Enterasys Networks X-PeditionTM manual LSA Type 3 and 5 Summarization, Ospf Database Overflow

IP Routing Protocols

•Incremental SPF is always enabled. SPF calculation can be changed with timers spf

•Hello wait intervals with ip ospf dead-intervaland ip ospf hello-intervalas well as the poll timer to set up adjacencies as quickly as possible with ip ospf poll-timer

•Retransmission and link-state update intervals with ip ospf retransmit-intervaland ip ospf transmit-delay

•A host of statistical display commands including: show ip ospf border routers, show ip ospf database, show ip ospf interface, show ip ospf neighbor, show ip ospf virtual links, show ip protocols, and show ip route

LSA Type 3 and 5 Summarization

The XSR supports LSA Type 3 and 5 summarization using the area range advertise and summary-addresscommands, respectively. Type 3 LSAs (intra routes) are summarized by an Area Border Router then injected into other areas and furnished a unique Link-State ID (Appendix E Processing) as well as the highest metric of the included intra-area routes. Further, the XSR installs a discard route for any active summary range of routes, defined as including at least one intra route being leaked into the area. Conversely, specifying the not-advertisevalue causes undesired aggregated Type 3 LSAs to be discarded, and when a summary range becomes inactive, the discard route is dropped.

Note: Summary ranges may overlap. The most specific range activates for a locally sourced route,

Type 5 LSA summarization groups locally sourced routes which have been redistributed from other protocols. The XSR’s Type 5 summarization is similar to Type 3 aggregation in terms of discard routes, Appendix E processing, overlapping, and not-advertisebehavior. Additionally:

•The XSR will not summarize Type 7 to Type 5 translations.

•The XSR produce a Type 5 LSA for active summary ranges. If a NSSA area exists, a Type 7 LSA will be produced for each NSSA area.

•The XSR should not be subjected to needless re-origination of Type 5 LSAs. For example, importing locally sourced routes which do not alter a summary’s type/cost will not re- originate the summary LSA.

•Type 5 LSAs generated by translation may supplant a Type 5 LSA originating from a local source. This will not affect what is being generated into a NSSA because translations are not advertised there.

•If for a given prefix, both a summary and a locally sourced route exist, the summary will be considered the better route even if the summary includes only that locally sourced route.

OSPF Database Overflow

A router sometimes cannot maintain the Link-State database in its entirety, typically, because the database has overflowed due to importing many external Type 5 LSA routes into OSPF. You can avert this issue by properly configuring OSPF routers into stub areas or NSSAs since AS-external LSAs are omitted from this type of Link-State database. But, with an unexpected database overflow, there is not enough time to perform this type of isolation.

The XSR’s database-overflowcommand controls this problem by limiting the number of Type 5 LSAs it imports and others as well: Types 1 through 4, 7, and 10. The command also can set a warning of a pending overflow and set an interval in which to exit overflow.

XSR User’s Guide 5-15