© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-1 IPv6 Operations Defining and Configuring Neighbor Discovery

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-2 ICMPv6 ICMPv6 is similar to ICMPv4: Provides diagnostic and error messages Used for path MTU discovery ICMPv6 TypeICMPv6 Code ICMPv6 Data Checksum IPv6 Basic Header ICMPv6 Packet Next Header = 58 ICMPv6 Packet ICMPv6 Packet

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-3 MTU = 1300 Path MTU Discovery MTU = 1500 MTU = 1400 Packet with MTU = 1500 ICMP error: packet too big Use MTU = 1400 Packet with MTU = 1400 ICMP error: packet too big Use MTU = 1300 Packet with MTU = 1300 Path MTU = 1300 SourceDestination

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-4 Maximum Transmission Unit IPv4 –MTU >= 68 octets IPv6 –MTU >= 1280 octets –Path MTU used Frame HeaderFrame TrailerIPv6 Packet Minimum MTU = 1280 Octets Link-Layer Frame

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-5 IPv6 over Data Link Layers IPv6 is defined for most data link layers: Ethernet PPP FDDI Token Ring HDLC Nonbroadcast multiaccess ATM Frame Relay IEEE 1394

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-6 IPv6 over Ethernet IPv6 has a specific Ethernet protocol ID that is different from the protocol ID in IPv4. Destination Ethernet Address IPv6 Header and Payload0x86DD Source Ethernet Address

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0— X FC0F 17FC0F FFFE Modified EUI-64 Format A modified EUI-64 address is formed by inserting "FFFE" and “complementing” a bit identifying the uniqueness of the MAC address. where X = 1 = universally unique 0 = locally unique X = 1 Ethernet MAC Address (48 Bits) 64-Bit Version U/L Bit Modified EUI-64 Address FC0F 17FC0FFFFE FFFE

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-8 Neighbor Discovery Neighbor discovery: –Queries for duplicate address detection –Determines the link layer address of a neighbor on the same link –Finds neighbor routers on link Achieved by using ICMPv6 with IPv6 multicast

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-9 Solicited-Node Multicast Address Solicited-node address: Multicast address with a link-local scope Formed by a prefix and the rightmost 24 bits of every unicast and anycast address Prefix 0Lower 24 Interface ID FF Bits FF 24 Bits IPv6 Address Solicited-Node Multicast Address 0001

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-10 FF FF17FC0F 17FC0F FF Multicast Mapping over Ethernet IPv6 Solicited-Node Multicast Address Corresponding Ethernet Address Multicast Prefix for Ethernet Multicast 20010DB F 02C0 10FF FC0F IPv6 Address FE 17

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-11 Duplicate Address Detection ICMP type = 135 Src = 0 (::) Dst = solicited-node multicast of A Data = link-layer address of A Query = What is your link address? DAD uses neighbor solicitation to verify the existence of an address to be configured. BA

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-12 ICMP type = 136 Src = B Dst = A Data = link-layer address of B ICMP type = 135 Src = A Dst = solicited-node multicast of B Data = link-layer address of A Query = What is your link address? A and B can now exchange packets on this link. Neighbor Discovery: Neighbor Solicitation BA

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-13 Neighbor Discovery: Neighbor Solicitation (Cont.) Neighbor Advertisement Message R: router flag, indicates sender is a router S: solicited flag, indicates message sent in response to a neighbor solicitation O: override flag, indicates advertisement should override existing neighbor cache entry

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-14 Neighbor Discovery: Autoconfiguration Autoconfiguration Stateless –Uses neighbor discovery router advertisements Stateful –Uses DHCPv6 service

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-15 Routers send periodic router advertisements to the all-nodes multicast address. Router advertisement packet definitions: ICMP type = 134 Src = router link-local address Dst = all-nodes multicast address Data = options, prefix, lifetime, autoconfiguration flag Router Advertisement Neighbor Discovery: Router Advertisements Router Advertisement

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-16 Neighbor Discovery Parameters Router advertisements: Default router IPv6 network prefix Lifetime of advertisement Autoconfiguring IPv6 Hosts

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-17 Neighbor Discovery Parameters (Cont.) Router advertisements: Default router IPv6 network prefix Lifetime of advertisement Autoconfiguring IPv6 Hosts

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-18 Neighbor Discovery: Router Solicitations At boot time, nodes send router solicitations to promptly receive router advertisements. Router solicitation packet definitions: ICMP type = 133 Src = unspecified address Dst = all-routers multicast address Router Advertisement Router Solicitation

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-19 Stateless Autoconfiguration Router solicitations are sent by booting nodes to request router advertisement for configuring the interfaces. 1. Router Solicitation: ICMP type = 133 Src = :: Dst = all-routers multicast address Query = Please send router advertisement 2. Router advertisement 1. Router solicitation 2. Router Advertisement: ICMP type = 134 Src = router link-local address Dst = all-nodes multicast address Data = options, prefix, lifetime, autoconfiguration flag 2. Router advertisement

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-20 Router advertisement packet definitions: ICMP type = 134 Src = Router link-local address Dst = All-nodes multicast address Data = Two prefixes: Current prefix (to be deprecated) with short lifetime New prefix (to be used) with normal lifetime Renumbering Renumbering is achieved by modifying the router advertisement to announce the old prefix with a short lifetime and the new prefix. Router Advertisement

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-21 Value of Autoconfiguration IPv6 address autoconfiguration enables “plug-and-play.” Nodes may be deployed without a DHCPv6 server: –Mobile devices (phones, PDAs, autos) –Home electronics (TVs, DVRs, appliances) –Field telemetry (oil pipeline gauges) Autoconfiguration enables massive deployment (millions) of IPv6 nodes.

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-22 ipv6 nd prefix | default [ [ ] | [at ] [off-link] [no-autoconfig] ] router(config-if)# Used to modify prefix advertisement parameters on an interface from their default values. Cisco IOS Neighbor Discovery Command Syntax

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-23 LAN2: 2001:db8:c18:2::/64 LAN1: 2001:db8:c18:1::/64 Router Advertisement Ethernet1 Ethernet0 interface Ethernet0 ipv6 address 2001:db8:c18:1::2/64 ipv6 nd prefix 2001:db8:c18:1::/ interface Ethernet1 ipv6 address 2001:db8:c18:2::1/64 ipv6 nd prefix 2001:db8:c18:2::/ interface Ethernet0 ipv6 address 2001:db8:c18:1::1/64 ipv6 nd prefix 2001:db8:c18:1::/ Router2 Router1 Cisco IOS Command for Overriding the Neighbor Discovery Defaults Router Advertisement IPv6 Internet

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-24 LAN1: 2001:db8:c18:1::/64 LAN2: 2001:db8:c18:2::/64 Ethernet0 Ethernet1 Ethernet0 interface Ethernet0 ipv6 nd prefix 2001:db8:c18:1::/ interface Ethernet1 ipv6 nd prefix 2001:db8:c18:2::/ interface Ethernet0 ipv6 nd prefix 2001:db8:c18:1::/ Router2 Router1 Cisco IOS Command for Overriding the Neighbor Discovery Defaults (Cont.) Router Advertisement IPv6 Internet

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-25 LAN1: 2001:db8:c18:1::/64 LAN2: 2001:db8:c18:2::/64 Ethernet0 Ethernet1 Ethernet0 interface Ethernet0 ipv6 nd prefix 2001:db8:c18:1::/ ipv6 nd ra lifetime 100 interface Ethernet1 ipv6 nd prefix 2001:db8:c18:2::/ interface Ethernet0 ipv6 nd prefix 2001:db8:c18:1::/ Router2 Router1 Cisco IOS Neighbor Discovery Lifetimes Router Advertisement IPv6 Internet

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-26 Network Prefix: 2001:db8:c18:1::/64 interface Ethernet0 ipv6 nd prefix 2001:db8:c18:1::/ Host Configuration: Autoconfiguring IPv6 Hosts preferred address 2001:db8:c18:1:260:8ff:fede:8fbe Router Configuration before Renumbering: Router Advertisements Cisco IOS Network Prefix Renumbering Scenario

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-27 interface Ethernet0 ipv6 nd prefix 2001:db8:c18:1::/ ipv6 nd prefix 2001:db8:c18:2::/ New Network Prefix: 2001:db8:c18:2::/64 Deprecated Prefix: 2001:db8:c18:1::/64 Host Configuration: Autoconfiguring IPv6 Hosts deprecated address 2001:db8:c18:1:260:8ff:fede:8fbe preferred address 2001:db8:c18:2:260:8ff:fede:8fbe Router Configuration after Renumbering: Router Advertisements interface Ethernet0 ipv6 nd prefix 2001:db8:c18:1::/64 at Jul :59 Jul :59 ipv6 nd prefix 2001:sb8:c18:2::/ Cisco IOS Network Prefix Renumbering Scenario (Cont.) or:

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-28 Summary ICMP messages are used for many IPv6 functions, including path MTU discovery, neighbor discovery, and router discovery. ICMPv6 is an integral part of IPv6 but looks similar to a Layer 4 protocol, much like TCP or UDP. Path MTU is performed by nodes in an effort to determine the largest packet size they can send to a given destination. It is based on a process of sending large packets and listening for ICMPv6 error messages. Neighbor discovery is a critical process that allows neighbors to determine the link-layer address associated with a given IPv6 address. It also allows hosts to receive prefix information to configure a global-scope address and find the default router. Before a node can use an address, it must test it for uniqueness on the link. DAD is a process by which a node with a "tentative" address that it would like to use determines if that address is already in use. Autoconfiguration provides a type of network “plug-and-play,” easily supporting millions of transient nodes and enabling a network environment with support for mobile phones, field sensors, and home appliances. Cisco routers are IPv6-ready and are configured for IPv6 functions on a global and per-interface basis, depending on the function being enabled.

© 2006 Cisco Systems, Inc. All rights reserved.IP6FD v2.0—2-29