R&S Quick Notes – IGP’s

RIP

• Know your filters: Offset-list, Distribute-lists, distance command.
• With filters read carefully: “between 25 & 45″ or “from 25 to 45″.
• Know your prefix-lists or alternatively using ACL's instead.
• “passive interface” command, ONLY stops the sending of updates out the interface. Interface will still receive and process those updates. Passive interfaces will still be advertised in other updates.

EIGRP

• Advertising a default route out one interface: “ip summary-address eigrp [AD] 0.0.0.0 0.0.0.0″
• To see if a neighbor is configured as STUB, “show ip eigrp neighbors [detail]” as look for ‘CONNECTED SUMMARY'

• On frame-relay multipoint interfaces, don't forget to disable split-horizon.
• External EIGRP routes AD (admin distance = 170) can NOT be changed on per prefix basis.
• Metric weight values:
1 0 1 0 0 = Default
0 0 1 0 0 = Only DLY
1 0 0 0 0 = Only BW
3 0 1 0 0 = BW has 3 times more weight reference than DLY
• Metric formula:

Metric = ((10⁷ / BW) + (DLY/10) ) * 256

OSPF

• The Neighbor IP used with OSPF distance command is the Neighbors Router-ID.
• “area range” summarize type 3 LSA'.
• “summary-address” summarize type 5 & 7 LSA's.
• Auto-cost reference BW (Default = 100mb), formula = Ref-BW/Int-Bw.
• Switches do no support the interface command “ip ospf {pid} area {area-id}” .
• OSPF path selection: O > O*IA > O*E1 > O*E2.
• Using E1 metric type : Packets will be routed out the closest exit point of the network.
• Using E2 metric type : If you want packets to exit your network at the closest point to their external destination.
• Don't forget with hub and spoke topology, “ip ospf priority 0″.
• PITFALL, when forbid to use RID, Loopbacks created later on might change the DR on you network after a reload.
• PITFALL, when forbid to use RID, Later requested to configure the same loopback on two routers, could break your adjacencies, as two router cant peer with the same RID.
• “no capability transit” – Mimics OSPFv1 behaviour for all data traffic to pass through Area-0.
• “max-metric” – Configures OSPF stub configurations
• “max-lsa” – Limit amount of non-local LSA's
• “timers throttle lsa all” – Slow down update rate.
• “timers pacing lsa-group” – Group more LSA's together in updates.
• “no ip ospf flood-reduction” – Disables every 30-min LSA DB refresh.
• “ip ospf database filter all out” – Breaks RFC, Stop sending LSA's, but still receive LSA's

by CCIE 24163