1. 1 CMPT 471 Networking II ICMPv6 © Janice Regan, 2012

2. Link local - site local  Link local addresses can only be used with a direct physical connection (FE80::) (addresses reached by IPv4 broadcast)  Site local addresses can be routed within a local site internet, but not onto the Internet (FEC0::) (similar to IPv4 reserved addresses like those on network 192.168.0.0) © Janice Regan, 2012 2

3. 3 ICMPv6 message header format  ICMPv6 message header format is the same as ICMPv4  Each ICMP message has its own format, but all start with the same three fields  A type field (1 octet) indicating which type of ICMP message follows  A 1 octet code following the type that further defines the message (see text for list) For example type specifies destination unreachable, code specifies router or host  The 3 rd common field is a 2 octet checksum. The checksum is calculated the same way as the IPv4 checksum, including the entire ICPM PDU in the calculation

4. Types and codes DIFFERENT  The types and codes for ICMPv6 messages are completely different for those of ICMPv4 messages  Many of the same messages are available but their types and codes are now different  Messages are divided into two groups Errors (message numbers 1 to 127) Information messages (message numbers ≥ 128) © Janice Regan, 2012 4

5. Some types and codes (error) © Janice Regan, 2012 5 CODE 0- no route to destination 1-communication administratively prohibited 3-address unreachable 4-port unreachable 0 0-hop limit exceeded 1-fragment reassembly time exceeded 0-erroneous header field encountered 1-next header type not recognized 2-unrecognized option Message number (message number for errors 1-127) 1 (destination unreachable) 2 (packet too big) 3 (time exceeded) 4 (parameter problem

6. Some more types (information) © Janice Regan, 2012 6 Message number 128 Echo request 129 Echo reply 133 Router solicitation 134 Router Advertisement 135 Neighbor solicitation 136 Neighbor advertisement 137 Redirect message

7. Destination Unreachable  ICMPv6 Destination Unreachable message is sent when a router cannot forward the packet to (or toward) the destination because  It has no route to the destination network in its routing table  It cannot find a requested host on its local network  There is no server to deal with the incoming request  The IPv6 address or port is administratively blocked © Janice Regan, 2012 7

8. ICMPv6 Destination Unreachable © Janice Regan, 2012 8 TYPE (1)CODE 0,1,2, or 3 CHECKSUM unused As much of invoking packet as will fit without the resulting ICMPv6 packet exceeding the minimum IPv6 MTU of 1280 VERS 6 TRAFFIC CLASS FLOW LABEL PAYLOAD LENGTH NEXT HEADER HOP LIMIT IPv6 source address IPv6 destination address IPv6 header Destination unreachable Message (ICMPv6)

9. Destination unreachable: codes 0. No route to destination: No entry in routing table. that goes to destination network and no default route 1. Administratively Blocked: may be sent from a firewall that cannot forward a packet or if a host accepts only authenticated echo requests and receives on that is not authenticated 2. Address: cannot resolve network address, router on destination network cannot find requested host 3. Port: no listening server No message equivalent to IPv4 source quench © Janice Regan, 2012 9

10. Packet too big  Sent by a router that cannot forward a packet because it is larger than the MTU of the destination network.  Used as part of the MTU discovery process (source asks: how big should the packets I send be?)  Packet too big message includes a field for the MTU of the network that the packet could not enter (4 byte field after checksum, before data) © Janice Regan, 2012 10

11. ICMPv6 TOO BIG message © Janice Regan, 2012 11 TYPE (2)CODE 0CHECKSUM MTU of next network (the network with smaller MTU that prevented the packet being forwarded) As much of invoking packet as will fit without the resulting ICMPv6 packet exceeding the minimum IPv6 MTU of 1280 VERS 6 TRAFFIC CLASS FLOW LABEL PAYLOAD LENGTH NEXT HEADER HOP LIMIT IPv6 source address IPv6 destination address IPv6 header TOO BIG Message (ICMPv6)

12. MTU discovery  Assume MTU should be the size on the interface the packet leaves the source through  If the packet is too large at an intermediate router, that router drops the packet and sends the source a packet too big message  Host now sends data with the smaller MTU  Process in previous 3 steps can be repeated  Host never sends with MTU below 1280 bytes © Janice Regan, 2012 12

13. MTU discovery © Janice Regan, 2012 13 NET 3 MTU 1280 NET 3 MTU 1500 NET 2 MTU 1350 ICMP TOO BIG message MTU = 1350 ICMP TOO BIG message MTU =1280 IP packet MTU = 1500 IP packet MTU = 1350 IP packet MTU =1280

14. Time exceeded message  Sent by a router when the lifetime of a packet becomes 0  Two possible situations  Too many hops  Waited too long for reassembly  CODE = 2: When fragments do not arrive by the time the reassembly time expires, a time exceeded message will be sent to the source © Janice Regan, 2012 14

15. Time exceeded: hop count 0  Hop count is decremented at each router  When hop count is 0 lifetime has expired  CODE=1  When decrementing the hop count results in a hop count of zero the packet is dropped and a time exceeded message is sent to the source  When a packet arrives at a router and hop count = 0, the packet is dropped and a time exceeded message is sent to the source © Janice Regan, 2012 15

16. ICMPv6 time exceeded © Janice Regan, 2012 16 TYPE (2)CODE 0CHECKSUM MTU of next network (the network with smaller MTU that prevented the packet being forwarded) As much of invoking packet as will fit without the resulting ICMPv6 packet exceeding the minimum IPv6 MTU of 1280 VERS 6 TRAFFIC CLASS FLOW LABEL PAYLOAD LENGTH NEXT HEADER HOP LIMIT IPv6 source address IPv6 destination address IPv6 header Time exceeded Message (ICMPv6)

17. traceroute6  The traceroute6 command is an example of the use of the time exceeded message  A UDP packet with a hop count of 1 is sent  The first router reached sends back a time exceeded message  A packet with a hop count of 2 is sent  The second router in the path sends back a time exceeded message  This is repeated, incrementing the hop count by 1 until the packet reaches its destination  Ubuntu sends 3 copies of each packet sent in the description above © Janice Regan, 2012 17

18. Echo Reply Echo Request  Used to test reachability of hosts  Message format same as IPv4 (but with different type)  Identifier and sequence number still used to match reply with its request  In IPv4 not authenticated, can be authenticated in IPv6 (verify source)  Improves security © Janice Regan, 2012 18

19. ICMPv6 echo request/reply © Janice Regan, 2012 19 TYPE (128/129)CODE 0CHECKSUM INDENTIFIER As much of invoking packet as will fit without the resulting ICMPv6 packet exceeding the minimum IPv6 MTU of 1280 VERS 6 TRAFFIC CLASS FLOW LABEL PAYLOAD LENGTH NEXT HEADER HOP LIMIT IPv6 source address IPv6 destination address IPv6 header Echo request/reply Message (ICMPv6) SEQUENCE NUMBER

20. ping6 testing reachability  The ping6 command for testing the reachability of other hosts is an example of the use of echo request/reply pairs  Requests and replies are matched using the identifier field and sequence number field (both fields are identical for a matching reply and request)  If a matching reply is received host is reachable  If no reply is received the host being “pinged” is not reachable © Janice Regan, 2012 20

21. © Janice Regan, 2012 21 From the TCP/IP Guide (online)

22. Neighbor Discovery protocol  We have already discussed a part of the neighbor Discovery protocol that replaces the ARP protocol and gratuitous ARP for IPv4.  Address resolution  Duplicate address detection  And additions to these protocol also adds some additional functionality used in these tasks  Neighbor unreachability © Janice Regan, 2012 22

23. Neighbor solicitation (NS) message © Janice Regan, 2012 23 TYPE (135)CODE 0CHECKSUM RESERVED (set to 0) IPv6 TARGET ADDRESS (link local IP ADDRESS of B) OPTIONS (VARIABLE LENGTH Ethernet Address of source host A. VERS 6 TRAFFIC CLASS FLOW LABEL PAYLOAD LENGTH NEXT HEADER HOP LIMIT 255 IPv6 source address (address of A) IPv6 destination address (solicited-node multicast address of B) IPv6 header Neighbor solicitation Message (ICMP)

24. Neighbor advertisement (NA) © Janice Regan, 2012 24 TYPE (136)CODE 0CHECKSUM RESERVED (set to 0) IPv6 TARGET ADDRESS (Copied from solicitation) OPTIONS (VARIABLE LENGTH) Ethernet Address of source host (host B). VERS 6 TRAFFIC CLASS FLOW LABEL PAYLOAD LENGTH NEXT HEADER HOP LIMIT 255 IPv6 source address IPv6 destination address IP header Neighbor solicitation Message (ICMP) R|S|0

25. Router Discovery: Uses  Router solicitation (RS) and Router advertisement (RA) messages are used to  Help hosts find the routers on the local network segment  Help hosts Determine the range of addresses in the local network segment (prefix discovery)  Supporting auto-config of IPv6 addresses  Help hosts discover MTU of the local segment  Help determine next hop destination © Janice Regan, 2012 25

26. © Janice Regan, 2012 26 From the TCP/IP Guide (online)

27. Router Advertisement  RAs tell hosts on the network how to find the routers on the network and some properties of the networks to which they are attached  Periodic RAs are usually sent at regular intervals. They are sent to all hosts on the network (sent to all hosts multicast address)  A responding Ra is sent to reply to RS  Host’s use RAs,  Routers ignore all received RAs. © Janice Regan, 2012 27

28. © Janice Regan, 2012 28 IPv6: information in RA (1)  Information in RAs support  Router Discovery: How hosts locate routers that reside on an attached link.  Prefix Discovery: How hosts discover the set of address prefixes that define which destinations are on-link for an attached link. (Nodes use prefixes to distinguish destinations that reside on-link from those only reachable through a router.) From RFC 2461

29. © Janice Regan, 2012 29 IPv6: information in RA (2)  Information in RAs support  Address Auto configuration: How nodes automatically configure an address for an interface.  Address resolution: How nodes determine the link-layer address of an on-link destination (e.g., a neighbor) given only the destination's IP address. (supply needed prefix information) From RFC 2461

30. © Janice Regan, 2012 30 IPv6: information in RA (3)  Information in RAs supports  Next-hop determination: The algorithm for mapping an IP destination address into the IP address of the neighbor to which traffic for the destination should be sent. The next- hop can be a router or the destination itself.  Parameter Discovery: How a node learns such link parameters as the link MTU or such Internet parameters as the hop limit value to place in outgoing packets. From RFC 2461

31. © Janice Regan, 2012 31 Improvements over IPv4  RAs carry link-layer addresses  No additional packet exchange is needed to resolve the router's link-layer address. (ARP not needed)  RAs carry prefixes for a link  There is no need for mask request/reply messages to obtain subnet or network sizes (masks)  RAs enable Address Auto-configuration.  RAs can advertise a link MTU  Hosts use this MTU on the link,  ensures that all nodes on the link use the same MTU From RFC 2461

32. Periodic Router Advertisement  Periodic RAs tell hosts on the network how to find the routers on the network and some properties of the networks to which they are attached  Periodic RA’s are usually sent at regular intervals. They are sent to all hosts on the network (sent to all hosts multicast address) © Janice Regan, 2012 32

33. Default Router: Router lifetime  A default router is a router that is willing to forward packets originating on the network segment receiving the RA.  Router Lifetime The lifetime associated with a default router entry in the cache in units of seconds (≤9000s). Default value is 3.  A router which is not willing to be a default router will advertise a lifetime of 0 © Janice Regan, 2012 33

34. Reply: Router advertisement © Janice Regan, 2012 34 TYPE (134)CODE 0 CHECKSUM RESERVED RETRANSMISSION TIMER (time in milliseconds between retransmission of NS messages). VERS 6 TRAFFIC CLASS FLOW LABEL PAYLOAD LENGTH NEXT HEADER HOP LIMIT 255 IPv6 source address (link local address of sending interface) IPv6 destination address (all nodes multicast address) IP header Router solicitation Message (ICMP) Flags Cur Hop Limit ROUTER LIFETIME OPTIONS (VARIABLE LENGTH includes link layer address of sending interface, prefix information may include MTU REACHABLE TIMER ≤1hr (time node assumes neighbor is reachable)

35. Reachable Timer  Reachable Time:. The number of milliseconds, that a node assumes a neighbor is reachable (after receiving a reachability confirmation)  Used by neighbor unreachability detection.  Applies to both hosts and routers  Must be < 1hr (3,600,000 millisecond) © Janice Regan, 201 35

36. Retransmission Timer  Retransmission Timer : The number of milliseconds, between retransmitted Neighbor Solicitation messages. (default 0, unspecified, do not change)  Used by neighbor unreachability detection  Use by address resolution  Default value in RA is 0, which means unspecified, © Janice Regan, 2012 36

37. Router Advertisement Flags  M: managed address configuration  When set indicates addresses supplied by DHCPv6  O: other configuration flag  Other configuration information (e.g. DNS info) is available from the DHCPv6 server  Redundant if M flag is set  H: Mobile Home agent flag  Allows continued connectivity when moving from one connection to internet to another, routing packets from home location to present location © Janice Regan, 2012 37

38. Router Advertisement Flags  PRF (2bits) Router selection preference  Optional, administrator configured preference, helps multi homed host pick different preferred routers available on different links  P: Neighbor Discovery Proxy Flag  Proxy for cases when bridging is not possible © Janice Regan, 2012 38

39. Router advertisement options Option format OPTIONS  Link layer address  MTU  Prefix © Janice Regan, 2012 39 TYPELENGTHDATA (variable length)

40. © Janice Regan, 2012 40 Router/Parameter/Prefix Discovery  A booting host does not want to wait for the next periodic router advertisement  A booting host can send a router solicitation (RS) message to the all routers multicast address to prompt an immediate RA.  The default routers on the local link will each reply with an immediate RA  The information in these RAs will allow the booting host to discover the routers, parameters, and prefixes for the local network segment

41. Router solicitation message © Janice Regan, 2012 41 TYPE (133)CODE 0CHECKSUM RESERVED (set to 0) OPTIONS (VARIABLE LENGTH Ethernet Address of source the sending host. VERS 6 TRAFFIC CLASS FLOW LABEL PAYLOAD LENGTH NEXT HEADER HOP LIMIT 255 IPv6 source address (IPv6 address of sending interface) IPv6 destination address (all-routers multicast address) IPv6 header Router solicitation Message (ICMP)

42. Router Solicitation  Sent by a host to determine where the routers on the local network are and parameters to use  When a host needs this information NOW not at the end of the next interval (which may be several minutes)  Receiving a RS will cause the default routers to unicast a router advertisement to the requestor  Receiving a RS will reset the routers periodic transmission timer (next RA will be 1 period after reception of the RS) © Janice Regan, 2012 42

43. Reply: Router advertisement © Janice Regan, 2012 43 TYPE (134)CODE 0 CHECKSUM RESERVED RETRANSMISSION TIMER (time in milliseconds between retransmission of NS messages). VERS 6 TRAFFIC CLASS FLOW LABEL PAYLOAD LENGTH NEXT HEADER HOP LIMIT 255 IPv6 source address (link local address of sending interface) IPv6 destination address (source address of the RS being replied to) IP header Router solicitation Message (ICMP) Flags Cur Hop Limit ROUTER LIFETIME OPTIONS (VARIABLE LENGTH includes link layer address of sending interface, prefix information may include MTU REACHABLE TIMER ≤1hr (time node assumes neighbor is reachable)

44. Prefix Discovery  How a host determines the set of prefixes that are on-link, the size and initial address of each range of valid addresses (accessible without going through a router)  Prefixes sent as part of the options in the RA tell us the on link addresses that are available  How are the prefixes sent in the RA? © Janice Regan, 2012 44

45. What a prefix option looks like © Janice Regan, 2012 45 TYPE 3LENGTH 4PREFIX LENGTH |L|A| RESERVED VALID LIFETIME (time in seconds after RA is sent that the prefix is valid) PREFERRED LIFETIME RESERVED (both reserved fields must be all 0) PREFIX (PREFIX LENGTH bits of the binary digits in the prefix of the IP address, followed by 128-PREFIXLENGTH zeros) L Flag is set when prefix can be used to determine if addresses are on link A Flag is set when prefix can be used for autonomous address configuration A lifetime of all 1’s represents infinity

46. Prefix discovery  Each router should include all prefixes it supports on the local link in the options field of the RA.  Prefix options with the L flag sent are available on link  Host can combine prefixes with L bit set from the RA’s of all routers to determine all available prefixes on the local link © Janice Regan, 2012 46

47. Parameter Discovery  How a node learns IP and link parameters used to send packets  link parameters as such as the link MTU to determine size of packets to send the retransmission time for NS messages Router lifetime Determine approach to configuration (M flag)  Internet parameters such as the hop limit value to place in outgoing packets. (from the Cur Hop limit field in the RA) © Janice Regan, 2012 47

48. © Janice Regan, 2012 48 Parameter Discovery: uses  Router announcements allow one to  Choose stateful configuration (DHCP M flag 1)  Or choose stateless auto configuration of addresses (M flag 0)  Update values such as Cur Hop Limit Reachable Time, and Retransmission Timer, MTU. If the value given is 0 this means that the existing values should continue to be used, NOT that values should be set to the default or to 0  Immediately send to router after receiving and processing RA because Link local IP addresses and hardware level addresses of the router are provided

49. Updating parameters  A router may send a RA to update any parameter/option that can have only one value  If a different value is given in the RA that the host is presently using, the value the host is using should be updated.  Some parameters (Cur Hop limit, Reachable Time and Retransmission Timer) can be given the value 0 (unspecified). This means that the current value should continue to be used. © Janice Regan, 2012 49

50. VALID Auto configuration outline © Janice Regan, 2012 50 TENTATIVE PREFERRED Normal operation DEPRECATED existing connections should use new connections might not INVALID INIT Generate address start timers (preferred lifetime, valid lifetime) Verify address With DAD\ Timers restarted by arrival of RA Or DHCPv6 renewal Preferred lifetime expires valid lifetime expires RA received

51. © Janice Regan, 2012 51 IPv6 auto configuration (1)  To make it easier to connect to a network IPv6 provides a process for auto configuration of IP address (and more) for a given node  When a node connects to the network it constructs a link local address (tentative address)

52. © Janice Regan, 2012 52 Construction of address  When a node connects to the network it constructs a link local address (tentative address)  The address begins with the link local prefix fe80::0/64 (link local address starts with 1111 1110 10 or fe80 followed by 54 0’s )  The last 64 bits will contain a modified Ethernet address of the node. The 64 bits will consist of  The first 24 bits of the Ethernet address  The Intermediate 16 bits will be FFFE (if the IEEE 802 algorithm is used)  The final 24 bits of the Ethernet address

53. © Janice Regan, 2012 53 IPv6 auto configuration (2)  To make it easier to connect to a network IPv6 provides a process for auto configuration of IP address (and more) for a given node 2. Node checks address using DAD  sends NS to solicited node multicast address  If a NA is received stop (NEED MANUAL CONFIG)  Otherwise assign the link local address to the interface

54. © Janice Regan, 2012 54 DAD details .  The next step is duplicate address detection (DAD, one of the parts of the neighbor discover protocol).  Some vendors ship multiple interfaces with the same Ethernet address, or units with configurable addresses, there is a finite chance that the constructed link local address is already in use.  A neighbor solicitation message with type 135 is sent to the tentative unicast address (source address 0::0)  If there is already a host with the tentative address it will reply to the neighbor solicitation message with a neighbor advertisement message multicast to all nodes multicast address. This message indicates it is send in reply to a solicitation message  If a reply to the neighbor solicitation message is received auto configuration aborts

55. © Janice Regan, 2012 55 IPv6 auto configuration (3a) . 3. Send router solicitation from the link local address to the all routers multicast address 4. If no router advertisements are received this indicates there is not IPv6 capable router available  The node will attempt to obtain an IP address using DHCPv6  If no DHCPv6 server is available the node communicates to other IPv6 hosts only locally, using the link local address (skip remaining autconfig steps)

56. © Janice Regan, 2012 56 IPv6 auto configuration (3b) . 3. Send a router solicitation message from the link local address to the all routers multicast address 4. Any IPv6 router that receives the router solicitation message will reply with a router advertisement unicast to the link local address of the auto-configuring node

57. IPv6 auto configuration (4)  Use the parameters in the RA (or from DHCPv6) to set the parameters of the interface (MTU, Retrans time, Reachable time, Hop Limit)  Choose default routers (Lifetime ≠0). Note that only default routers can have default routes  Use each of the prefixes with the A flag set in the RA (or from DHCPv6) to determine global address, test address with DAD, and initialize corresponding global address on the interface  Each interface has 1 address for each prefix © Janice Regan, 2012 57