tests

IGP and policy questions test whether you can scale OSPF and IS-IS, redistribute safely, and predict policy evaluation. Expect route-filter syntax, policy default actions, OSPF external metrics, and IS-IS level and metric behavior.

Core rules

  • OSPF uses areas and LSA types 1/2 (intra-area), 3 (inter-area), 4/5 (ASBR/external), and 7 (NSSA). set protocols ospf area 0.0.0.0 interface ge-0/0/0.0 metric 20 sets interface cost; reference-bandwidth should be consistent across the area.
  • IS-IS uses L1/L2; set protocols isis level 2 wide-metrics-only is required for TE-style metrics. The overload bit (set protocols isis overload) makes the router a leaf for transit.
  • Routing policy is a list of terms evaluated top to bottom. Match with from protocol, from route-filter, from prefix-list, from community, or from as-path; act with accept, reject, next term, or next policy. If no term matches, the default action is reject.
  • route-filter modifiers matter: exact, longer, orlonger, upto /24, and prefix-length-range /25-/28.
  • OSPF redistribution requires an export policy. The action external type 1 makes the external cost add to internal cost; type 2 is the default and does not.

Worked example

Redistribute only static 203.0.113.0/24 into OSPF as type 1 with metric 50:

set policy-options policy-statement REDIST term 1 from protocol static
set policy-options policy-statement REDIST term 1 from route-filter 203.0.113.0/24 exact
set policy-options policy-statement REDIST term 1 then external type 1
set policy-options policy-statement REDIST term 1 then metric 50
set policy-options policy-statement REDIST term 1 then accept
set protocols ospf export REDIST

Reasoning: without then accept, the term falls through to the default reject; the route filter prevents other static routes from leaking; external type 1 changes the LSA metric behavior.

Traps

  • route-filter 10.0.0.0/8 without a modifier is exact and will not match subnets.
  • An OSPF export policy does not filter routes already learned by OSPF, and an import policy does not stop LSAs from flooding.
  • A policy term with only from conditions and no action rejects matching routes.
  • IS-IS narrow metrics cap at 63; TE and large costs need wide metrics.