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Can somebody explain why we can assign link-local address FE80::1 to both interfaces? What does it give to me ?

R1(config)# interface g0/0
R1(config-if)# ipv6 address fe80::1 link-local
R1(config-if)# interface g0/1
R1(config-if)# ipv6 address fe80::1 link-local

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  • The keyword here is "scope".
    – Ricky
    Commented Oct 29, 2021 at 6:33
  • Router advertisements for IPv6 stateless address autoconfiguration need to be sent from link-local address. I would assume that this is also a reason to assign local addresses. (see rfc4861 and rfc4862)
    – Effie
    Commented Nov 4, 2021 at 20:03

2 Answers 2

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ipv6 link-local addresses are unique only on the link and traffic is never forwarded.

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  • is it enough to only have link local address, or does the router needs routable address too?
    – Effie
    Commented Oct 29, 2021 at 20:43
  • @Effie If you want to route traffic, you need routable addresses.
    – Ron Trunk
    Commented Nov 1, 2021 at 18:42
  • 1
    If I want to route traffic to end-systems, not the router?
    – Effie
    Commented Nov 2, 2021 at 16:19
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A link-local address is only used on a single link. Traffic on a link-local network is confined to that network and cannot be routed to a different network. All IPv6 interfaces use the same link-local network, so addresses on one link-local network can be the same on a different link-local network.

See RFC 4291, IP Version 6 Addressing Architecture:

2.5.6. Link-Local IPv6 Unicast Addresses Link-Local addresses are for use on a single link. Link-Local addresses have the following format:

    |   10     |
    |  bits    |         54 bits         |          64 bits           |
    +----------+-------------------------+----------------------------+
    |1111111010|           0             |       interface ID         |
    +----------+-------------------------+----------------------------+

Link-Local addresses are designed to be used for addressing on a single link for purposes such as automatic address configuration, neighbor discovery, or when no routers are present. Routers must not forward any packets with Link-Local source or destination addresses to other links.

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