Understand Open Shortest Path First (ospf) Design Guide

router ospf
, and has the syntax:
[no] compatible rfc1583
The default parameter is compatible with 
RFC 1583
. This command is available in these versions
of Cisco IOS®:
12.1(03)DC
●
12.1(03)DB
●
12.001(001.003) - 12.1 Mainline
●
12.1(01.03)T - 12.1 T-Train
●

---

12.000(010.004) - 12.0 Mainline
●
12.1(01.03)E - 12.1 E-Train
●
12.1(01.03)EC
●
12.0(10.05)W05(18.00.10)
●
12.0(10.05)SC
●
External Route Summarization
External route summarization is specific to external routes that are injected into OSPF via
redistribution. Also, make sure that external ranges that are summarized are contiguous.
Summarization of overlapped ranges from two different routers could cause packets to be sent to
the wrong destination. Summarization is done via the 
router ospf
subcommand:
summary-address ip-address mask
This command is effective only on ASBR redistribution into OSPF.
In this diagram, RTA and RTD inject external routes into OSPF by redistribution. RTA injects
subnets in the range 128.213.64-95 and RTD injects subnets in the range 128.213.96-127. To
summarize the subnets into one range on each router:
RTA#
router ospf 100
summary-address 172.16.0.64 255.255.224.0
redistribute bgp 50 metric 1000 subnets
RTD#
router ospf 100
summary-address 172.16.0.96 255.255.224.0
redistribute bgp 20 metric 1000 subnets

---

This causes RTA to generate one external route 172.16.0.64 255.255.224.0 and causes RTD to
generate 172.16.0.96 255.255.224.0.
Note that the 
summary-address
command has no effect if used on RTB because RTB does not
perform the redistribution into OSPF.