Summarizing Routes in OSPF

Table of contents:

Problem

You want to minimize the size of a backbone routers link-state database by summarizing the routes sent to the backbone area.

Solution

Summarize the routes that are flooded into the backbone area by the ABR:

	[edit protocols ospf]
	aviva@RouterJ# set area 0.0.0.3 area-range 10.0.0.0/16

Discussion

OSPF route summarization aggregates routes sent by nonbackbone areas to the backbone routers so that the size of their link-state databases is reduced. In this recipe, the networks in Area 0.0.0.3 are 10.0.8.1/28, 10.0.8.2/28, 10.0.13.1/28, and 10.0.13.2/28 (see Figure 12-3), which can be summarized as 10.0.0.0/24.

If we check on one of the backbone routers before configuring route summarization, we see four Type 3 (Summary) LSAs in the link-state database:

	aviva@RouterG> show ospf database
	 OSPF link state database, area 0.0.0.0
	 Type ID Adv Rtr Seq Age Opt Cksum Len
	Router 192.168.17.1 192.168.17.1 0x80000189 16 0x2 0x926e 60
	Router 192.168.18.1 192.168.18.1 0x80000124 2601 0x2 0x97cd 60
	Router *192.168.19.1 192.168.19.1 0x8000009c 126 0x2 0xb4c7 48
	Network *10.0.0.1 192.168.19.1 0x80000090 726 0x2 0x9aae 32
	Network *10.0.1.2 192.168.19.1 0x80000090 426 0x2 0x92b3 32
	Network 10.0.2.1 192.168.18.1 0x8000009b 1651 0x2 0x6cd1 32
	Summary 10.0.8.0 192.168.17.1 0x80000009 16 0x2 0xa62f 28
	Summary 10.0.13.0 192.168.17.1 0x80000002 16 0x2 0xa8c 28
	Summary 192.168.15.1 192.168.17.1 0x80000002 16 0x2 0x1510 28
	Summary 192.168.16.1 192.168.17.1 0x80000002 16 0x2 0x7de7 28
	ASBRSum 192.168.15.1 192.168.17.1 0x80000002 16 0x2 0x71d 28
	 
OSPF AS SCOPE link state database
	 Type ID Adv Rtr Seq Age Opt Cksum Len
	Extern 10.0.15.0 192.168.15.1 0x80000001 161 0x2 0x3f01 36
	Extern 172.19.121.0 192.168.15.1 0x80000001 161 0x2 0x859a 36
	Extern 172.19.121.0 192.168.17.1 0x80000003 472 0x2 0x73a8 36
	Extern 192.168.15.1 192.168.15.1 0x80000001 161 0x2 0x6d9 36
	Extern 192.168.17.1 192.168.17.1 0x80000003 240 0x2 0xddfb 36

After the ABR for Area 0.0.0.3 begins aggregating the routes, the number of Type 3 LSAs sent to the backbone area decreases to three, and two LSAs from that area, 10.0.8.0 and 10.0.13.0, are combined into one, 10.0.0.0:

	aviva@RouterG> show 
ospf database
	 OSPF link state database, area 0.0.0.0
	 Type ID Adv Rtr Seq Age Opt Cksum Len
	Router 192.168.17.1 192.168.17.1 0x8000018c 20 0x2 0x8c71 60
	Router 192.168.18.1 192.168.18.1 0x80000124 2842 0x2 0x97cd 60
	Router *192.168.19.1 192.168.19.1 0x8000009c 367 0x2 0xb4c7 48
	Network *10.0.0.1 192.168.19.1 0x80000091 67 0x2 0x98af 32
	Network *10.0.1.2 192.168.19.1 0x80000090 667 0x2 0x92b3 32
	Network 10.0.2.1 192.168.18.1 0x8000009b 1892 0x2 0x6cd1 32
	Summary 10.0.0.0 192.168.17.1 0x80000001 20 0x2 0xf59f 28
	Summary 192.168.15.1 192.168.17.1 0x80000005 20 0x2 0xf13 28
	Summary 192.168.16.1 192.168.17.1 0x80000005 20 0x2 0x77ea 28
	ASBRSum 192.168.15.1 192.168.17.1 0x80000005 20 0x2 0x120 28
	 OSPF AS SCOPE link state database
	Type ID Adv Rtr Seq Age Opt Cksum Len
	Extern 10.0.15.0 192.168.15.1 0x80000002 10 0x2 0x3d02 36
	Extern 172.19.121.0 192.168.15.1 0x80000001 402 0x2 0x859a 36
	Extern 172.19.121.0 192.168.17.1 0x80000004 117 0x2 0x71a9 36
	Extern 192.168.15.1 192.168.15.1 0x80000001 402 0x2 0x6d9 36
	Extern 192.168.17.1 192.168.17.1 0x80000003 481 0x2 0xddfb 36


Router Configuration and File Management

Basic Router Security and Access Control

IPSec

SNMP

Logging

NTP

Router Interfaces

IP Routing

Routing Policy and Firewall Filters

RIP

IS-IS

OSPF

BGP

MPLS

VPNs

IP Multicast



JUNOS Cookbook
Junos Cookbook (Cookbooks (OReilly))
ISBN: 0596100140
EAN: 2147483647
Year: 2007
Pages: 290
Authors: Aviva Garrett

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