Difference between revisions of "Link-Local IPv6 Address"

Revision as of 08:32, 13 June 2011

Link-Local

IPv6 Address Type:	Link-Local
Prefix:	fe80::/10
Local Routeable:	No
Global Routeable:	No
Global Unique:	No
Example:	FE80::21B:D4FF:FE0F:8CA2
IPv4 Equivalent:	169.254.0.0/16 Link-Local
Described in:	rfc4291

Explanation

These addresses are used on a single link or a non-routed common access network, such as an Ethernet LAN.

They do not need to be unique outside of that link.

Link-local addresses may appear as the source or destination of an IPv6 packet.

Routers must not forward IPv6 packets if the source or destination contains a link-local address.

IPv6 Address Types

IPv6 Link-Local Addresses

Link-Local Addresses are used by Nodes to communicate to other Nodes on the same Link. Link-Local addresses are not Routeable.

Windows 7 Link-Local Address Example

Format of Link-Local address

IPv6#<input>sh ipv6 int fa0/0</input>
FastEthernet0/0 is up, line protocol is up
  IPv6 is enabled, <notice>link-local address is FE80::21B:D4FF:FE0F:8CA2</notice>
  No Virtual link-local address(es):
  Description: Outside: Internet connection to ISP
  Global unicast address(es):
    2001:16D8:DD85:146::2, subnet is 2001:16D8:DD85:146::/64
  Joined group address(es):
    FF02::1
    FF02::2
    FF02::D
    FF02::16
    FF02::1:FF00:2
    FF02::1:FF0F:8CA2
  MTU is 1500 bytes
  ICMP error messages limited to one every 100 milliseconds
  ICMP redirects are enabled
  ICMP unreachables are sent
  ND DAD is enabled, number of DAD attempts: 1
  ND reachable time is 30000 milliseconds
  Hosts use stateless autoconfig for addresses.

Example why originating interface is important

Notice in the example below, we telnet to the Heimdal Router - the very same we're on - even I know that the Link-Local address FE80::218:18FF:FE7C:B440 is on a neighboring Router called Campus1.

<notice>Heimdal</notice>#<input>telnet FE80::218:18FF:FE7C:B440</input>
Trying FE80::218:18FF:FE7C:B440 ... Open
 !!!Netadmin Please upgrade the network security!!!
banner motd

User Access Verification

Password:
<notice>Heimdal</notice>><input>exit</input>

[Connection to FE80::218:18FF:FE7C:B440 closed by foreign host]

Link-Local addresses are local on a link. We need to tell on which interface the Link-Address are on. First we need to find the interface on which the address resides.

Heimdal#<input>show ipv6 neighbor | inc B440</input>
FE80::218:18FF:FE7C:B440                    0 0018.187c.b440  STALE <notice>Vl1</notice>

In the output in previous command, it's seen that the Link-Local address lives in Vlan1. Now we telnet from that source-interface - and Voila everything works as expected.

 
<notice>Heimdal</notice>#<input>telnet FE80::218:18FF:FE7C:B440 /source-interface vlan1</input>
Trying FE80::218:18FF:FE7C:B440 ... Open
 !!!Netadmin please upgrade Network Security!!!
banner motd

User Access Verification

Password:
<notice>Campus1</notice>>

@@ Line 16: / Line 16: @@
 Routers must not forward IPv6 packets if the source or destination contains a link-local address.
 }}
-=IPv6 Link-Local Addresses=
+==IPv6 Link-Local Addresses==
 Link-Local Addresses are used by Nodes to communicate to other Nodes on the same Link. Link-Local addresses are ''not'' Routeable.
 [[Image:Link-Local Address Windows 7.PNG|left|400px|thumb|Windows 7 Link-Local Address Example]]
@@ Line 44: / Line 44: @@
 </source>
 {{Source cli}}
-=Example why originating interface is important=
+==Example why originating interface is important==
 Notice in the example below, we telnet to the Heimdal Router - the very same we're on - even I know that the Link-Local address FE80::218:18FF:FE7C:B440 is on a neighboring Router called Campus1.
 <source lang=cli>