ZyXEL Confidential

ICMPv6Feng ZhouSW2ZyXEL Communications Corp.03/27/2006

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Outline Review ICMPv4 Overview of ICMPv6 ICMPv6 Error Messages ICMPv6 Informational Messages ICMPv4 vs. ICMPv6 Path MTU Discovery Q&A

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Review ICMPv4 ICMPv4 Header

protocol field in IPv4 header is 1

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TypeCode

ChucksumMessage Body

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Overview of ICMPv6 Next Header = 58 Functions

• Reporting errors

• Diagnostic function for troubleshooting

• Additional information message– ND (Neighbor Discovery)

– MLD (Multicast Listener Discovery)

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Overview of ICMPv6 Types of ICMPv6 Messages

• Error Messages– Report forwarding or delivery errors by either a router

or the destination host

• Informational Messages– Provide a simple diagnostic capability to aid in

troubleshooting

– MLD and ND

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Overview of ICMPv6 ICMPv6 Header

Type(8bits): Indicates the type of ICMPv6 message.Code(8bits): Differentiates among multiple messages

within a given message type.Chucksum(16bits): Stores a checksum of the ICMPv6

message.Message Body: Contains ICMPv6 message-specific

data.

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TypeCode

ChucksumMessage Body

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ICMPv6 Error Messages Type: 0~127 (the first bit of Type field is 0) Consist

• Destination Unreachable– The packet cannot be forwarded to the destination node or upper-

layer protocol

• Packet Too Big– The packet cannot be forwarded because the link MTU on the

forwarding interface of a router is smaller than the size of the IPv6 packet

• Time Exceeded– The Hop Limit field in the IPv6 header becomes zero after

decrementing its value during the forwarding process

• Parameter Problem– There is an error in the IPv6 header or an extension header that

prevents IPv6 from performing additional processing

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ICMPv6 Error Messages Rate limiting

• To conserve network bandwidth, ICMPv6 error messages are not sent for every error encountered, they are rate limiting

• Rate limiting can be based on either of the following:– A timer

● One error message per source or any source for every T ms. RFC 2463 suggests a value of 1000 ms

– A percentage of bandwidth● Error messages sent per interface is some percentage P of the link's bandwidth. RFC 2463 suggests a value of 2%

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Destination Unreachable Message Structure

• Portion of Discarded Packet: fit as much invoking packet as possible without exceeding the minimum IPv6 MTU

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TypeCode

ChucksumUnused

Portion of Discarded Packet

=1=0~4

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Destination Unreachable Code Field Value

Code Description Example

0 No Route to Destination

No route matching the destination was found in the routing table

1 Communication with Destination Administratively Prohibited

packet is discarded by a firewall

2 Beyond Scope of Source Address

packet is forwarded using an interface that is not within the scoped zone of the source address

3 Address Unreachable

an inability to resolve the destination's link-layer address

4 Port Unreachable Packet received but no application

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+ Frame: Base frame properties+ ETHERNET: EType = IPv6

IP6: Version = 6 (0x6) IP6: Traffic Class = 0 (0x0) IP6: Flow Label = 0 (0x0) IP6: Payload Length = 88 (0x58) IP6: Next Header = 58 (ICMP6)IP6: Hop Limit = 128 (0x80) IP6: Source Address = fec0::2:201:2ff:fe44:87d1 IP6: Destination Address = fec0::2:260:97ff:fe02:6e8f IP6: Payload: Number of data bytes remaining = 88 (0x0058)

ICMP6: Destination Unreachable (No route) ICMP6: Type = 1 (Destination Unreachable)ICMP6: Code = 0 (No route)ICMP6: Checksum = 0xD498ICMP6: UnusedICMP6: Data: Number of data bytes remaining = 80 (0x0050)

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Packet Too Big Message Structure

• MTU: stores the link MTU of the interface over which the packet was being forwarded

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TypeCode

ChucksumMTU

Portion of Discarded Packet

=2=0

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Time Exceeded Message Structure

Code• 0 (Hop Limit Exceeded in Transit)

– Sent by a router when the Hop Limit field in the IPv6 header is decremented to 0, or this value of an arriving packet is 0

• 1 (Fragment Reassembly Time Exceeded)– Sent by a host when the fragmentation reassembly time of the

destination host expires

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TypeCode

ChucksumUnused

Portion of Discarded Packet

=3=0 or 1

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Parameter Problem Message Structure

• Pointer: indicates the byte offset (starting at 0) in the IPv6 packet at which the error was encountered

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TypeCode

ChucksumPointer

Portion of Discarded Packet

=4=0~2

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Parameter Problem Code Field Value

Unrecognized IPv6 Option Encountered message is used when both of the following are true:

• An option in a Hop-by-Hop Options header or a Destination Options header is not recognized.

• Within the option's Option Type field, the 2 high-order bits are set to either 10 (binary) or 11 (binary)

Code Description0 Erroneous Header Field Encountered

1 Unrecognized Next Header Type Encountered

2 Unrecognized IPv6 Option Encountered

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ICMPv6 Informational Messages Type: 128~255 (the first bit of Type is 1) Consist

• Echo Request– Sent to a destination to solicit an immediate Echo

Reply message. The Echo Request/Echo Reply message facility provides a simple diagnostic function to aid in the troubleshooting of a variety of reach ability and routing problems

• Echo Reply– Sent in response to the receipt of an ICMPv6 Echo

Request message

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Echo Request Message Structure

• The Identifier and Sequence Number fields are set by the sending host so that they can be used to match an incoming Echo Reply message with a sent Echo Request message

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TypeCode

ChucksumIdentifier

Sequence NumberData

=128=0

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Echo Reply Message Structure

The Identifier, Sequence Number, and Data fields are set with the same values as those in the Echo Request message that prompted the Echo Reply

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TypeCode

ChucksumIdentifier

Sequence NumberData

=129=0

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ICMPv4 vs. ICMPv6ICMPv4 ICMPv6

Destination Unreachable-Network Unreachable (Type 3, Code 0)

Destination Unreachable-No Route to Destination (Type 1, Code 0)

Destination Unreachable-Host Unreachable (Type 3, Code 1)

Destination Unreachable-Address Unreachable (Type 1, Code 3)

Destination Unreachable-Protocol Unreachable (Type 3, Code 2)

Parameter Problem-Unrecognized Next Header Type Encountered (Type 4, Code 1)

Destination Unreachable-Port Unreachable (Type 3, Code 3) Destination Unreachable-Port Unreachable (Type 1, Code 4)

Destination Unreachable-Fragmentation Needed and DF Set (Type 3, Code 4)

Packet Too Big (Type 2, Code 0)

Destination Unreachable-Communication with Destination Host Administratively Prohibited (Type 3, Code 10)

Destination Unreachable-Communication with Destination Administratively Prohibited (Type 1, Code 1)

Source Quench (Type 4, Code 0) This message is not present in IPv6

Redirect (Type 5, Code 0) Neighbor Discovery Redirect message (Type 137, Code 0)

Time Exceeded-TTL Exceeded in Transit (Type 11, Code 0) Time Exceeded-Hop Limit Exceeded in Transit (Type 3, Code 0)

Time Exceeded-Fragment Reassembly Time Exceeded (Type 11, Code 1)

Time Exceeded-Fragment Reassembly Time Exceeded (Type 3, Code 1)

Parameter Problem (Type 12, Code 0) Parameter Problem (Type 4, Code 0 or Code 2)

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Path MTU Discovery PMTU

• the smallest link MTU supported by any link in the path between a source and a destination

Link MTU• the maximum-sized link-layer payload that

can be sent on the link

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Path MTU Discovery PMTU Discovered Process1. The sending node assumes that the destination PMTU is the link MTU

of the interface on which the traffic is being forwarded2. The sending node sends IPv6 packets at the assumed PMTU size3. If a router on the path is unable to forward the packet, it sends an

ICMPv6 Packet Too Big message back. The ICMPv6 Packet Too Big message contains the link MTU of the interface on which forwarding failed

4. The sending node sets the new assumed PMTU to the value of the MTU field in the ICMPv6 Packet Too Big message

The sending node starts again at step 2 and repeats steps 2 through 4 until when either no Packet Too Big messages are received or an response or acknowledgment packet is received from the destination.

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Changes in PMTU Decreases in path MTU

• Immediately discovered through the receipt of ICMPv6 Packet Too Big messages

Increases in path MTU• Detected by the sending node. The sending

node can attempt to send a larger IPv6 packet after a minimum of 5 minutes (10mins are recommended) upon receiving an ICMPv6 Packet Too Big message

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Path MTU Discovery FlowchartSet PMTU to Link MTU

Send packet at PMTU Size

Set PMTU to Link MTUPacket Too Big received

N

PMTU < Link MTU

N

Y PMTU timer expired?

Y

Y

N

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Q&A

Q & A

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Date Subject Lecturer

Introduction to IPv6

IPv6 Addressing

IPv6 Header & Extensions

Neighbor Discovery Protocol

Multicast Listener Discovery

IPv6 Routing

ICMPv6

Address Autoconfigurator

Joe Zhao

Milo Liu

Joe Zhao

Feng Zhou

Billy Bian

Jeffrey Zhou

Feng Zhou

Milo Liu

03/10

03/16

03/23

03/27

03/30

03/30

04/06

04/06

Training course arrangement

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Date Subject Lecturer

Setting Up an IPv6 Test Lab

IPv6 Migration Mechanisms

IPv6 Mobility

Joe Zhou

Milo Liu

04/13

04/20

Training course arrangement