Tuesday, March 21, 2006

 

Installation of route to Null0 for FE80::/10 prefix. (Question #45)

A router running IPv6 has the following configuration

ipv6 unicast-routing
!
interface Ethernet0
ipv6 address autoconfig
no keepalive


Now consider the following output from that router

R1#sh ipv6 interface brief
Ethernet0 [up/up]
FE80::A8BB:CCFF:FE00:8300

R1#sh ipv6 route
IPv6 Routing Table - 2 entries
Codes: C - Connected, L - Local, S - Static, R - RIP, B - BGP
U - Per-user Static route
I1 - ISIS L1, I2 - ISIS L2, IA - ISIS interarea
O - OSPF intra, OI - OSPF inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2
L FE80::/10 [0/0]
via ::, Null0
L FF00::/8 [0/0]
via ::, Null0
R1#


What is the rationale for the automatic installation of a route to Null0 for the FE80::/10 prefix which happens to match the IPv6 address that the ethernet interface on the router is auto-configured with?

Comments:
Autoconfiguration will yield a link-local
address with the FE80::/10 prefix. This
ip address cannot be forwarded - routed beyond this
local-link network. Installing a route to
null will prevent the routing of such an
address range.
 
Yes, that's the correct explanation.
 
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