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This forwarding table is then copied to the PFE’s forwarding table:<br />

aviva@Router1> show pfe route ip prefix 172.16.14.0/24<br />

Slot 0<br />

IPv4 Route Table 0, default.0, 0x0:<br />

Destination NH IP Addr Type NH ID Interface<br />

--------------------------------- --------------- -------- ----- ---------<br />

172.16.14/24 Unilist 526570 ge-0/1/0.0<br />

Slot 1<br />

IPv4 Route Table 0, default.0, 0x0:<br />

Destination NH IP Addr Type NH ID Interface<br />

--------------------------------- --------------- -------- ----- ---------<br />

172.16.14/24 Unilist 526570 ge-0/1/0.0<br />

Both the routes are of type Unilist, which means that they are in the list of unicast<br />

next hops maintained by the Packet Forwarding Engine. The NH ID field shows the<br />

kernel’s index of the indirect next hop, which matches what you saw in the show<br />

route detail output.<br />

Even though multipath BGP selects multiple paths for forwarding and installs two<br />

paths in the forwarding table, BGP advertises only one path to its peers, which is the<br />

best path toward the destination. This is the same path that BGP would advertise if<br />

BGP load balancing were not configured.<br />

You can also use multipath BGP across IBGP peerings. An additional restriction is<br />

that the IGP metric distance to the two IBGP peers must be identical. A scenario for<br />

doing this might be to load-balance traffic across redundant paths within a POP.<br />

See Also<br />

Recipes 8.9 and 9.1<br />

13.15 Tracing BGP Protocol Traffic<br />

Problem<br />

You want to keep a running log of BGP protocol information so you can track any<br />

problems with your BGP peers.<br />

Solution<br />

When performing ongoing monitoring of BGP operations, set up tracing options (or<br />

traceoptions for short) to track BGP state changes globally for all BGP groups:<br />

[edit protocols bgp]<br />

aviva@RouterF# set traceoptions flag state detail<br />

aviva@RouterF# set traceoptions file bgp-trace world-readable<br />

To turn off BGP tracing, remove the traceoptions statement from the configuration:<br />

[edit protocols bgp]<br />

aviva@RouterF# delete traceoptions<br />

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

Copyright © 2008 O’Reilly & Associates, Inc. All rights reserved.<br />

Tracing BGP Protocol Traffic | 475

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