28.06.2014 Views

Discussion

Discussion

Discussion

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

The route entries starting with [OSPF/10] are those learned from OSPF. The router<br />

has learned four routes from OSPF:<br />

• 192.168.17.1/32 and 192.168.18.1./32 are router loopback addresses that are<br />

the two OSPF neighbors we saw in the OSPF routing table.<br />

• 10.0.2.0/24 is a subnetwork that is the subnet between our two neighbors<br />

(which we also saw in the OSPF database).<br />

• 224.0.0.5/32 is the OSPF multicast address.<br />

The routes to the two loopback addresses show up in the routing table because the<br />

router ID is configured on the routers’ lo0 addresses, not with the set routingoptions<br />

router-id command.<br />

The value of 10 in the brackets is the JUNOS default value for the OSPF administrative<br />

distance, also called the routing preference, which is used to select what route is<br />

installed in the forwarding table when several protocols calculate routes to the same<br />

destination. A preference of 10 is the default for internal OSPF routes, which are<br />

those within the domain. The preference value for routes outside the domain that<br />

OSPF advertises is 150. You can change the preference value by configuring the<br />

preference statement for the OSPF area. The numbers following the brackets show<br />

how long the routing table has known about the route. The metric value (either 1 or<br />

2) is the cost to this address. Understanding the routing table is discussed more in<br />

Recipe 9.1.<br />

You might find it strange that a multicast address, 224.0.0.5/32, is present in the<br />

inet.0 routing table, which is the unicast routing table. This is simply a result of a<br />

JUNOS design decision. Instead of establishing a separate routing table for the few<br />

multicast routes used by routing protocols for receiving protocol packets, which are<br />

well-known addresses, the JUNOS software places these routes in the unicast routing<br />

table.<br />

You can also see just the routes learned by OSPF:<br />

aviva@RouterG> show route protocol ospf table inet.0<br />

inet.0: 14 destinations, 14 routes (14 active, 0 holddown, 0 hidden)<br />

+ = Active Route, - = Last Active, * = Both<br />

10.0.2.0/24 *[OSPF/10] 00:00:26, metric 2<br />

to 10.0.1.1 via fe-0/0/1.0<br />

> to 10.0.0.2 via fe-1/0/1.0<br />

192.168.17.1/32 *[OSPF/10] 00:00:26, metric 1<br />

> to 10.0.0.2 via fe-1/0/1.0<br />

192.168.18.1/32 *[OSPF/10] 00:00:31, metric 1<br />

> to 10.0.1.1 via fe-0/0/1.0<br />

224.0.0.5/32 *[OSPF/10] 00:00:42, metric 1<br />

MultiRecv<br />

Viewing Routes Learned by OSPF | 389<br />

This is the Title of the Book, eMatter Edition<br />

Copyright © 2008 O’Reilly & Associates, Inc. All rights reserved.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!