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gre<br />

up<br />

ipip<br />

up<br />

lo0 up up<br />

lo0.0 up up inet 127.0.0.1 --> 0/0.<br />

lo0.16385 up up inet<br />

inet6 fe80::2a0:a5ff:fe12:3ed5<br />

lsi up up<br />

mtun up up<br />

pimd up up<br />

pime up up<br />

tap up up<br />

Description<br />

Toward the end of the show interfaces output, you see a number of interfaces that<br />

don’t correspond to any of the physical interfaces you have configured on the router.<br />

Most of these special interfaces are internal interfaces that are created and used by<br />

the JUNOS software to route traffic within the router. The fxp0 (the out-of-band<br />

management) and loopback (lo0) interfaces, which are configurable, provide connection<br />

to the Routing Engine.<br />

The fxp1 interface is an internal Ethernet interface that connects the Packet Forwarding<br />

Engine (all the chassis hardware components) to the Routing Engine, which handles<br />

all routing protocol operations. The output in this recipe shows that fxp1 has<br />

an internal IPv4 address of 10.0.0.5/8 and a Trivial Network Protocol (TNP)<br />

address of 5. JUNOS software uses the proprietary TNP internally to communicate<br />

between the forwarding and Routing Engines.<br />

As a side note, the fxp0 and fxp1 interfaces take their names from the FreeBSD fxp<br />

Ethernet device driver.<br />

On J-series routers, the Packet Forwarding Engine and Routing Engine functionality<br />

is on the same chip, so there is no fxp1 interface or its equivalent. Also, because the<br />

fe-0/0/0 serves the function of the fxp0 interface, it isn’t listed at the end of the show<br />

interfaces terse command output with the nonconfigurable interfaces:<br />

aviva@RouterA> show interfaces terse<br />

Interface Admin Link Proto Local Remote<br />

fe-0/0/0 up up<br />

fe-0/0/0.0 up up inet 10.0.16.1/24<br />

172.19.121.142/24<br />

gr-0/0/0 up up<br />

ip-0/0/0 up up<br />

ls-0/0/0 up up<br />

lt-0/0/0 up up<br />

mt-0/0/0 up up<br />

pd-0/0/0 up up<br />

pe-0/0/0 up up<br />

sp-0/0/0 up up<br />

sp-0/0/0.16383 up up inet<br />

fe-0/0/1 up up<br />

Dealing with Nonconfigurable Interfaces | 241<br />

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

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

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